The Life History of the Common New Zealand Skink Leiolopisma zelandica (Gray, 1843)
[Received by the Editor, March 6, 1958.]
In a study area of a quarter acre, a population of at least 222 lizards was determined by marking and recapture over a two-year period. The species Leiolopisma zelandica is described. Variation in numbers of head plates and body scales and in relative proportions is determined. The testes are at minimal mass in June-July, enlarging during summer. Copulation is described. Ovulation occurs in October, gestation is twelve weeks, parturition is in January. Three to five young are born per female. Earlier ovulation and two young per female are shown by Leiolopisma aeneum.
The young increase two and a-half times in weight before hibernating when growth ceases. In the next growing season the young reach small adult size at 16 months and become sexually mature at 20 to 21 months. Growth continues throughout life, becoming progressively slower. Young in their first year form the only distinct age-size class. Sixty-five per cent of captures had broken or regenerating tails which are rarely as long as the original and have different scalation. Food was in order of preference spiders, hemipterans, coleopterans, isopods and amphipods. One-third of the lizards examined were infected rectally with a nematode Pharyngodon sp.
L. zelandica has a definite home range of about 15 square yards; home ranges overlap considerably. Aggressive territorial behaviour was not observed. Juveniles show no home range behaviour. In Wellington only partial hibernation occurs; the period is four and two-thirds months. Moulting was observed in October-November and is completed within 24 hours, the epidermis being shed in patches.
The small brown skink Leiolopisma zelandica (Gray, 1843) is perhaps the most abundant and widely distributed New Zealand reptile. It is therefore remarkable that the life history and habits of this lizard, known since the days of New Zealand's first explorers, have never been more than casually discussed. Indeed, few facts have been recorded concerning the habits, ecology or life history of any New Zealand lizard.
Leiolopisma zelandica was first described by Gray in 1843 as Tiliqua ornata from material collected by Ernst Dieffenbach during his travels as naturalist to the New Zealand Company. Gray's description was incorporated in Dieffenbach's “Travels in New Zealand” and subsequently in the “Catalogue of Lizards in the Collection of the British Museum” which Gray published in 1845. Numerous changes of name and position were later accorded to the species, which was included in Boulenger's great Catalogue of 1887 as part of the species Lygosoma moco. McCann (1955) distinguished and redescribed Leiolopisma zelandica as a valid species in his recent revision of the lizards of New Zealand.
The genus Leiolopisma has a wide distribution; Asia, North and Central America, Australia, and New Zealand. No extensive account of any member of the genus has yet appeared. Lewis (1951) described some aspects of the biology of Leiolopisma laterale (Say) which occurs in the eastern and southern United States. Breckenridge (1943) and Fitch (1954) have carried out detailed studies on the life histories of two oviparous scincid lizards, both of the genus Eumeces. The most comprehensive of these accounts is that by Fitch, who studied the life history and
ecology of Eumeces fasciatus (Linnaeus) over a five-year period. The life history of Leiolopisma zelandica is not entirely comparable with that of skinks studied in detail by previous workers, since the species is viviparous. So far as is known, the present study is the first to appear on a viviparous skink.
Leiolopisma zelandica is a quietly moving, wary lizard, secretive in its habits and usually seen moving in a normal manner only when the observer remains still and quiet in one spot. The species lives in almost any small area offering sufficient cover, moisture, food, and sunlight. Almost every city garden, coastal beach and shingle river bed has a skink population. Where suitable habitats are present, the species occurs well inland, although it is generally more plentiful in coastal areas. Under optimum conditions local populations may be very large, far larger than is apparent to the casual observer.
New Zealand does not have a very diverse fauna, and the skink has few direct competitors. This, together with the absence of a wide range of skink predators, means that skinks are relatively secure animals capable of forming dense local populations.
The study presented here has been primarily a field one, carried out to determine the main features of reproduction, growth habits and behaviour, and was conducted in an area containing what proved to be a denser population of Leiolopisma zelandica than was originally anticipated. This area lies within the limits of the city of Wellington and was sufficiently close to the university to allow field observations to be made at regular intervals. The study commenced in March, 1954, and was continued to October, 1955, the period being long enough to obtain information on many aspects of the natural history of Leiolopisma zelandica, the common brown skink.
Description and Variation
McCann (1955) describes all the known members of the New Zealand Scincidae, including Leiolopisma zelandica (Gray, 1843), and Leiolopisma aeneum (Girard, 1857) and discusses in detail the synonymy of the New Zealand species. The description given below of Leiolopisma zelandica is based upon an examination of 50 specimens from several localities in the Wellington district, and is more detailed than that of McCann. Specimens of L. zelandica were collected from Kelburn, Brooklyn, Island Bay, York Bay, and Somes Island, all close to Wellington City, and from Pukerua Bay, 18 miles north of the city.
Leiolopisma zelandica (Gray, 1843)
Habitat lacertiform; snout short, profile moderately obtuse, anterior ⅔ head contour is wedge-shaped, posterior ⅓ parallel-sided, passing evenly to moderately elongate body; limbs well-developed. Undamaged tail length 1.0 to 1.2 the distance between snout and vent. Distance between tip of snout and fore-limb 1.2 to 2.0 (2.0 +) in the distance between the axilla and groin.
Rostral moderately large (Text-fig. 1); dorsolateral margins excavate and with posteroventral wings below on each side, the area visible from above being slightly more than ½ of the area of the frontonasal; twice as broad as long; short convex median junction with the frontonasal about equal to ⅙ the width of the frontal; long, concave sutures with the nasals; short vertical sutures with the 1st upper labials. Nasals moderate, narrowly separated by rostral-frontonasal suture; irregularly pentagonal; horizontal suture with upper edge of 1st upper labial and forward edge of anterior loreal. Nostril pierces centre of nasal. No supranasals or postnasals. Anterior loreal rhombic, posterior border against posterior loreal; ventral against 2nd upper labial and dorsal narrowly contacts frontonasal and still less the prefontal. Frontonasal large, diamond-shape, about equal in area to frontal from which it is excluded by the median junction of the prefrontals; narrowly in contact with
Text-fig. 1.—The head plates of Leiolopisma zelandica. (1) Lateral view head plates. (2) Dorsal view head plates. (3) Ventral view chin shields. Key: AL, anterior loreal; C, chinshields; F, frontal; FN, frontonasals; FP, frontoparietals; GU, gulars; IP, interparietal; LL, lower labial; M, mental; N, nasal; NU, nuchals; P, parietal; PF, prefrontal; PG, postgenials; PL, posterior loreal; PLA, post labials; PM, post mental; PO, preocular; POC, postocular; PS, presuboculars; PT, primary temporal; R, rostral; SC, superciliaries; SO, supraoculars; ST, secondary temporals; TT, tertiary temporals; UC, upper ciliaries; UL, upper labials.
nasals and prefrontals. Prefrontals large, each equal to ⅗ the area of the frontal; irregularly elongate ovoid; convex sutures with frontal and 1st supraocular; shorter sutures with anterior loreal and preocular. Frontal large, kite-shaped, length equal to its greatest width; wider than supraocular region; longest sides against 1st and 2nd supraoculars, short convex sutures with frontoparietals. Frontoparietals paired, right longer than left; longest sutures with each other then next in length with interparietal; shallowly concave sutures with the 2nd, 3rd and 4th supraoculars; concave sutures with parietals. Interparietal kite-shaped; smaller than frontal; enclosed between frontoparietals and parietals; pineal area apparent just behind midpoint of shield. Parietals largest head shields, as long as frontoparietals and interparietals together; irregular oblongs, long axes of each shield diverge from each other at about 80°, more than twice the length of the short axis; parietals meet in a short suture sloping back towards the left; other sutures, long and straight with uppermost secondary temporal, less long with the interparietal, still less with the frontoparietal and first nuchal and considerably shorter with the 4th supraocular, 1st and 2nd postoculars; the right parietal shield also narrowly meets the first nuchal on the left side. One to five, usually three pairs of nuchals, rarely more, often extra unpaired nuchal, each twice width of the dorsal scales, with which they often gradually merge.
Six to nine, usually seven upper labials; 1st small, square, in contact with nasal dorsally; 2nd, 3rd and 4th similarly shaped, slightly larger and higher; 2nd in contact with both loreals, 3rd with posterior loreal and presuboculars; 5th larger
than preceding four, immediately below centre of eye, 6th and 7th taller than 5th. Two large postlabials are separated from ear opening by 2 small projecting lobules. Three postoculars. Primary temporal, roughly hexagonal bordering the second upper postocular, lower postocular, upper and lower secondary temporal, 6th and 7th upper labials. Upper secondary temporal twice the size of the primary temporal, larger than the lower secondary temporal. The two tertiary temporals are a little larger than the following body scales. Body scales begin behind the nuchals, tertiary temporals and posterior postlabials.
The paired loreals are moderate, subequal in size, irregularly quadrilateral; the anterior lying between the nasal, frontonasal, prefrontal, posterior loreal and 2nd upper labial; the posterior loreal bordered by the prefrontal, preocular, 1st presubocular and 2nd and 3rd upper labials. Single preocular, 3 presuboculars, 1st largest, 3rd smallest. Eye completely surrounded by elongate rectangular granules, forming above a row of 5 or 6 supraciliaries, with a similar number below. Lower eyelid, with an undivided, transparent palpebral disc about as large as the ear opening surrounded by small oblong granules. The eye is bounded above by a row of 7 or 8 superciliaries; below by 3 presuboculars, 5th and 6th upper labials, 1st upper postocular and lower postocular. The superciliaries are bordered anteriorly by the preocular; above by 1st to 4th supraoculars; posteriorly by the 1st upper postocular. Four well developed supraoculars, 2nd largest; then 1st, 3rd and 4th in turn.
Mental shield larger than rostral, postmental 1½ times the size of mental; followed by 3 pairs of chinshields; the first pair are in contact, the second pair separated by a single scale row, the third by 3 scale rows. Six lower labials, the 3rd, 4th and 5th being the largest.
Ear opening round or oval, about as large as palpebral disc, with 3 auricular lobules projecting feebly from its anterior border. Scales 28 to 32 at midbody, feebly striate, dorsals largest. Preanals, inner two largest. Limbs well developed, hind-limbs longer than fore-limbs; adpressed limbs meet, just fail to meet or overlap; fore-limb reaching rear corner eye opening or below centre of eye; pentadactyle; digits slender, subcylindrical, subdigital lamellae smooth, 20 to 25 under 4th toe hind-limb. Palms and soles granular.
Ground colour yellowish-brown, varying from a pale-straw colour to a strongly melanistic brown; dorsal scales have 4 or more black lines on their surface giving a striate appearance. Median longitudinal stripe, 2 half scale rows wide, partially or well-developed, commencing at nuchals and passing back over the first third of tail, frequently bordered by a narrow straw-coloured stripe; passing to a wide dorsal band, 2½ scale rows wide, yellow-brown with a well-defined lateral border. A fine dorsolateral light line 2 half scale rows wide, commencing above the anterior border of the eye and carrying backwards along either side of the tail, with a well defined lateral border (formed by a very dark brown lateral band).
A prominent broad lateral band 1 and 2 half to 2 and 2 half-scale rows wide, dark brown in colour, originating at the tip of the snout, passing through the eye and terminating towards the end of the tail, regularly notched above and below by lighter coloured scales extending into it, broken into irregular blotches or flecked with black and white spots; below this a very light yellow-brown stripe, one half to 1 scale row wide passes from beneath the anterior border of the eye through ear, above limb insertions, to the tail, irregularly defined below by sparsely pigmented scales which merge gradually with the even greenish-yellow ventral colouration, which also extends over the ventral surface of the limbs.
Any or all of the longitudinal stripes may become indistinct over the posterior third of the tail. Regenerated tail often dark orange-brown colour distinct from any other body colour. The fore and hind-limbs show the typical yellow-brown colour of the broad dorsal bands; frequently a narrow light-straw coloured stripe passes from the limb origin along the anterior face of the limb to the manus or pes, sometimes showing as a series of irregular blotches.
In an endeavour to detect body colour and pattern changes, the colouration of 26 newly-born juveniles was recorded in detail; as yet none of these lizards has been recaptured. The newborn are similarly patterned to the adult, with no distinctive juvenile colouration. The light-straw colour of the juveniles of L. zelandica gives way to a darker brown ground colour in large adults, generally with less distinct body striping.
Table I, based upon an examination of 50 L. zelandica of 35.0 mm or more from snout to vent, shows the variation encountered in several characters. The number of upper and lower labials, nuchals, scales around the middle of the body and subdigital lamellae under the 4th toe hind limb, vary. The number of lower labials varies more than the number of upper labials, 7 being the usual number in each case; two exceptions were found in this number in the upper labials and 20 exceptions in the lower labials. The number of nuchals varies from 1 to 5, though in one specimen they were entirely lacking. An even number was present in 26 specimens, 19 had one extra nuchal and four had 2 extra nuchals. In 23 lizards, 3–3 or 2–3 nuchals were present, these being the most frequent arrangements occurring. The number of scales round the middle of the body ranges from 28 to 34, with 29 or 30 in two-thirds of the specimens examined. The subdigital lamellae under the 4th toe hind limb vary in number from 20 to 24, being 20, 21 or 22 in three-quarters of the lizards examined. Detailed examination has failed to show that the variation listed above is the product of sex or age differences.
The ratio, snout-forelimb length to axilla-groin length, shows that there is a tendency for increased relative torso length in adult lizards. This is also reflected in the adpressed limbs, which may overlap, meet, or fail to meet. The adpressed limbs of adult lizards 48.0 mm or more from snout to vent fail to meet more frequently than those of sub-adult and juvenile lizards. The ratio, snout-forelimb length to axilla-groin length, for 22 lizards of 47.9 mm or less from snout to vent is 1.2 to 1.7; and for 43 lizards of 48.0 mm or more, 1.4 to 2.2. Sex differences were observed, such as a relatively broader head in males over 55.0 mm in snout-vent length, but the sample available was unsuitable for study of sex variations since it contained only 30% of males
The Study Area
Shortly after the commencement of this study a large population of Leiolopisma zelandica was found to be present in an abandoned cemetery adjacent to Victoria University. The area was an obvious choice as a site for a marking programme because of its close proximity to the laboratory, which allowed frequent observations to be made. It is overgrown by introduced and indigenous trees, shrubs and weeds, and is roughly triangular in shape, lying along the top and southern slopes of a small ridge running in a north-easterly direction towards Wellington Harbour. The surrounding land has been modified to some extent by roading and building excavations that form steeply sloping banks 3 feet to 25 feet high, dropping to paths or roads which border the cemetery on all three sides.
The top of the ridge lies some 300 feet above sea-level, falling to 250 feet at its most northerly point. Sloping away from the upper ridge is a small gully with a south-east aspect whose floor lies about 30 feet below the ridge. The narrow ridge-top strip is open to the sun, whereas the gully is shaded at all times by a thicket of trees and shrubs. The ridge is fully exposed to the two prevailing winds—i.e., from the north and the colder southerly wind.
[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]
|Labials. n = 50.||Nuchals. n = 50.|
|No. Upper Labials.||No. Lower Labials.||Paired = 27 indiv.||Unpaired = 22 indiv.|
|No. of Labials or Nuchals.||7||8||9||6||7||8||0+0||1 + 1||2 + 2||3 + 3||4 + 4||1 + 2||1 + 3||2 + 3||3 + 4||3 + 5||4 + 5|
|Frequency. (No. of Specimens.)||48||1||1||16||30||4||1||5||4||16||1||2||3||12||3||1||1|
[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]
|Scales Round Mid-body. n = 50||Subdigital Lamellae 4th toe, hind limb. n = 48|
|No of Scales or Lamellae.||28||29||30||31||32||33||34||20||21||22||23||24|
|Frequency. (No. of Specimens.)||7||18||15||3||6||—||1||10||14||13||5||6|
[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]
|Relationship of Adpressed Limbs.||Ratio. Snout to Fore-limb Length: Axilla to Groin Length.|
|Snout-vent length in mm.||Do Not Meet||Meet||Overlap||1.2||1.3||1.4||1.5||1.6||1.7||1.8||1.9||2.0||2.1||2.2|
Text-fig. 2 is a detailed plan of the ridge-top section in which the majority of skinks were marked. The quarter-acre plot is rectangular in shape, 180ft long by 60ft wide, with the longest dimension lying in a north-east to south-west direction, and comprises about one-third the total area of the cemetery. Over two hundred skinks of the species Leiolopisma zelandica were caught and marked within this narrow strip during the period from March, 1954, to October, 1955.
The graves of the cemetery, mostly surrounded or covered with concrete or brick, provide a litter of flat stones and bricks giving adequate cover to the skink population. There are numerous crevices in the stonework and narrow spaces which harbour many skinks, especially during the hibernation period. Many of the graves are bordered by a profuse growth of weeds and shrubs which either completely obscures the stonework or leaves “islands” of concrete which serve as basking places for L. zelandica.
The substratum consists of a thin layer of clay-loam varying in thickness from 2 to 10 inches, and overlying the typical mixture of rotten rock and clay produced through the decay of greywacke rock.
The trees of the area include both introduced and indigenous species. The indigenous species are: coprosmas (Coprosma repens and C. lucida), akeake (Dodonea viscosa), ngaio (Myoporum laetum), puriri (Vitex lucens), pohutukawa (Metrosideros excelsa), mahoe (Melycitus ramiflorus), karo (Pittosporum crassifolium), tarota (Pittosporum eugenioides), kowhai (Sophora tetraptera) and the New Zealand cabbage tree (Cordyline australis).
A few specimens of holly (Ilex aquifolium) with single specimens of yew (Taxus baccata) and Viburnum odoratissimum make up the introduced trees within the plot, although there are many more in the southern hollow. Grasses, predominantly brome (Bromus cartharticus) with some cocksfoot (Dactylis glomerata), Yorkshire fog (Holius lanatus), couch grass (Agropyron repens) and brown top (Agrostis tenuis) carpet the area in patches, mixed with weeds. Common amongst the weeds are vetches (Vicia sp.), cleavers (Galium aparine), black nightshade (Solanum nigrum), black medick (Medicago lupulina), spurge (Euphorbia peplus) and cow-thistle (Sonchus oleraceus). In the early spring the wild onion (Allium triquetrum) forms large clumps, as do several species of common wood sorrels (Oxalis sp.) These give way to grasses in the summer and autumn.
Within the quarter-acre strip three sets of traps were used, marked A, B and C in Text-fig. 2. Set “A” on the lower level was surrounded by a belt of grass, mostly Bromus cartharticus, which was in turn bordered by a patch of gorse (Ulex europeus) mixed with broom (Cytisus scoparius), this continues as a horseshoe-shaped belt around the lower edge of the gully and butts on to the study area at its upper end. The traps in “B” partly extended into a patch of periwinkle (Vinca major), fennel (Foeniculum vulgare) and vetch, forming a tangled mass two to four feet high inhabited by large numbers of skinks. Part of this area was further overgrown by a tangled growth of honeysuckle (Lonicera japonica) and a shrubby valerian (Kentranthus ruber). Traps “C” were set on a moderate slope which was sparsely covered with short grasses and patches of valerian 2 to 3 feet tall.
The scattered trees and shrubs together with the fennel, periwinkle, valerian and honeysuckle, form a litter layer from 2 to 6 inches thick which in some parts remains moist all the year round, and contains a rich source of arthropod food for the skinks. There is no running or standing water in the strip. In winter the ground is very damp, with a few small pools of water following rain, but dry conditions generally persist through January to late March or early April. During this latter period the grasses and weeds die down and form in places a thick mat that retains considerable moisture close to the ground surface.
Almost two-thirds of the skinks caught within the study area and all skinks caught elsewhere were caught by hand. Active searching accompanied by turning or lifting of rocks, bricks and any other readily movable objects within the collecting areas exposed skinks which could then be taken by hand. This method was generally more effective when temperatures were sufficiently low to slow down the movement of the animals.
Two traps of the pitfall type were tested. The first of these, a wide-mouth glass preserving jar sunk in the ground so that the top of the jar was flush with the surface, was unsuccessful, probably due to poor siting. Few captures occurred even when the trap was baited with rotting fruit to attract flies. This type was subsequently abandoned. A serious disadvantage of this trap was the tendency to fill with water in wet weather, a problem overcome with the second type of trap adopted, which consisted of a six-inch length of galvanised iron downpipe, 3 inches in diameter, buried as before with its upper lip flush with the surface of the ground. The lower open end allowed water to quickly drain away, and an inch or two of soil filled the bottom of the trap. This soil was soon colonised by a variety of amphipods, isopods and insects, providing an abundant food supply for trapped skinks. Skinks were observed on more than one occasion to examine the interior of the trap, stretching out and looking down into the bottom, before dropping down to the soil beneath.
Both types of trap were covered with a slab of rock or brick supported above the trap lip so as to leave ample room for a skink to enter. A serial number painted on the inside of each trap was used in recording the location of capture of each lizard.
The lizards were marked by clipping the toes in various combinations. Generally no more than three toes were clipped with a maximum of two toes on any one foot. The toes were removed close to the second joint with a pair of fine-pointed scissors. Any toes lost through natural causes were incorporated as conveniently as possible into the marking system. In no case were the toes found to regenerate. The method proved to be very satisfactory; the only difficulty experienced occurred in cases of toes lost through natural causes subsequent to marking. These were often plainly apparent as the marked toes were cut at a constant point and those lost naturally rarely coincided.
The marking of each skink was carried out in the field immediately upon capture or removal from a trap. The trap number, or the point of capture together with any other relevant details, was recorded at the same time. All skinks were then carried in cages to the laboratory for weighing and measuring.
The weight, together with a series of measurements for each lizard, was taken in the laboratory. All measurements were made in millimetres to the nearest 0.5 of a millimetre, and recorded on individual index cards. Each lizard was laid in the supine position and held at the mid-body point with the fingers of both hands. The skink was then gently stretched out by stroking towards the head and tail. This process was repeated for up to three or four minutes if necessary, until the well known state of false hypnosis shown in many species of lizards was induced. Juveniles can be quieted in a shorter time than adults. The small size of L. zelandica rendered this method necessary. The method gave consistently good results.
Each lizard was weighed on a laboratory scale, to the nearest tenth of a gram. Some difference between weights recorded for the one lizard at short intervals may have been due to the presence or absence of food in the skink's alimentary tract. In most cases, however, each animal was held in captivity for 24 hours without food before weighing.
At every opportunity skinks were collected from localities other than the study area selected. Some of these captured were kept in terraria, where their behaviour was observed. Most were preserved and subsequently used for data on variation, the seasonal cycles of the gonads, and the gastrointestinal contents.
Seasonal Cycle of Reproduction
Seventy-eight specimens of Leiolopisma zelandica were collected from the Wellington area, including the Kelburn, Brooklyn, York Bay, Island Bay and Somes Island districts, all adjacent to Wellington City, as well as Pukerua Bay, on the west coast of the North Island, eighteen miles north of Wellington City. The state of development of the gonads of these lizards suggests a well defined gonadal cycle. A few specimens of Leiolopisma aeneum collected from Pukerua Bay showed some differences in the gonadal cycle from that of L. zelandica.
For the greater part of the year there is little difference in the external appearance of males and females, though from November until early February, females carrying young may be recognised by the distended abdomen, and adult males 55.0 mm or more from snout to vent can sometimes be distinguished by a relatively larger head. Males of L. zelandica do not assume an early spring breeding colouration which allows the sex of some other species of skinks to be determined. Moreover, the method whereby males can be induced to evert their hemipenes through pressure exerted at the base of the tail close behind the cloaca, is not reliable in adults of this species, and gives no results in juveniles. Thus no reliable method of sexing live individuals of Leiolopisma zelandica is known, and the sex of adults cannot always be decided even in the breeding season.
The following account of the reproductive cycle of L. zelandica is based on the preserved collection of 78 specimens mentioned above. Because of the difficulty of sexing these specimens externally, the ratio of males to females was not known until they were dissected, when it was found to be one to two. The number of males was not adequate for a full analysis of the reproductive cycle, and there has been no opportunity to obtain further material for all seasons.
Seasonal changes taking place in the gross morphology of the ovaries and oviducts have been studied from 52 specimens of immature and mature Leiolopisma zelandica. In addition 13 specimens of L. aeneum from Pukerua Bay were examined for comparison.
The female reproductive organs consist of equally well developed right and left ovaries and paired oviducts which open separately into the cloaca. The ovaries are elongate oval bodies lying posteriorly and dorsally in the body cavity. The completely transparent ovarian epithelium permits the individual ova to be seen. Each ovary is suspended by a mesovarium midway along the oviduct. The right oviduct is 5.0 mm or so longer than the left, so that the right ovary lies more anteriorly than the left.
In a sub-adult female (less than 50.0 mm in snout-vent length) the ovaries are small, 3.0 mm to 4.0 mm in overall length, with a cluster of pale whitish ova each less than 0.75 mm in diameter. Adult lizards collected during a non-breeding period (i.e., February to March) show six to fourteen whitish opaque ova in each ovary, varying in diameter from 0.1 to 2.5 mm.
L. zelandica has one breeding season in each year; but the ovary contains ova of graduated sizes. From February to April in any one adult ovary there are usually two to three large ova (1.5 mm to 2.5 mm in diameter) at the same stage of development, two or three ova 0.75 mm to 1.0 mm in diameter and seven to eight ova less than 0.75 mm. From April until October large developing ova reaching
6.5 mm in diameter at the end of the period are found within the ovaries. Development of these ova takes place during the hibernation period from early April to the beginning of September, continuing in the early spring until ovulation takes place in the first weeks of October.
Following the rupture of each follicle at ovulation a pale corpus luteum develops within the ovary of L. zelandica and persists until parturition takes place some twelve weeks later. Counts of the corpora lutea present have been used in this study to determine the number of ova released by each ovary in L. zelandica.
The presence of a corpus luteum in reptiles has been recognised since Strahl (1892) described the corpus luteum in Lacerta agilis. Weekes (1934) reviews the early work and describes the corpus luteum in a number of oviparous and viviparous reptiles, including Lygosoma (Leiolopisma) weeksae and Lygosoma (Leiolopisma) entrecasteauxt as well as three other scincid lizards. In the viviparous lizards examined by Weekes the corpus luteum persists for approximately three and a-half months, degeneration beginning at about the end of the second month of pregnancy. By the time of birth of the young, the degeneration has spread through all the luteal tissue, which disappears two weeks after the birth of the young. Boyd (1940), Dutta (1944) and Miller (1948) further established that well developed corpora lutea are formed in several other families of lizards.
The average mass of the ovum at ovulation is 0.10 gm and the average mass of the newly born young 0.26 gm. It follows, then, that more than half the total weight of the fully developed young must be derived from materials transported across the oviduct wall. Thus some form of placentation exists in L. zelandica and the species is truly viviparous, the ova being retained in the oviducts as is the case in all other New Zealand lizards.
Placentation is known to occur elsewhere in the family Scincidae, and Weekes (1935) in a review of placentation among reptiles records two types of placentation within the genus Leiolopisma. The placentation of five Australian members of the genus has been examined: Lygosoma (Leiolopisma) pretiosum, L. (L.) ocellatum, and L. (L.) metallicum (Weekes, 1930). These have a simple type of placentation whereas Lygosoma (Leiolopisma) entrecasteauxi (Harrison and Weekes, 1925) and L. (L.) weeksae (Weekes, 1929) have an extremely specialised placenta. The nature of the placentation in L. zelandica has not yet been examined.
The mature oviducts are superficially pleated externally, folded and flattened against the dorsal body wall. The right oviduct, 18.0 mm to 22.0 mm long, is 4.0 mm or 5.0 mm longer than the left. In immature females the oviducts are folded for the first third of their length, and the remaining portion is a flat ribbon-like band of semi-opaque tissue 1.0 mm to 2.0 mm wide (Text-fig. 3). The gravid oviduct is greatly distended and appears as though chambered. The oviducts of mature females are generally folded and pleated throughout their entire length, especially following parturition, but do not show the distinct “incubatory chambers” which persist in some other lizards.
The first two newly-born young of the 1954–55 breeding season were caught within the study area on January 20, 1955. No more were captured for four days, despite prolonged and careful searching. Then 16 newly-born lizards were taken on January 25 and 26, ranging in size from 24.5 mm to 28.0 mm snout-vent length. The newly-born lizards grow rapidly, and as the first two lizards caught on January 20 were 28.0 mm and 29.5 mm from snout to vent they may have been born towards the beginning of January. A large female weighing 5.2 gm before parturition gave birth to six young from 0.26 to 0.28 gm in weight and averaging 24.9 mm in snout-vent length. Both size and weight appear to be fairly constant for newly-born young. Twenty-two young lizards were caught during the following ten weeks, and by comparing their size with the known rate of growth it could easily be seen that none could have been born later than the middle of February. By the end of February all lizards captured were above 30.0 mm from snout to vent.
When copulation takes place amongst the adults, presumably in October, the young of the year have reached 35.0 mm to 40.0 mm and the ovaries of five such young females examined were about 1.0 mm long, each with a number of small, white opaque follicles less than 0.75 mm in diameter.
The ovarian follicles gradually increase in size, reaching a maximum of 2.0 mm in diameter at the commencement of the lizard's second hibernation when it is 16 months old and 50.0 mm in snout-vent length. The ova enlarge rapidly during the lizard's second hibernation and early spring, continuing to grow for six months until ovulation occurs in early October, when the young female is about 21 months old.
Of the lizards examined, the smallest containing fully mature ova within the ovaries was 54.0 mm from snout to vent. The gestation period is 12 to 13 weeks, and so the females give birth to their first young at the end of their second year.
Text-fig. 3 illustrates the seasonal changes in the external appearance of the ovary following and preceding ovulation. The collapsed follicles are visible immediately after ovulation as large white flat oval sacs, each with a medium longitudinal scar. However, a week or so after ovulation the collapsed follicles become smaller, compact and disc-like, 2.0 to 3.0 mm in diameter, and slightly yellow as the corpus luteum forms within the follicular cavity. The scar on the follicle becomes less obvious being seen as a discontinuity in the general texture of the luteal mass. The corpora lutea persist until parturition occurs, some regression taking place as the diameter diminishes to average 1.5 mm (range 1.0 to 1.75 mm) during December and January. Regression following parturition is rapid, for save for one female with corpora lutea 1.5 mm in diameter which was killed immediately after giving birth to six young, no non-gravid females showed traces of corpora lutea.
The ovaries are at their minimal mass from just after ovulation until after parturition, this being the gestational period when the average weight of the ovary is 2.0 to 4.0 mm. From October until March the resting ovary shows no great change of mass, and contains 2 to 3 corpora lutea 1.5 to 3.0 mm in diameter, 2 to 5 ova approximately 1.5 to 2.5 mm in diameter and seven to eight smaller ova less than 0.75 mm in diameter. In March the larger ova, generally two or three but up to five in an ovary, begin to enlarge, becoming more turgid and a deeper cream colour than the other ova. As the deposition of yolk proceeds the ova become 4.0 to 5.0 mm in diameter by late June (the middle of the hibernation period), the ovaries weighing between 49.0 and 115.0 mgm at this time. By early October, when ovulation occurs the individual ova have reached 5.0 to 6.5 mm in diameter. The weight of a mature ovum is from 75 to 115 milligrams, and the ovary may weigh more than 200 milligrams, depending upon the number of mature ova that it contains. The seasonal changes in the mass of the ovaries based on 44 mature or maturing lizards is shown in Text-fig. 4; the small figure alongside each point plotted indicates the size group to which the lizard belongs. Some correlation can be seen between the size of the lizard and the absolute mass of the ovaries, there being a general tendency for larger lizards to have heavier ovaries. The commonly used index “mass of ovaries as a percentage of body weight” has not been used here as the varying amounts of tail loss and regeneration in the specimens examined does not allow reliable comparisons to be made upon such a basis.
Table II shows the number of ovulations that occurred (as evidenced by corpora lutea within the ovaries), or the number of maturing ova, in 32 individuals. The total number of mature ova produced by any one lizard varies from two to eight, and the number is the sum of an even or uneven number of ova from each ovary. In twenty animals the same number of ova were produced by each ovary.
Twenty-three of the twenty-six lizards had either 2 or 3 mature ova in each ovary. Thus the potential total number of ovulations was 4, 5 or 6 in over 80 per cent of the lizards examined, eleven having 4 ova, six with 5 ova, and nine
Text-fig. 3.—1–6—Seasonal changes in the external appearance of the left ovary of Leiolopisma zelandica from a series of adult females. 1, October ovary, shortly after ovulation, showing corpora lutea; 2, February ovary prior to parturition, corpora lutea persistent; 3, March ovary; 4, April ovary; 5, June-July ovary; 6, September ovary, preovulatory. 7. Gravid adult female, 60.0 mm from snout to vent, dissected to show 7 ova within the oviducts. 8. Immature ovary and oviduct of a sub-adult female 52.0 mm in snout-vent length, April. 9. Left ovary and oviduct of adult female, June. 10. Left oviduct of an adult female 61.0 mm long in October containing 3 ova, just after ovulation. Three collapsed follicles are present in the ovary. 11. Oviduct and left ovary of an adult female immediately after parturition, February. Abbrev.: O, ovarian follicles; CL, corpora lutea; AL, alimentary tract; OV, oviduct; K, kidney.
Text-fig. 4.—Records of the ovary weight as an average for both ovaries for 45 specimens of Leiolopisma zelandica. The small figure alongside each record indicates the size-group to which the lizard belongs, as follows: 1. 21.0–25.9 mm in snout-vent length. 2. 26.0–30.9 mm in snout-vent length. 3. 31.0–35.9 mm in snout-vent length. 4. 36.0–40.9 mm in snout-vent length. 5. 41.0–45.9 mm in snout-vent length. 6. 46.0–50.9 mm in snout-vent length. 7. 51.0–55.9 mm in snout-vent length. 8. 56.0–60.9 mm in snout-vent length. 9.61.0 mm and above in snout-vent length.
|Total Number of Mature Ova.||Number of Lizards.||Distribution of Mature Ova or Corpora Lutea Between Ovaries.|
|Left Ovary.||Right Ovary.||Number of Lizards.|
with 6 ova. From the middle of October to January, the season of birth, with only one exception all females examined that were 54.0 mm or more from snout to vent, were gravid. Gestation therefore is about three months, and does not appear to vary appreciably. As another set of follicles begins to enlarge two or three months after parturition and are ready to rupture six months later, each mature female is able to bear young each year. The above data are summarised in Text-fig. 6, where they are shown in relationship to that of the male cycle.
It is usual for the ova in each ovary to pass into the oviduct on the corresponding side. However, one female was collected which had three ova in each oviduct with two corpora lutea in the left ovary and four in the right. Another lizard was found to have three collapsed follicles in each ovary and two ova in the left oviduct and four in the right. In both cases it can be concluded that an ovum had made a transabdominal passage to reach the oviduct. Weekes (1927) records a specimen of Lygosoma (Hinulia) quoyi with a damaged oviduct in which all of the ova from one side passed to the opposite oviduct. The instances described for Leiolopisma zelandica show the transfer from one side to the other of only one of a number of ova released by the ovary concerned. This may indicate that the ova are released into the body cavity to pass into the oviduct rather than that the funnel actively clasps the ovum in the ovary.
Not all of the ova released develop within the oviducts; in three of the eight gravid females collected fewer ova were found within the oviducts than would be expected from the number of collapsed follicles present in the ovaries. Two lizards had one less ovum in each oviduct than the number of corpora lutea in the corresponding ovaries. One large adult female had 4 and 5 corpora lutea in the right and left ovaries respectively, 3 ova in the right oviduct with well developed embryos, and 5 ova in the left oviduct, but only three of these containing embryos. In two of these cases the number of ovulations at 7 and 9 were higher than is usual. No atiesia of ova within the ovaries was seen; apparently all the mature ova are ovulated.
On passing into the oviducts the ova become elongate, 6.5 to 9.5 mm long and 5.0 to 7.5 mm wide, and lie close to one another in the oviduct, which is expanded but forms a continuous chamber rather than a series of pouches. The right oviduct is still longer than the left. In eight gravid females the left oviducts contained a total of 19 ova and the right oviducts 24. Fully formed embryos unpigmented except for the eyes were found in mid-December, with the surrounding yolk approximately equal in mass to the developing embryo. A gravid female killed in mid-January contained five full-term embryos in all respects no different from newly-born young, accompanied by little or no yolk.
Two lizards were found to have retained within the oviducts embryos that had been arrested in their development through some unknown cause. One of these, a female collected on March 14, 1954, and examined after preservation, had within the otherwise empty oviduct a badly preserved mass 6.0 mm long containing an embryo, the whole forming a single pouch-like expansion of the closely investing oviduct. The second lizard, captured on October 19, 1954, had each oviduct distended by three recently ovulated ova. A vesicle on the right oviduct was connected to it by a narrow neck of tissue. The vesicle contained a well formed embryo, flattened into a concave disc and unaccompanied by yolk. The vesicle was pressed by the right oviduct against the dorsal wall of the body cavity. In this position it had not impeded the passage of the recent ova. Both of these embryos were obviously retained from a previous breeding season.
During gestation the inguinal fat bodies lying posteriorly in the body cavity central to the kidneys and oviducts and lateral to the rectum and bladder undergo reduction in size. The fat bodies of females at the beginning of hibernation in April are discrete and leaf-shaped, 7.0 to 13.0 mm long, 4.0 to 6.0 mm wide and 1.0 to 2.0 mm thick, pale yellow, semi-translucent, and of an oily nature due to
the large number of small oil globules they contain. At the end of hibernation the fat bodies are not obviously reduced in size, being still firm, uniform in thickness, well defined in outline, and persisting unchanged until ovulation. In gravid females the fat bodies become diffuse and thin, forming a discontinuous sheet of the usual general outline and dimensions but the oil distributed in small patches or elongate nodules. Female lizards two weeks before, or after, parturition either lacked fat bodies entirely or showed only a trace of fat within the associated connective tissue.
Sixteen specimens of Leiolopisma aeneum (Girard) obtained on various dates from Pukerua Bay, Wellington, show considerable differences in the reproductive pattern from that of L. zelandica. Twelve specimens of L. aeneum contained maturing ova in the ovaries or ova in the oviducts, distributed as follows:
Eight lizards had a single large ovum in each ovary or oviduct.
Two showed a single large ovum in the right ovary and two ova in the left.
One had two mature ova in the right ovary and none in the left.
One lizard collected on September 22, 1955, had one ovum in the right oviduct and one mature ovum in the left ovary.
In three other specimens also taken on September 22, ovulation had already taken place. Thus in L. aeneum generally one ovum matures in each ovary, and ovulation occurs at least two weeks earlier than in L. zelandica. L. aeneum is a smaller skink than L. zelandica, inhabiting a few restricted coastal regions and islands adjacent to Wellington. The adults rarely exceed 55.0 mm from snout to vent, as against L. zelandica, which reaches a maximum size in the Wellington district of about 64.0 mm. A female L. aeneum 45.0 mm in snout-vent length
Text-fig. 5.—Records of the testes weight as an average for both testes for 26 specimens of Leiolopisma zelandica and 6 specimens of Leiolopsima aeneum. The black circles indicate that sperm was present in the epididymis of the individual concerned. The small figure alongside each record refers each lizard to its size-group as follows:—1. 21.0–25.9 mm in snout-vent length 2. 26.0–30.9 mm in snout-vent length. 3. 31.0–35.9 mm in snout-vent length. 4. 36.0–40.9 mm in snout-vent length. 5. 41.0–45.9 mm in snout-vent length. 6. 46.0–50.9 mm in snout-vent length. 7. 51.0–55.9 mm in snout-vent length. 8. 56.0–60.9 mm in snout-vent length. 9. 61.0 mm and above in snout-vent length.
collected in April had a single large ovum 2.0 mm in diameter in each ovary, indicating that the females mature at a smaller body size than those of L. zelandica.
Twenty-six male Leiolopisma zelandica and six male Leiolopisma aeneum were examined, ranging in size from 25.4 mm to 62.0 mm. Each animal was killed immediately after capture. The testes were measured and the general appearance of each testis, epididymis and vas deferens noted. The testes were then excised and weighed separately. In order to determine the presence or absence of sperm, a portion of the left epididymis was teased apart, stained lightly with aqueous methyl green for two minutes, mounted in water and pressed beneath a cover-slip to spread the material in a thin layer. Sperm could readily be seen in this preparation.
The testes of Leiolopisma are like those of most lizards, being paired oval white bodies suspended on either side of the body cavity by the mesorchia, the right testis lying more anteriorly than the left. The winter testis of adult males captured in June or July is from 3.5 mm to 4.5 mm long, and 1.90 mm to 2.75 mm wide, weighing 2.0 to 8.0 milligrams, and when fresh is pale, wrinkled and flaccid. The epididymis is dorso-lateral to the testis and appears as a compact body 3.5 mm to 4.5 mm long and 1.5 to 2.0 mm wide. Each vas deferens passes back across the mid-ventral surface of the kidney to the cloaca, to open separately close to the urinary duct. In preserved specimens the testis has a yellowish-brown tinge, the epididymis appearing as a snowy-white structure in strong contrast to the black-pigmented peritoneum.
A moderately developed epididymis permitted ready recognition of two juveniles 26.0 mm and 35.0 mm from snout to vent, as males, even though their testes were no different in appearance from the ovaries of immature females; but usually the sex of lizards below 35.0 mm cannot be decided even by dissection, since there is
little difference in the appearance of the male and female gonads and ducts until towards the end of the juvenile males' first hibernation.
The smallest lizard with sperm in the epididymis, collected on July 21, 1954, and 45.5 mm in snout-vent length, was by estimate at least 18 months old. Two other lizards 49.0 mm collected in October, and 46.5 mm collected in November, were not mature. In general, males were at least 51.0 mm from snout to vent before sperm was found in the epididymis. This size is attained towards the end of their second summer before hibernation, when the skinks are by estimate 16 to 17 months old and as no growth occurs in this period the probable time of maturity is on emergence from hibernation when the skinks are 20 to 21 months old.
The adult winter testes range in size from 3.5 mm to 4.5 mm long, 1.9 mm to 2.75 mm wide and 2.0 to 8.0 mgm in weight. The testes of adult animals in the summer months are from 4.0 to 5.5 mm long, 2.2 to 4.25 mm wide and 8.0 to 32.0 mgm in weight. Thus the testes of adult lizards are less in weight and size, particularly in diameter, during the winter months.
Text-fig. 5 shows the testis weight as an average for both testes, for twenty-five specimens of Leiolopisma zelandica and six Leiolopisma aeneum, plotted against the time of the year. The testes are at their minimal mass during June and July, the middle of the hibernation period. Collections during September and October contained too few males to establish the exact time of increase in testis mass, though skinks collected in September and October showed that there is some increase in testis size and weight. From January to April the testes averaged greater in weight than testes from lizards collected during the hibernation period.
From January to June the males 51.0 mm or more in snout-vent length contained sperm within the epididymis. In July, two large adult males contained no sperm, one only a small amount, and three other lizards abundant sperm. Only six lizards, four of which were sub-adult, were examined in September, October and November, and none of these showed sperm in the epididymis, although the testes were of mature size. Text-fig. 6 gives the overall picture of the male cycle, and its relation to the female cycle.
Copulation would be expected to occur at the time of, or shortly after, sperm production in the males and about the same time as ovulation in the females. Ovulation takes place in the first weeks of October, a time which apparently does not coincide with the presence of sperm in the epididymis of the males, as shown in the graph (Text-fig. 5), though it does appear to coincide with a rapid increase in testis size. Copulation has not been observed in the field, and the only copulation seen occurred between two lizards held in the laboratory on March 28, 1955. The attitudes assumed in copulation are shown in Text-fig. 7. The copulating lizards were two of eight that had been caught some 48 hours previously, and placed in a glass trough prior to release, and the copulation may have been a displacement activity, the product of the close confinement and the abnormal conditions to which the lizards were subjected. However, as both this observed copulation and the presence of abundant sperm in all males at this time could indicate that copulation takes place in the late summer, smears were taken from the vents and oviducts of the females collected for the next five months, from early April to late August. No sperm was found in any of these smears, but as they were made from preserved material the results cannot be regarded as conclusive.
From the above data it can be seen that examination of male lizards does not allow the time of copulation to be precisely determined. Either copulation occurs about the time of ovulation in the females, thereby coinciding with the rapid seasonal increase in testis mass, or else copulation precedes hibernation and females retain sperm until ovulation in the following spring, as do certain salamanders (Stebbins, 1954).
Female skinks are not known to retain sperm for lengthy periods before ovulation. Studie on Eumeces fasciatus by Fitch (1954) and Eumeces septentrionalis
by Breckenridge (1943) have shown that copulation occurs after the animals emerge from hibernation and that the eggs are laid only a few weeks later. In both of these lizards there is a definite enlargement of the testes in the early spring, similar to that in L. zelandica. However, no data is available on sperm production in Eumeces and the significance of sperm within the epididymis in relation to the time of copulation is not yet determined.
No growth study of any member of the genus Leiolopisma has yet appeared. However, the growth rates of several species of the scincid genus Eumeces have been determined by the use of two main methods. Taylor (1936) briefly discusses growth in the genus Eumeces on the basis of a fairly large series of museum specimens which he sorted into age-size groups, concluding that members of the genus required as long as nine or ten years to attain adult size. Breckenridge (1943) marked all the individuals in a small colony of Eumeces septentrionalis in Minnesota, and Rodgers and Memmler (1943) made large “year round” collections of Eumeces skiltonianus near Berkeley, California. Both of these skinks were found to reach mature size (65.0 mm) at the end of their second year, E. septentrionalis breeding in the following spring and E. skiltonianus at the end of its third year. Fitch (1954) showed that Eumeces fasciatus reaches small adult size in the growing season following its first hibernation and becomes sexually mature when about 20 months old, and that Taylor's age groups were artificial, for there is much overlapping in size, even between the two more or less distinct age groups present.
Although E. septentrionalis, E. skiltonianus and E. fasciatus belong to separate groups within the genus Eumeces, the two former species resemble one another in their growth pattern and in the time they take to reach maturity, but E. fasciatus is notably different in its more rapid growth and the shorter time it takes to reach sexual maturity.
Leiolopisma zelandica resembles Eumeces fasciatus in its rapid rate of growth and early maturity.
In the present study, growth has been investigated by measuring and then releasing as many young and adults as possible, some of which were recaptured to provide growth records. The marking programme was carried out in the study area close to the University, from the end of May, 1954, until September, 1955, during which time two hundred and twenty-two lizards were marked and measured.
The period of the study included only one breeding season, and the majority of the animals marked were of adult size. Thus it has not been possible to follow the growth of an individual lizard from birth to adult size; however, sufficient information has been obtained from the 61 lizards recovered at least once to indicate the general pattern of growth. Table III presents the number of captures and recaptures, the greater number of lizards being taken in the summer period between the hibernations of 1954 and 1955.
|No. of Animals Marked and Measured.||No. of Lizards.||Total No. Of Lizards Recaptured.||Total No. Of Captures.|
|Caught Once.||Caught 2 Times.||Caught 3 Times.||Caught 4 Times.||Caught 5 Times.||Caught 6 Times.|
As indicated in a previous section, parturition in 1955 took place from early January to early February, the majority of the young being born in the last week of January Some variation in the period probably exists between different years and in any one year within separate parts of the reptile's range.
A series of 19 newly-born young captured over three days at the peak of the parturition period averaged 0.276 gm weight (range 0.18 to 0.40 gm) and 27.6 mm long from snout to vent (range 24.5 mm to 29.0 mm). Six young born to one female in captivity averaged 0.265 gm (range 0.18 to 0.40 gm) and 24.8 mm long from snout to vent (range 24.5 mm to 25.0 mm).
The most rapid growth occurs in the weeks immediately after birth; for example, a lizard (No. 118, Table IV) captured soon after birth when 25.0 mm long, showed an average gam of 0.17 mm and 0.007 gm per day over a period of 50 days. Two other juveniles (Nos. 87 and 95, Table IV) averaged 0.15 mm and 0.14 mm per day respectively in snout-vent growth, and No. 87 gained 0.007 gm per day in weight, but No. 95 showed no weight increment. Another juvenile (No. 93, Table IV) marked soon after birth at a snout-vent length of 25.5 mm was recaptured 243 days later in the following spring when 37 5 mm in length and three and a-half times its former weight. The slight increase in length of only 2.0 mm for this lizard, when compared with No. 87, which was first marked on the same day at the same snout-vent length but recaptured after only 68 days at a length of 35 5 mm, indicates that the initial rapid growth does not extend over the hibernation period. One lizard (No. 79, Table IV) was 29.5 mm in snout-vent length when captured on January 29, 1955, and on recapture 35 days later it was 38 5 mm. It can be assumed that this lizard was of average size when born, and from this it can be estimated that the time of birth was probably in the first week of January, so that its size on entering hibernation would be at least 45.0 mm. The size range of juveniles entering their first hibernation is from 30.0 to 45.0 mm, with most lizards between 35.0 and 40.0 mm.
|Animal No.||Date 1955.||Snout-vent length in mm.||Tail length in mm.||Weight in grams.||Remarks.|
|118||Feb. 2||25.0||28.0||0.4||8.5 mm snout-vent length; 5.0 + mm tail length; 75% weight increase in 50 days. Capture points 45ft apart.|
|Mar. 24||33.5||33.0 (tip lost)||0.7|
|87||Jan. 26||25.5||15.5 + (stump)||0.3||Showing rapid growth of lizard and marked as newly-born young, only a few days old. 10.0 mm snout-vent length; 17.0 mm tail, weight increase × 2⅔ in 68 days. Captures 30ft apart.|
|Apr. 6||35.5||25.5 + 7.0||0.8|
|93||Jan. 26||25.5||29.0||0.29||Captures 50ft apart. 12.0 mm snout-vent length; 13.0 mm tail growth; weight increase × 3⅓. Compared with No. 87 in text. Marked only a few days after birth.|
|Sep. 29||37.5||42.0 + (tip lost)||0.99|
|95||Jan. 27||26.0||31.0||0.3||2.5 mm increase in snout-vent and tail length in 18 days. No appreciable weight increase. Captures 10ft apart. Newly-born skink.|
|79||Jan. 21||29.5||34.0||0.46||Points of capture 10ft apart. Rapid growth of very young lizard caught and marked soon after birth. Discussed fully in text. First captured 2 weeks after birth.|
|Animal No.||Date.||Snout-vent length in mm.||Tail length in mm.||Weight in grams.||Remarks.|
|196||1955||25 mm snout-vent growth, no weight increase in 54 days. Slow growth of yearling during hibernation period.|
|12||1954||Little growth during hibernation period. Slight weight increase. Tip of tail lost on revovery. But very large amount of regenration for young animal. Capture sites 3 feet apart.|
|Jun. 22||38.0||7.5 + 22.0||0.8|
|Aug. 18||38.0||7.5 + 21.0||1.0|
|127||1955||Points of capture within a 6 feet radius. 4.0 mm snout-vent growth; 7.0 mm tail growth; 15% weight increase; in 65 days to April 6. No growth over hibernation period.|
|78||1955||Loss of weight shown; animal carrying young on January 20. Taper of tail almost perfect, regeneration difficult to assess. Captures within a 12 feet radius.|
|Jan. 20||58.0||54.5 + 6.0||4.0|
|Mar. 28||59.0||58.0 + 3.5||3.0|
|Jul. 18||59.0||58.0 + 3.5||3.2|
|Oct. 22||59.0||58.0 + 3.5||3.5|
|6||1954||All captures within a 3 feet radius. Note slow growth of tail during hibernation period then rapid increase in rate. Regeneration 7 mm in 70 days (Aug. 2-Nov. 9).|
|May. 24||58.0||25.0 + 6.0||3.4|
|Aug. 2||58.0||26.0 + 5.0||3.3|
|Aug. 17||58.0||26.0 + 5.5||3.2|
|Nov. 9||58.5||26.0 + 12.5||3.4|
|135||1955||Captures within a 6 feet radius. No growth during hibernation period.|
|Mar. 3||60.0||57.0 + 7.0||4.6|
|Mar. 7||60.0||57.0 + 7.0||4.4|
|Mar. 22||60.0||57.0 + 7.0||4.0|
|Mar. 25||60.0||57.0 + 7.0||-|
|Aug. 29||60.0||57.5 + 7.0||3.3|
|140||1955||Capture points the same each case.|
|Mar. 7||62.0||16.0 + 28.0||3.9|
|Mar. 22||62.0||16.0 + 28.0||3.6|
|206||1955||Capture points 19 feet apart.|
|Jun. 16||63.0||14.0 + 27.0||4.0|
|Nov. 1||63.0||14.0 + 27.0||4.0|
|Animal No.||Date||Snout-vent Length in mm.||Tail length in mm.||Weight in grams.||Remarks.|
|37||1954||Approx. 9 months old when first caught. 14.0 mm snout-vent length; 21.0 mm tail growth; 64.6% weight increase; in 165 days from Sep. 22, 1954 to Mar. 7, 1955. Captures within a 10 feet radius.|
|31||1954||Lizard probably about 20 months old at first capture. 7.5 mm snout-vent growth, 80% weight increase; in 224 days. Recaptured 30 feet from point of first capture.|
|Sep. 2||48.5||33.5 + 17.0||1.9|
|Apr. 4||56.0||38.0 + 10.5 (tip lost)||3.4|
|127||1955||First captured when about 1 year old. 4.0 mm snout-vent growth; 7.0 tail length; 15% weight increase; in 65 days (to April 6, 1955). Capture points within a 6 feet radius.|
|41||1954||7.0 mm tail growth; 4.0 mm snout-vent length; 40% weight increase; in 35 days. Rapid growth following first hibernation. Captures within a 6 feet radius. Lizard about 9 months old when first captured.|
|Oct. 19||36.0||16.5 + 14.5||0.7|
|Nov. 23||40.0||17.5 + 20.5||1.0|
|50||1954||Rapid growth in early summer 2.0 mm snout-vent length; 3.5 mm tail length; growth in 23 days. Capture points 7 feet apart. About 9 months old.|
|Anima No.||Date||Snout-vent length in mm.||Tail length in mm.||Weight in grams.||Remarks.|
|59||1954||4.5 mm snout-vent growth, 8.0 mm tail growth in 133 days. No growth during hibernation.|
|103||1955||Probably 2 years old at first capture 4.0 mm snout-vent length, 2.5 mm tail length in 44 days (Jan. 26-Mar. 11, 1955). Captures within a 5 feet radius.|
|Jan. 26||50.5||9.5 + 25.0||2.0|
|Mar. 11||54.5||10.0 + 27.0||2.4|
|Nov. 12||57.0||11.0 + 27.0||3.25|
|67||1954||5.0 mm snout-vent growth, 6.5 mm tail growth in 98 days. Captures within a 10 feet radius.|
|Nov. 29||52.0||13.0 + 29.0||3.7|
|Mar. 7||57.0||14.5 + 34.0||3.6|
|Mar. 22||57.0||14.5 + 34.0||3.3|
|22||1954||All captures within a 6 feet radius. Period of at least 15 days before tail regenerated. 11.0 mm tail regeneration in 104 days (Aug. 17-Nov. 29).|
|Oct. 19||55.5||11.0 + 3.0||2.9|
|Nov. 1||55.5||11.0 + 7.0||2.7|
|Nov. 12||55.5||11.0 + 9.5||3.0|
|Nov. 29||57.0||11.0 + 11.0||3.3|
|39||1954||22.0 mm tail regeneration; 5.0 mm snout-vent length; 30% weight increase; in 97 days. Recaptured within 2 feet original capture site.|
|Oct. 17||55.0||9.0 + 9.0||2.7|
|Feb. 1||60.0||9.0 + 31.5||3.5|
|51||1954||7.0 mm snout-vent length; 20.0 mm tail growth; 25% weight increase in 104 days; summer growth.|
|Feb. 14||62.0||9.0 + 21.0||3.0|
|54||1954||5.0 mm snout-vent growth; 20% weight increase. Points of capture 7 feet apart.|
|Nov. 15||56.0||12.0 + 33.0||3.0|
|Aug. 29||61.0||12.0 + 20.0 (tip lost)||3.7|
|14||1954||All captures within an 8 feet radius. 20.0 mm tail regeneration in 259 days (June 21, 1954 to March 7, 1955).|
|June 21||58.0||36.0 (no reg)||3.3|
|Nov. 23||58.0||36.0 + 5.5||3.9|
|Mar. 7||60.0||37.5 + 20.0||4.5|
|17||1954||Captures within a radius of 10 feet. 3.0 mm snout-vent growth; 4.0 mm tail growth; in 312 days. No growth during hibernation period. Tail fully regenerated.|
|July 7||60.0||6.5 + 28.0||3.2|
|Mar. 15||63.0||5.5 + 33.0||3.5|
|Mar. 28||63.0||5.5 + 33.0||3.1|
|Oct. 21||63.0||5.5 + 33.0||3.4|
|Nov. 12||63.0||5.5 + 33.0||3.3|
|8||1954||3.0 mm body growth; 2.0 mm tail growth; 0.3 gm increase in weight; in 376 days. Captures in successive hibernation periods, only 2 feet apart.|
|May 27||62.0||26.0 + 26.5||4.7|
|July 7||65.0||27.5 + 27.0||5.0|
|30||1954||Gravid female, 1.7 gm increase in weight in 97 days, abdomen width increased from 11.0 mm to 15.5 mm in same period. Captures 3 feet apart.|
|Aug. 18||66.0||24.0 + 27.0||5.0|
|Nov. 23||68.0||23.5 + 28.5||6.7|
Text-fig. 9.—Records of growth in all the individual skinks marked and subsequently recaptured one or more times. The figure alongside certain of the records refers to the detailed recapture data in Tables IV (Juveniles), VI (Sub-adults) and VII (Adults).
There is little or no growth of the lizards during hibernation as shown from measurements of a small number found while hibernating (Text-fig. 8; Table V). This period is not included in the graphs showing the growth rates of marked animals subsequently recovered. The length of the hibernation period omitted is based on the observed activity of the lizards within the study area.
The young lizards reach adult size 50.0 mm in snout-vent length during their second summer following their first hibernation. Very few young lizards were caught and only one recovery after a long term was made (No. 37, Table VI). This lizard averaged 0.085 mm per day increase in snout-vent length and 0.009 gm per day increase in weight for 165 days between hibernations, and reached an adult size of 51.0 mm when about 16 months old. Three other short-term recoveries (Nos. 41, 50 and 127, Table VI) showed similar trends in growth, respectively averaging 0.11, 0.087 and 0.062 mm per days increase in snout-vent length.
It is not clear whether the small number of sub-adult lizards captured was due to the few young surviving from a previous unrecorded breeding season, or to their more secretive habits. The lizards reach adult size over the brief span of 3 to 4 months in the first half of their second season of growth, and in these, the months of October, November and December, the vigorous plant growth of early spring provides much concealing cover which does not allow the young lizards to be readily caught.
The different growth rates of both the juvenile and sub-adult lizards leads to the loss of identity of the age-size groups as some of the lizards approach small adult size. Overlapping in size may occur between lizards 14 to 16 months old and individuals with retarded growth a year older. A rapidly growing juvenile (such as No. 79, Table IV) could attain a length of 45.0 mm at the end of its first season of growth, and be at least 55.0 mm long by the end of its second season of growth, when two years old. The group of lizards marked when about 55.0 mm in snout-vent length (Nos. 22, 51, 39, 67 and 54, Table VII) could include one or more lizards that reached large sub-adult size in their first season of growth. Despite the possible overlap these are in the main lizards in their third season of growth from 19½ months to 27 months old. The lizards above 55.0 mm in snout-vent length, that show a much slower rate of growth (Nos. 14, 17, 8, Table VII) are in their fourth season of growth, being 31½ to 39 months of age.
The average rates of growth of lizards for successive size increments has been calculated from all the recoveries shown in the graph (Text-fig. 9), and are presented in Table VIII. As the size group 55.0 to 59.9 mm includes lizards in both their third and fourth (and perhaps fifth) season of growth, two different rates of growth are evident. The averages for this size class have been calculated separately and as for other size classes the hibernation period of four and two-thirds months has been subtracted where necessary from the time elapsed between captures. The growth rates for each size class include those of some individuals that were recorded as growing through one or more size classes between captures which may produce inaccuracies in the average rates recorded.
The average growth rates are graphed in Text-fig. 10, together with a small number of individual recoveries which illustrate typical growth trends in relation to the calculated average. In order to obtain the time in months that it takes for a lizard to grow through a particular size class, the average monthly increment in millimetres for the lizards of a particular class was divided into the total increment within the size class. The periods of growth and hibernation with the sizes at different ages are included to provide a general picture of the growth of L. zelandica.
|Size Group (snout-vent length) in mm.||Average Growth per Month in mm.||No. of Skinks in Sample.||Total Growth Recorded in Sample in Months.||Remarks.|
|25.0–39.9||4.11||4||9⅔||Juveniles before first hibernation.|
|35.0–44.9||3.30||3||4¼||Sub-adult lizards in second growth season.|
|45.0–49.9||1.53||4||7½||Sub-adult lizards in second growth season.|
|50.0–54.9||1.50||10||20||Small adult lizards to 22 months of age.|
|55.0–59.9||0.76||15||36½||Overall average for size class.|
|1.33||7||17½||Adults 22–26 months in third growth season.|
|0.24||8||19||Adults in at least fourth growth season.|
|60 & above||0.28||11||41||Large adults of indeterminate age.|
Text-fig. 10.—The average growth rate for successive size increments in Leiolopisma zelandica based upon the records of the skinks marked and subsequently recaptured. The unbroken lines accompanied by a number are individual recoveries (Tables IV, VI and VII) included to show typical growth trends in relation to the calculated averages (Table VIII).
Some lizards may fail to reach adult and breeding maturity by the time of emergence from their second hibernation. No direct evidence of this was obtained; the growth trend of one short term recovery (No. 50, Table VI) indicates that this lizard may have been no more than 45.0 mm long on entering its second hibernation. Individuals differ in their rate of growth, some continuing to grow rapidly until above average adult size and others ceasing rapid growth when below average adult size. The time of birth is critical in that it decides the maximum size that the
lizard reaches before entering its first hibernation. Similarly an extended autumm, allowing a longer first growth season, would show itself in later years by the presence of larger than average adults within any one age class which could only be separated from older lizards by their faster rate of growth.
The age-size classes of the population of L. zelandica studied (as represented by the average growth rates of those lizards recaptured) are thus not distinct from one another. The only readily identifiable group are lizards in their first year less than 46.0 mm in snout-vent length. A typical lizard (based upon the average rates of growth for successive size increments) attains 35.0 mm in snout-vent length at the commencement of its first hibernation when two and a-half months old. Growth ceases during hibernation and in its second growing season the juvenile reaches 45.0 mm at the end of one year and 50.0 mm at fourteen and a-half months of age, at which size the lizard enters hibernation for the second time. In the third growth season the lizard reaches 55.0 mm in snout-vent length when about twenty-two months old. Above 55.0 mm two rates of growth are apparent, the faster growing lizards being adults in their third season of growth, and the slower growing animals adults four or more years of age. The average rates of growth for lizards of these two ages which mix within a single size group are calculated separately. A few individuals may reach 60.0 mm in length by their 26th month, but in general the lizards do not exceed 60.0 mm until they are at least 34 months of age. The lizards mature sexually after their second hibernation, when above 50.0 mm in snout-vent length and at about 20 months of age.
The weights of all the lizards handled from the study area, either once or as recoveries, are plotted against their snout-vent lengths in Text-fig. 11. The relation
between body weight and size is by no means uniform, as the varying amounts of tail loss and regeneration affect the bodyweight by as much as 18 per cent. Gravid females may be 30 per cent. above their normal weight just before parturition, the weight increase being in direct proportion to the number of young carried.
The average weight of the young at birth is 0.25 gm (range 0.18 to 0.40 gm), and the juvenile lizards enter hibernation three months later when 35.0 to 40.0 mm long, averaging 0.94 gm (range 0.65 to 1.65 gm), increasing in weight by three and one-third times in the first season of growth.
In the second growth season the young lizards increase in length to 45.0 to 50.0 mm, weighing on the average 2.28 gm (range 1.95 to 3.5 gm), thus multiplying their weight by two and two-fifths times. Thereafter the increase in weight is no more than 20 per cent. in any one season of growth. Lizards less than 55.0 mm in snout-vent length rarely exceed 3.5 gm, and those between 55.0 mm and 60.0 mm long 4.5 gm. The maximum weight recorded was 6.6 gm for a very large gravid female 65.6 mm long, just prior to parturition.
Growth and Regeneration of the Tail
The relative length of the tail varies considerably even among lizards that have never lost their tails. Also during the course of growth of the young lizards to sub-adult size the relative proportion of the tail changes. Text-fig. 12 shows the relative tail length (as a percentage of snout-vent length) in skinks of different size groups with undamaged tails.
At birth (20.0 mm to 25.0 mm from snout to vent) the tail length averaged 110.5 per cent. of the snout-vent length. In larger young from 31.0 mm to 40.0 mm the tail continues to grow more rapidly than the body, averaging as much as 126 per cent., which is greater than the average length of either smaller or larger lizards. The average tail length of lizards 45.0 mm to 55.0 mm in snout-vent length was less, averaging 123 per cent., and a small number of lizards 56.0 mm to 60.0 mm averaged 113.0 per cent. No sexual dimorphism was evident in this feature from the data available.
Of some 274 lizards handled in the field or laboratory 179, or 65.8 per cent, had recently broken or regenerated tails. A freshly broken lizard's tail loses almost no blood; only a few small drops are seen to ooze from the irregular surface of the exposed concave muscle masses of the tail stump. The detached portion with its protruding muscle masses may continue to writhe for several minutes. At room temperature of 17.6° C. a newly broken section of tail 21.0 mm long lashed violently from side to side for 95 seconds. Rolling and twitching continued with decreasing magnitude for a further 85 seconds, then voluntary movements ceased. At the end of eight and a-half minutes contractions and brief twitches could still be induced by touching the tail, and severe stimulation elicited slight twitches at the end of thirty minutes.
A scab forms across the newly-broken stump within a few hours; the surrounding scales which project slightly beyond the point of the break fold inwards to form a smoothly rounded stump. Since no lizards were seen with infected tail breaks the conclusion that some prophylactic mechanism operates can be drawn. When the scab is lost the healed surface of the break is covered with a convex, smooth black skin, finely granular in texture (Text-fig. 14). No further growth occurs for a week or two, then regenerative growth proceeds rapidly, the sharply tapering new growth being of less diameter than the old tail at the point of break. A dull black skin of silky texture with no signs of scales, covers the regenerating tail whose tip is bluntly rounded Scale formation does not occur until the length of the regenerated portion approaches two-thirds of its ultimate length, which is generally less than that of the old tail. Such scale formation is seen as a series of concentric ridges arising at the old overlapping scales and gradually spreading towards the tip of the tail. The colour and form of the regenerated tail do not match those of the old tail. The new scales are coloured a dull orange dissimilar to any other
colour on the skink's body and instead of two scale rows in the mid-dorsal and mid-ventral region of the tail, single large scales form equal in width to two ordinary scales. In a fully regenerated tail the new scalation merges evenly into the old, often obscuring the original break which can be detected only by its dull orange colour and different scale pattern.
Large adult lizards may possess tails with three or more sections each set off from the other by a slightly different angle of taper, as the regenerated portion is also capable of regrowth when broken. Breaks in the tail occur at the mid-point of a single vertebra and not intervertebrally, a cartilaginous rod replacing the vertebrae in the regenerated portion
Fitch (1954) points out that the rate of growth of the regenerated tail depends upon the age, condition and activity of the individual together with the position of the actual break. If a young lizard loses its tail early in life it is possible for the length of the regenerated tail to be greater than that of the old tail. The regenerated tail of adult lizards rarely attains the length of the original; the absolute length reached depends upon the position of the break. The closer the break is to the vent the longer the length of the regenerated tail, but the likelihood of the regenerated tail reaching the length of the old tail becomes less. The proportion of original and regenerated tails of 179 lizards are plotted in Text-fig. 15. Lizards which have a stump of the old tail equivalent to 20 per cent of their snout-vent length at the maximum regenerate a length equal to 65 per cent of their snout-
Text-fig. 12.—Diagram showing relative tail length (as a percentage of snout-vent length) in skinks of different size-groups that retained their original tails unbroken. The relative increase in tail length in the early stages of growth is apparent, the trend being reversed before adult size is reached. The mean, standard error, standard deviation and range for each size-group is shown.
vent length; the total tail length at 85 per cent of snout-vent length is considerably less than that of unregenerated tails which in adult lizards average 113 to 123 per cent of snout-vent length (Text-fig. 12).
In skinks with the original tail equal to 40 per cent of the snout-vent length, the fully regenerated tail may reach 107 per cent of the snout-vent length; and in those with stumps 60 per cent of the snout-vent length the completely regenerated tail may reach 113 per cent of the snout-vent length. Lizards which have a length
Text-fig. 13.—Diagram showing the relative length of the tail stump (as a percentage of the snout-vent length) in skinks of different size-groups that have at some stage lost their tails. There is an apparent trend for larger (and older) lizards to have less of their original tail. The mean, standard error, standard deviation, and range is shown for each size-group.
of old tail equal to 80 per cent or more of their snout-vent length may regenerate enough tail length to restore the tail to its former length (Text-fig. 15). The skinks measured included many with incompletely regenerated tails, which accounts for the wide range of variation shown. The completely random scatter of the proportions of the original tail shows that there is no tendency for the tail to break at a particular point. Breaks occur at any point along the tail length, being unusual only close to the vent; generally a length of old tail at least equal to 10 per cent of the lizard's snout-vent length remains. Larger and older lizards lose a greater portion of the original tail probably due to successive tail breaks, although the complicating factor of increase in torso length with age may enhance this effect (Text-fig. 13).
The growth rate of the regenerating tail is rapid following the initial healing period, which lasts two or three weeks. The fastest rate of regeneration recorded amongst 20 individuals (Text-fig. 16) was 1.13 mm per week in a lizard whose tail regenerated 21.5 mm in 132 days The record marked “A” on the graph is the most complete one obtained from a lizard with a recently broken tail The tail stump of this lizard was freshly healed at the first capture, the amounts of regeneration for 5 successive captures were 15th day after first capture, no regeneration;
Text-fig. 14.—The successive stages of tail regeneration in Leiolopisma zelandica. (1–7 are drawn to the same scale) 1. Stump of a freshly broken tail showing protruding muscle masses and the scales overlapping the actual point of break. 2. The exposed surface of the tail portion lost in 1. 3. The healed surface of the tail stump about 2. weeks after loss The overlapping scales have folded inwards over the wound. 4. First stage of tail regeneration about 2. weeks after regeneration commenced. 5. Regenerated portion before scale formation commences. 6. Incipient scale formation. 7. Regenerated tail with fully formed scales of a different shape to those of the original tail. 8. Fully regenerated tail. The discontinuity shown at the mid-point of the regenerated portion is produced by secondary regeneration of a once regenerated tail.
Text-fig. 15.—Relative lengths of original and regenerated portions of tails in skinks which have had their tails broken and regenerated; for each individual the length of the regenerated portion and the original portion is separately expressed as a percentage of the snout-vent length.
47th day 3.0 mm; 58th day 7.0 mm; 69th day 9.5 mm and 86 days after the first capture 11.0 mm of tail was regenerated. The changing rate of growth is followed by a period of rapid growth which gradually slows as the regenerated tail approaches its final length. Skinks with a substantial portion of tail already regenerated showed only a slow increase in tail length of as little as 1 mm in 7 months.
The tail is lost as the result of mechanical damage of some description. No skink of the hundreds handled during the course of the study dropped its tail when handled with normal care. A blow, a sudden jerk or pinching of the tail, is necessary before a length is detached. Leiolopisma zelandica can be lifted and even restrained by the tail, and as long as there are no sudden pulls the tail will not be dropped. When the skink is attempting to escape in the field there may be a condition set up in the animal that facilitates tail loss if the lizard is grasped by the tail. The tail is used as a storage organ for fat, and the usually round tail becomes emaciated and square in cross-section in lizards deprived of their normal food supply. One lizard that lost a previously unregenerated tail close to the base at capture suffered a decrease in total weight of 18 per cent. Thus the loss of the tail may involve the loss of a considerable amount of stored fat.
During the study period from March, 1954, to October, 1955, moulting was first observed in a lizard captured on October 19, 1954, which shed its skin in a laboratory cage. The slough was completed in 24 hours from the onset, the newly exposed epidermis having an iridescent sheen which still persisted when the animal was released two days later. Five other lizards captured in the following five weeks showed varying degrees of slough, the last being taken on November 29, 1954. Others captured in this period had the typical sheen of new skin, signifying a recent moult.
In all the lizards observed shedding followed a fairly well defined pattern. The scales of the ventral surface of the head and body, the flanks and the dorsal surface of the neck extending back to above the forelimbs, are the first to be lost. The epidermis flakes off in the form of transparent scales corresponding to the underlying osteoderms, scales being lost in irregular patches, singly or in sheets of several dozen that cling loosely together. Next the epidermis of the ventral surface of the tail, the upper parts of the limbs and the dorsal surface of the body are shed. Then the scales covering the head shields and the lower parts of the limbs are lost, so completing the slough In contrast to the rest of the animal the epidermis of the manus and pes is cast off in the form of a complete “glove” which rolls back on itself until it is sufficiently loose to be rubbed off in the course of normal movement. The sloughed-off epidermis frequently remains only as an anklet or wristlet after the rest of the moult has been completed.
Moulting appears to be restricted to about a six-week period extending from mid-October to the end of November. One skink captured on January 18, 1955, had the sheen usually associated with a recent moult, and the period may not be as brief as indicated above. As the process is rapid in a healthy skink, and can be completed in 24 hours, it is not surprising that it was observed on relatively few occasions.
Feeding Habits and Food
In this study skinks have been seen feeding on only a few occasions in the field as their secretive habits prevent ready observation. L. zelandica is diurnal and vision possibly plays a considerable part in the detection and selection of suitable food. The gastrointestinal content of the skinks examined consisted mainly of terrestrial arthropods.
Both juvenile and adult skinks select actively moving prey in preference to stationary food animals even though the moving insect may be the more distant. Several times both in the field and the laboratory skinks have been seen to investigate suitable food which was finally rejected when the lizard failed to stimulate the food animal into activity.
The gastrointestinal contents of 68 specimens of L. zelandica were examined. Two-thirds of the specimens were collected at points within a radius of ten miles from the study area, with the exception of 18 specimens from Pukerua Bay and four from Stephens Island. All the specimens were killed immediately after capture; however, four from York Bay that were received some days after capture had empty stomachs.
The specimens represent seven localities each with a slightly different range of ecological conditions and microhabitats. Accordingly the analysis of the stomach contents of the groups from each place are presented separately in Table IX to bring out any local differences in food habits. Seventeen specimens of L. aeneum from Pukerua Bay were also examined, and some appreciable differences are apparent between the food of this species and that of L. zelandica.
As each skink was dissected the entire alimentary tract was removed, placed under water in a watch glass, and the stomach and intestinal contents examined separately. Complete insects were rarely found, some parts being lost or digested more rapidly than others and the remainder present as a felted mass of legs, abdomen segments, fragments of thorax chitin and head capsules. Soft bodied animals such as coleopteran and lepidopteran larvae were not found below the stomach. The prosoma of spiders, chitinous insect appendages, head capsules and wings, persisted unchanged down to and in the rectum.
Faecal pellets were not found in the field, and no attempt has been made to examine scat material. The typical pellet is a small elongate cylindrical mass 2.0 to 3.0 mm long by 1.5 mm wide, almost invariably capped at one end with a chalky mass of uric acid.
A summary of the material identified from all the specimens examined is presented in Table IX. The individual animals composing the food were not identified beyond ordinal rank.
Of the 68 specimens of L. zelandica examined, 12 (17.6 per cent) had completely empty alimentary tracts. None of these skinks was taken in hibernation, and all the specimens of L. zelandica captured in the winter months contained some food. None of the 17 specimens of L. aeneum was captured whilst in hibernation, and 5 contained no food remains.
The average number of food items per lizard for 9 specimens of L. zelandica taken in the hibernation period was 3.77, contrasted with an average of 5.03 items per lizard for 61 lizards captured in the summer months. Even though the rates of digestion are probably slower in the winter months, the presence of some food in the stomachs of lizards collected in June and July indicates that intermittent feeding may occur during hibernation, which agrees with the finding given later that hibernation is often interrupted and not continuous.
A total of 297 food items, an average of 5.47 items per lizard, were collected from L. zelandica alone, and of these, 217 were insects, 80 arachnids and 75 terrestrial amphipods or isopods. The prey ranged in size from small mites less than 1.0 mm long to a single large lepidopteran larva 21.5 mm long by 4.5 mm which entirely filled the distended stomach of one individual. Normally the food was less diverse in its size range, generally consisting of food items 1.0 mm to 6.0 mm long. Perhaps the most unusual food was from an adult female 53.0 mm long collected on the seashore of Island Bay, Wellington, on March 1, 1954, which contained 63 mosquito larvae, 2.0 mm long. This skink was captured within 30 yards of a number of brackish splash zone pools a few feet above high tide level which contained
|Food Organisms||Orthoptera||Hemiptera||Coleoptera||Lepidoptera||Diptera||Hymenoptera||Thysanura||Pseudoscorpionidea||Dermaptera||Amphipoda||Isopoda||Araneida||Acarina||Unidentified Arthropod Material||Mollusca||Nematoda||Plant Material||Males||Females||Number of Lizards|
|Pukerua Bay No of Organisms||1||16||4||4||4||1||-||1||-||7||12||10||21||-||-||24||-||8||10||18|
|Frequency - No Lizards||1||6||5||4||4||1||-||1||-||3||4||6||5||5||-||4||6|
|Brooklyn Wellington Organisms||4||11||8||2L||6||-||-||-||3||8||14||14||-||-||1||13||-||7||13||20|
|Kelburn Wellington Organisms||1||18||10||1L||-||4||-||-||-||9||5||2||4||-||-||15||-||5||7||12|
|Island Bay Wellington Organisms||7||17||2L||2L||67||10||-||-||-||1||9||10||10||-||-||9||-||-||7||7|
|Stephens Island Organisms||1||4||11||1||7||2||1||-||-||1||5||6||2||-||-||11||-||1||3||4|
|Somes Id Wellington Organisms||-||2||-||-||1||1||-||-||-||4||-||1||-||-||-||2||-||2||1||3|
|York Bay Wellington Organisms||-||-||-||-||-||-||-||-||-||-||-||-||-||-||-||32||-||-||4||4|
|Totals Food Organisms||14||68||37||7L||85||18||1||1||3||30||45||43||37||-||1||106||-||23||45||60|
|Frequency - No Lizards||10||24||18||18||14||10||1||1||1||17||19||27||9||20||1||24||11|
|Frequency as a percentage of total lizard sample||14 9||35 3||26.5||26 5||20 6||14.9||1 5||1 5||1 5||25.0||27 9||39 7||13.2||29 8||1 5||35 3||16 5|
|Frequency - No Lizards||-||7||-||-||2||2||-||-||-||2||2||1||6||3||-||-||-||7||10||17|
|Frequency as a percentage of total lizard sample||-||41 2||-||-||11 8||11 8||-||-||-||11 8||11 8||5 9||34.5||17 7||-||-||-|
many thousands of larvae of the mosquito Opifex huttoni which breeds in salt water. The number of Diptera recorded in Table IX is thus abnormally high and is not typical of the food of the lizard.
Aside from small particles of soil, other non-animal inclusions were mainly plant material such as small pieces of leaves, grass stems and seeds. The seeds may have been taken as food, for in all cases they were too large to have been swallowed accidentally and could hardly have accompanied other food. Two skinks from Pukerua Bay contained single large dark-brown seeds 4.5 × 2.0 mm and 3.5 × 1.75 mm, of plants of the family Polygonaceae, and two other lizards from the same locality each contained another large unidentified seed 6.0 × 3.0 mm and 4.0 × 2.5 mm All the seeds were hard and undigested There was no material of any description in the gastrointestinal contents that indicated cannibalism or the eating of slough.
The largest variety of food found in any one animal was recorded from an adult female L zelandica 60.0 mm long, collected from Stephens Island on December 18, 1954 The detailed list is as follows, the figure in parentheses being the largest dimension of the food item in millimetres stomach, 2 dipteran flies (5.0), 1 adult beetle (4.5), 1 beetle larva (3.0), 1 hemipteran (4.0), 1 small piece vegetable matter (3.0), 4 large wood lice (5.0, 4.0, 4.0, 3.0), 1 thysanuran (6.0); intestine, 3 Hemiptera (7.5), 3 beetle heads, 1 woodlouse, 3 heads Diptera, 1 moth (3.5); rectum, 3 Coleoptera (elytra only), 2 Hymenoptera (5.0), and the heads of 1 orthopteran insect and 1 dipteran fly. This lizard was unusual in that 8 different orders were represented in its food, when generally arthropods belonging to 1 to 4 different orders comprised the food of any one animal.
Many of the Hemiptera, Lepidoptera, Diptera and Arachnida appeared to be of the kinds usually found amongst herbaceous vegetation. The terrestrial amphipods and isopods which form a major portion of the skink's food (in bulk as well as numbers) are plentiful in dank and humid surroundings beneath rotting vegetation, logs and stones. The range of food found in the gastrointestinal contents of the species indicates that L. zelandica forages in many parts of its environment, preying upon the arthropodan fauna of all levels from that found in its shelters to that of the herbaceous vegetation of its home range. The most important food organisms of the species in order of the frequency of occurrence are: spiders and hemipterans, followed by isopods, coleopterans, lepidopterans and amphipods in almost equal frequency.
The food of Leiolopisma aeneum is similar in some respects, hemipteran insects and spiders constituting the bulk of the food items found However, there are two marked contrasts in the absence of any coleoptera or lepidoptera, which may either point to differences in the feeding habits of L. aeneum or reflect differences in the microfauna of its environment.
Slightly more than one-third of the specimens of L. zelandica examined were infected with a parasitic nematode identified as Pharyngodon sp. (order Oxyuroidea). This short stout nematode about 4.0 mm long was found in the rectum. No nematodes were obtained from Leiolopisma aeneum.
Only two previous studies of the movements of skinks have been made, these being by Goin and Goin (1951) on Eumeces laticeps and Fitch (1954) on Eumeces fasciatus Fitch reports that Goin and Goin found that E. laticeps has a well defined territory, each adult excluding other adults from its home territory but tolerating young, and each lizard centering its activity around some convenient shelter that forms a home base. In contrast E. fasciatus is not territorial in its behaviour and has no regular home base; tending to limit its activities to a small area, wandering little. Studies by Newmann and Patterson (1909), Fitch (1940) and Stebbins and Robertson (1946) on three different species of the iguanid genus
Sceloporus have shown that the individuals of the species tend to keep to well defined areas, with territorial behaviour well developed. Numerous other studies on reptiles, particularly turtles and snakes, have demonstrated the presence of home ranges generally much larger than those of lizards.
The individuals of L. zelandica wander little, centering their activities about a small area, even smaller than Fitch records for E. fasciatus. Territoriality does not appear to be developed to any extent, and individual home ranges may overlap with the home ranges of one or several other lizards.
The information on the movements of L. zelandica has been gathered from the capture of marked individuals. No detailed records over a specific time are available for a single individual skink and the pattern of the movements in relationship to time and their possible causes are unknown. A skink may have wandered considerable distances between captures, including the very periphery of its home range, and recaptures must represent only a portion of the lizards' total range. Direct observations on the movements of L. zelandica are precluded by the nature of the environment which obscures the skink during its moves. The available evidence points to naturally delimited routes of approach and retreat from certain areas such as basking places.
The position of each skink, marked or unmarked at capture, was recorded in relation to a named reference point, there being no lack of suitably distinct landmarks within at the most ten feet of the capture site. The skinks were released at precisely the same point after weighing and measuring in the laboratory. The elapsed time between successive captures varied from one day to 14 months, and although recoveries less than one month apart were rarely of value in determining growth rates, the short term recoveries were often the most useful for assessing home ranges.
Fitch (1954) assumes “.… that any two successive captures of the same individual separated by a substantial time interval will be distributed at random to each other within the area to which the animal's activities are confined. The varied techniques of capture by hand and with different types of traps would help to secure random distribution of the capture sites. If the home range were covered uniformly by the animal in the course of its activities, any two random capture sites would be on the average separated by a distance equal to half the home range diameter. If the animal tends to concentrate its activities in the central part of the home range as seems to be the case the capture sites will be correspondingly closer together”. The same basis as that used by Fitch is assumed in assessing the significance of the distances between captures Two-thirds of the lizards captured were taken by hand, which assures the random nature of capture site distribution. The average distance between captures for 21 lizards (excluding juveniles in their first year) captured only twice, was 6 feet (range 0 to 23 feet), which indicates that the size of the home ranges of L. zelandica in the study area is relatively small.
The greatest distance between successive captures was 50 feet, for a juvenile marked 8 months previously, and the least movement in terms of time was that of a lizard taken by trap or hand 5 times in 6 months at the same place. The average distance between captures for 45 adults in 75 moves was 5.9 feet (range 0–18 feet), and for 8 sub-adult lizards 9.4 feet in 13 moves (range 0–32 feet). Six juveniles in their first year were recaptured an average distance of 24.5 feet from the marking site (range 6–50 feet). The longest moves recorded occurred in the juvenile lizards in their first few months preceding hibernation.
All the juveniles recovered in their first year were recaptured only once after marking, and so their home ranges cannot be delimited. Two juvenile skinks were recaptured within 6 feet of their first capture after 24 and 30 days, whereas the three longest moves by juveniles (Nos 87, 118 and 93, Table IV) of 30, 45 and 50 feet were after periods of 68, 50 and 243 days respectively. The first pair of juveniles may have already established a range when first caught and others moved in search of suitable home ranges during the period between captures.
The dispersal phase occurs in the juveniles, for not only were their moves the longest ones recorded, but they were almost invariably captured whilst moving across the surface carpet of dry grass far from cover in the form of stone or concrete slabs. The behaviour of the young is quite distinct in this respect, for the adult skinks are rarely found far from immediate cover.
The short distances between the captures of sub-adult and adult lizards indicates that these lizards have regular home ranges.
Table X gives the distances between successive recoveries for all adults, which are divided into three groups with regard to the time of marking and recapture;
|Adults: No. of Captures, Sexes not separated.||Average Distance in Feet Between Point of Capture and Extremes for All Moves.||Average Maximum Distance in Feet Between Points of Capture.||No of Skinks in Sample.||Time of Year.|
|Individuals captured just twice||4⅓ (0–9)||4⅓||9||Marked and recaptured in summer between hibernations.|
|Captured 3 times||6⅓ (0–19)||10||7|
|Captured 4 or more times||2⅘ (0–10)||5⅔||5|
|Individuals captured just twice||93/4 (8–18)||93/4||4||Long term recoveries, including both hibernation and summer period.|
|Captured 3 times||6¼ (0–18)||10||8|
|Captured 4 or more times||7½ (0–18)||16||3|
|Individuals captured just twice||1¼ (0–5)||1||7||Lizards marked and recovered within a single hibernation period.|
|Captured 3 times||2½ (0–5)||5||1|
|Captured 4 or more times||2½ (0–5)||5||1|
the lizards marked and recovered in a single summer between hibernations; the long term recoveries including both the summer and part of the hibernation period; and those found two or more times whilst in hibernation.
The calculated averages are based upon recoveries representing individual home ranges, for no definite changes of range were recorded. The average home range diameter of 18 feet obtained for all adults (with the exception of those in hibernation) is calculated from the average maximum distance between captures. The actual area of such a home range would be approximately 15 square yards.
The home ranges of lizards caught a sufficient number of times to allow the shape and size of their home ranges to be determined, are given in Text-fig. 17, 18 and 19. The letters enclosed in a circle on each of these text-figures relates the particular portion of the study area figured to the plan of the whole area (Text-Fig. 2).
The detailed record of each skink whose home range is figured can be found in the preceding section on growth, with the exception of lizards Nos. 59, 74 and
Text-fig.. 18.—Successive capture sites for another group of skinks also on Station B, and recorded in the same period as those shown in Text-Fig. 19.
159 which are presented below. The individual records for the home ranges in Text-fig. 19 are not detailed since the majority of these lizards were captured in the same narrow area during hibernation. The sex of the lizards where determined has been indicated on the figures.
Lizard No. 59. Three captures in ten months, on October 24, 1954, on April 5, 1955, 30 feet from the first capture site; trapped once more on September 29 within 10 feet of the first capture site. This lizard shows the largest single home range of any recovered, and was just below adult size when first captured (48.75 mm) and of adult size (53.5 mm) when recaptured for the first time.
Lizard No. 74. Large adult female 62.0 mm long. Taken twice in January in the same trap. Carrying young on January 17, 1955. Parturition occurred within the 10-day period. Trapped twice more in another trap 8 feet distant on March 7, and 22, 1955.
Lizard No. 159. Large adult female 64.0 mm long. Marked just before hibernation on March 10, 1955, recaptured in the same trap on November 15, 1955, and trapped 4 feet away 7 days later.
The size of the adult home range does not vary greatly and no difference in size is apparent between the home ranges of adult males and females. The home ranges of lizards No. 37 and 59 (Text-fig. 17) are larger than the average adult range, the distance between their successive captures being a little more than one and a-half times that of the adults. Both of these lizards were sub-adults when first captured, and were recaptured as adults. Thus the largest single home range recorded was that of a sub-adult lizard, No. 59, which was captured in two successive summers at points 10 feet apart and found hibernating in the intervening winter 25 feet from its nearest other capture. The longest extension of this lizard's home range area was toward the basking area marked in Text-fig. 17 and 18.
The overlapping of the home ranges is well illustrated in Text-fig. 17 and 18. The home ranges shown in these figures were obtained from lizards captured concurrently in the area (Station B, Text-fig. 2) and have been separated to avoid overcomplicating the diagrams.
The shape of a lizard's home range appears to be modified according to the nature of the plant cover and physical features of the environment. Most of the home ranges figured are triangular in outline, which is due in part to the fact that many were based on three different points of capture.
The study area contains many terraced portions separated from each other by concrete walls of varying heights, and moderate grassy slopes. The skinks travel along the natural pathways at the base of these walls, moving vertically up the surface of the walls where their surfaces are sufficiently rough. They follow regular escape routes which are decided by the nature of the terrain, moving directly ahead when disturbed, passing up and then down any obstruction in their path if they cannot escape by any other means. The home range may include two or more levels separated by a wall, usually with a fissure or overhanging mass of vegetation by which the lizard passes from one level to another. Leiolopisma zelandica has been observed to launch itself down and across small gaps up to 10 inches wide even when moving about undisturbed. Tree climbing has not been seen; however, two instances were recorded of a skink climbing amongst the dense heads of fennel (Foeniculum vulgare) between 2 and 3 feet above the ground.
No definite change of range was recorded for any lizard marked and recaptured in the study area, even though it contained the home ranges of a large number of lizards. Any shifts of range may have taken the lizard concerned outside the limits of the study area. Despite frequent searches extending many hundreds of feet outside the study area, no marked skink showing a change of range was found, all the lizards captured being unmarked. Some of the unmarked skinks captured in the study area, especially late in the marking programme, may have entered the area from the surrounding ground.
Skinks shift their ranges through various causes, one at least being interference with the surrounding environment. Twenty-six were captured and marked in one small area (Station A, Text-fig. 2) thirty feet in diameter. The vegetation about the area was cut and trimmed by a party of workmen who burned the resulting plant debris within a few yards of the capture site. Not one of the 26 lizards has since been taken, although a few unmarked lizards were captured within the same general area after several months had elapsed. Station A thus suffered frequent human interference, and the few home ranges recorded in this area (Text-fig. 19) area of lizards which changed cover during hibernation with some moves in the following summer. Very small, well-defined home ranges may be maintained by lizards that are undisturbed. Several skinks never captured have been observed inhabiting the same concrete ledge or brick heap throughout the study. One of these lizards, readily recognisable, has been seen basking on one particular ledge on numerous occasions over an eighteen month period, eluding all attempts at capture by escaping down a crevice only a few inches from its basking place.
Thus individuals of L. zelandica tend to remain within small areas which are their regular home ranges. These ranges are generally about 15 square yards in extent, being modified in size and shape according to the individual and its position in the area. In the study area the abundant plant cover, the concealment available in the form of numerous crevices under concrete walls and slabs, the plentiful food and wide distribution of basking places, allow the skinks to fulfil all their needs within a small area. The home ranges of two or more individuals may overlap. Groups of lizards congregate in the basking places, tolerating each other and showing no signs of territorial behaviour. The home ranges of adult females and males do not apparently differ in size or shape. The sub-adult lizards may have slightly larger home ranges than the adult skinks. The greatest distances between successive captures were those recorded for juvenile skinks in their first year in the dispersal phase that occurs in the few months preceding their first hibernation.
The Wellington district is not subjected to severe winter temperatures, the frosts are infrequent and light, and the ground is never frozen. Consequently L. zelandica is not forced to resort to the deep burrowing into the earth typical of some species of hibernating skinks in the higher latitudes of the northern hemisphere (Breckenridge, 1943). The relatively mild local climate does not induce the complete suspension of activity in all members of the skink population, for skinks whose winter refuges are exposed to the sun on warm winter days may emerge to bask. The study area was inspected at least once every fine day during winter when there was any likelihood of skinks coming out to bask, and the pit-traps were left open throughout the winter of 1955. Lizards were not taken in the traps during the winter months, indicating that most lizards remained in hibernation. However, on July 7, 1955, a warm sunny day, a single skink was seen basking on a concrete ledge sheltered from the prevailing cold southerly wind and close to a heap of damp and decomposing vegetation. When caught as it attempted to seek concealment under a stone protruding from the heap of plant debris, the skink was still warm to the touch. This skink may have sought other shelter on release as it was not retaken in subsequent searches of the area. McCann (1955) records L. zelandica as emerging to bask on warm days during the winter months.
The marking programme was commenced a few months after the beginning of the 1954 hibernation period, and all the skinks captured in the first few months of the marking programme were in hibernation. A solitary lizard was seen basking on August 18, 1954, after a few days of warm weather, which were followed by several days of cold wet weather. Then on August 30, 1954, many lizards were seen basking, the population remaining active for the rest of the spring and the summer. The activity of the population declined once more in the first two weeks
of April, 1955. As only seven more skinks were trapped in September, a particularly wet month, the general emergence from hibernation may have been delayed. Thus the hibernation period is approximately four and a half months long, extending from the middle of April to the end of August.
Cover is so abundant in the study area that no lizard would need to move far in order to find a suitable winter refuge. The few recoveries made during hibernation show that any moves at this time are generally confined to a single piece of cover, although the lizard may move to other shelter if disturbed too often, as several skinks found hibernating on two or more occasions subsequently moved to other resting places. The lack of difference between the size of the home ranges of lizards captured only in the summer months and those marked or recaptured during hibernation and retaken in the summer months indicates that the skinks seek a place to hibernate within their home range areas. Text-fig. 19 shows the movements of a group of skinks captured one or more times during hibernation, and the average distances moved for all skinks captured when in hibernation are included in Table X.
Fitch (1954) points out that the lizards' habitat may be scarcely recognizable from the lizards' point of view when it emerges from hibernation. The changes that take place in the area studied are primarily in the density of the herbaceous vegetation. The dry, low-lying vegetation of late summer and autumn is replaced by a vigorous growth of grasses and weeds, in particular onion-weed (Allium triquetrum) and fennel several feel high. Such growth differences, Fitch maintains, may promote changes of range brought about by the dramatic changes in the microhabitat. None of the skinks captured in successive summers were recorded as changing their range, and the effect of the seasonal changes in the plant cover upon the lizards cannot be assessed.
The relatively mild climate of the Wellington area does not induce the deep hibernation characteristic of skinks found in regions with more severe climates. Food was found in the alimentary tracts of some specimens taken in the middle of the hibernation period, and several skinks whose hibernation sites were more likely to be exposed to the direct warmth of the winter sun were observed basking during this period. Thus hibernation is not always complete in L. zelandica, and certain individuals may emerge to bask and feed in a period when the remainder of the population is comparatively inactive.
Escape Reactions and Predators
Lizards of the family Scincidae are generally secretive, relying on their ability to seek concealment rather than speed or aggressive behaviour to escape their enemies. Leiolopisma zelandica is no less secretive than the other members of the family, and it invariably seeks cover at the slightest danger.
The behaviour of the newly-born lizards renders them more conspicuous than the adults. In the period immediately following parturition in January, the greatest activity occurred in the lizard population. At this time as many as 40 newly-born young were caught when moving across patches of short grass far from the type of cover favoured by the adult. The behaviour of these juveniles is characteristic of animals in the dispersal phase, and probably results in a higher mortality rate amongst the juveniles than the adults. This is borne out in part by the numbers of young found with damaged tails, for 21.9 per cent of the 51 juveniles captured before their first hibernation had broken or regenerated tails. An overall percentage of 65.8 of the 274 lizards captured during the study had broken or regenerated tails.
Leiolopisma zelandica can often be detected by the rustling of leaves as it moves undisturbed beneath the herbaceous vegetation, and the noise may on occasions indicate the skink's position to predators. When disturbed the skink immediately seeks shelter beneath suitable cover, and often the first sign of their presence is a fleeting glimpse of a moving brown form. Once in adequate cover the skink does
not retreat far, and remains close by until the danger has passed, when it resumes its former position. Many times during the study skinks were captured by waiting quietly beside the spot where they were last seen.
Protective colouration aids L. zelandica in its concealment. The drab straw brown of the lizard's upper surface, dark-brown flanks and longitudinal light coloured stripes, blend well with many backgrounds. However, L. zelandica has not been seen to “freeze” in the presence of danger as does Eumeces fasciatus (Fitch, 1954). Leiolopisma zelandica differs from the skinks of the genus Eumeces in that the adults become only slightly darker with age and retain the basic colour pattern of their youth, also the adult males do not assume a conspicuous breeding colouration. The more conspicuous colour phases found in the genus Eumeces are thus not present in L. zelandica which tends to make the latter species less conspicuous to predators.
The natural enemies of L. zelandica are not well known. Wodzicki (1950) in a discussion of the food of the wild cat (Felis domesticus), notes that, “Various species of lizards are favoured by cats …” The extent of the predation by cats on the species was well illustrated towards the beginning of the study when a mass of recent vomit containing the remains of six L. zelandica was found on a path adjacent to the study area. The bodies of these skinks showed numerous small puncture marks probably made by the teeth of a cat, and undoubtedly constituted a single meal.
Oliver (1955) describes the following birds as feeding upon “lizards”: the red billed gull (Larus novaehollandae scopulinus), the morepork (Ninox novaeseelandeae novaeseelandeae), the harrier hawk (Circus approximans), the bush hawk (Falco novaeseelandiae), the kingfisher (Halcyon sancta), the pukeko (Porphyrio melanotus stanleyi) and weka (Gallirallus australis). Each of these birds constitutes a predator only in certain parts of the lizard's range. The kingfisher is probably the most widespread enemy of L. zelandica; Oliver (1955) records Guthrie-Smith as noting that lizards sometimes form the main diet of this bird. Kingfishers were seen in the study area on four occasions, but were not seen taking lizards. A number of introduced birds such as the black backed magpie (Gymnorhina hypoleuca) and the starling (Sturnus vulgaris vulgaris) may feed on lizards, but the habit is not recorded in the literature.
Seventeen species of scincid lizards have been described from the New Zealand region, and with one exception all belong to the genus Leiolopisma. As no other detailed studies have been conducted on the New Zealand Scincidae, few comparisons can be made between species on the basis of the present study.
The number of head plates of L. zelandica was examined and found to be constant except for the upper and lower labials and the nuchals. The number of scales round the mid-body and the number of subdigital lamellae under the 4th toe of the hind-limb were counted in 50 specimens in an effort to test the constancy of specific characters. The ratio snout-forelimb length to axilla-groin length varied from 1.2 to 2.0 (2.0 +) in the 50 specimens of L. zelandica examined. McCann (1955) gives this ratio at 1.0 + to 1.5 based upon the examination of at least 40 specimens. The higher ratio was the product of a slightly larger sample, taken from a single district, whereas McCann's specimens are the equivalent of a number of small samples from the total range of the lizard. The character is in no way critical in the diagnosis of the species and in other respects the measurements and scale counts agree with those given by McCann (1955).
In recent years ecological and life-history studies have been made in North America on several oviparous skinks of the genus Eumeces by Rodgers and Memmler (1943), Breckenridge (1943), and Fitch (1954). As L. zelandica is viviparous its
reproductive pattern shows few similarities with the genus Eumeces. However, L. zelandica resembles at least one of the Eumeces species in its pattern of growth.
Two main differences were found to exist in the reproductive pattern of L. zelandica and L. aeneum. The small sample of L. aeneum examined averaged only two ovulations per female, and L. zelandica was found to give birth to 3 to 5 young each year. L. aeneum is a smaller lizard than L. zelandica, becoming sexually mature at about 45.0 mm in length. It is not clear whether the difference in the number of young is an effect of the smaller size or of genetic and ecological factors. The females of L. aeneum were found to have ovulated two weeks earlier than L. zelandica in 1955.
Fell (1948) recorded three observations of viviparous reproduction in New Zealand skinks assigned by him to the genus Lygosoma. Two specimens of Leiolopisma moco gave birth to single young, one in February and the other in March, 1946, and another skink Lygosoma (Leiolopisma) smithu gave birth to young in March. Fell does not state where the specimens were collected, but if taken south of the 38° S. parallel it was most probably Leiolopisma zelandica. Therefore parturition may not always occur at the same time each year or in successive years, as parturition occurred in the skink population of the study area in January and early February, 1955.
In view of the differences in the number of young recorded within the genus Leiolopisma, the degree of placentation, and the time of parturition, the life history of L. zelandica cannot be held to be completely typical of the rest of the genus in New Zealand.
The gestation period of L. zelandica is at least three months. The only gestation period reported for a viviparous scincid is that of Lygosoma (Hinulis) quoyi which is approximately three months. The iguanid Leiolaemus multiformis multiformis carries its young for 5 to 7 months (Pearson, 1954) and in Xantusia vigilis gestation was found to be for three months. The gestation period in L. zelandica does not seem to be unduly long for a lizard.
Fitch (1954), who studied a large population of Eumeces fasciatus, determined from marked and recaptured individuals that the species reaches adult size and becomes sexually mature when about 20 months old. Similarly, the use of the marking method in this study has shown that L. zelandica also reaches adult size and becomes sexually mature at about the same age as E. fasciatus.
Several methods have been used to study growth in reptiles. Taylor (1936) discussed growth in the genus Eumeces on the basis of a fairly large series of museum specimens which he sorted into age-size groups, deciding that the lizards in the genus required 9 to 10 years to attain adult size. Later Rodgers and Memmler (1943) determined, by collecting large samples during the course of a single year, that Eumeces matured in two years, and Breckenridge (1943) confirmed this by studying a small population of marked animals. Breckenridge also found that skinks held in captivity did not grow as fast as those in the wild.
The age-size groups of L. zelandica (apart from young in their first year) cannot be separated into sub-adult and adult animals except upon the basis of the known growth rate of the individual concerned.
Thus the present study supports the conclusions of Breckenridge (1943) and Fitch (1954) in reaffirming that information derived from the capture-recapture method of studying the growth rates of animals under natural conditions is more reliable than data obtained either from the grouping of apparent age-size classes of a population or from animals reared in captivity.
The new-born young of L. zelandica increase in length by at least 40 per cent and more than double their weight in the first season of growth, and thereafter the rate of growth becomes progressively less. L. zelandica resembles many other species of lizards in its rapid rate of early growth. (Fitch, 1940; Breckenridge, 1943; Fitch, 1954).
Many snakes and turtles have been found to occupy regular home ranges. The home ranges of lizards are less well known, those of the iguanid genus Sceloporus being better understood than any other lizards. Goin and Goin (1951) observed territorial behaviourism in the skink Eumeces laticeps and Fitch (1954) described the movements and home ranges of Eumeces fasciatus finding that defensive territorial behaviour was lacking.
The adults of L. zelandica tend to have small home ranges, but they do not always occupy a set site within the area. The home ranges may overlap and no defensive territorial behaviour is shown. This pattern is similar to that recorded for the skink Eumeces fasciatus by Fitch (1954) and differs from that found in the iguanid genus Sceloporus (Newmann and Patterson, 1909; Fitch, 1940; Stebbins and Robinson, 1946) which occupy specific places in the habitat and show a marked degree of aggressive territorial behaviour.
The new-born young of L. zelandica were found moving in the open more frequently than the adults, and it is not unlikely that predators exact a heavy toll, for very few sub-adult lizards of 9 to 10 months of age were captured in the course of the study. There is the possibility that few young were born in the previous breeding season, but this cannot be demonstrated in the present study. A high incidence of tail loss was found in the young of L. zelandica. Fitch (1954) indicates a similar loss in the young of Eumeces fasciatus and he decided that the mortality rate was high amongst the hatchlings. The few sub-adult lizards captured and the high incidence of tail loss in juveniles of L. zelandica would appear to indicate a high mortality rate amongst new-born individuals. If this is the case, the proportion of the population replaced each year may be slight, particularly in view of the low birth-rate found in the species.
The enemies of lizards in other countries are numerous and include many kinds of snakes, birds, small mammals and even other lizards (Breckenridge, 1943; Stebbins and Robinson, 1946; Lewis, 1951; Fitch, 1940 and 1954). New Zealand has no indigenous snakes, large lizards or predatory mammals, which restricts the lizard predators to a few species of birds and the domestic cat. The effect of a few predators upon the size of skink populations is not known. Nevertheless, decidedly dense populations may be built up in favourable conditions, for 222 individuals were marked within the quarter-acre study area and it is estimated that the population would be at least equivalent to 900 skinks per acre. Fitch (1954) found concentrations of a similar order of density in one particularly favourable habitat of Eumeces fasciatus but generally populations were in the order of 50 to 100 animals per acre. The study-area habitat may not be typical and the optimum conditions present may support a population well above the density as known here.
Summary and Conclusions
1. The common brown skink Leiolopisma zelandica was studied from March, 1954, to October, 1955. The growth, movements and habits of L. zelandica were studied by marking and subsequently recapturing skinks that formed part of a dense population in a small area at Kelburn, Wellington, New Zealand. Skinks were also collected from several other areas in the Wellington district for supplementary data on food and reproduction.
2. L. zelandica is described and tables are given showing the variation in the numbers of certain head plates and body scales based upon an examination of 50 specimens. The number of scales round mid-body, subdigital lamellae, nuchals and upper and lower labials, show slight variation. Other plates are constant. A range of body proportions was found greater than that already described for L. zelandica. The ratio of snout-forelimb against axilla-groin is 1.2 to 2.0. The present status of the species is not affected.
3. The main features of the male and female reproductive cycles of L. zelandica are described from 71 specimens collected over a two-year period. Additional in-
formation derived from 19 specimens of L. aeneum is included. The females and apparently the males also, become sexually mature when about 50.0 mm in snout-vent length and 20 to 21 months of age, following their second hibernation. The females give birth to their first young when two years of age. The males of L. zelandica show no breeding colouration, and the adult males and females (apart from gravid females) cannot readily be distinguished. A seasonal testicular cycle was found to be present in the male, the testes of adults falling to a minimal mass in June and July. The time and duration of testis enlargement was not fully established.
4. Copulation was observed once in the laboratory and is illustrated. Copulation has not been observed in the field and the time that it occurs has not been determined. Leiolopisma zelandica has but one breeding season in each year. The ova develop within the ovaries for 6 months during the winter and spring. Generally 2 or 3 ova develop in each ovary, and all are ovulated in late spring. A corpus luteum forms within the collapsed follicle, persisting until parturition occurs. Gestation requires 12 weeks, and 3 to 5 young are born in midsummer or early autumn. The time of parturition may vary over the range of the species in any one year, and from year to year. Some form of placentation exists in L. zelandica, and the species is truly viviparous. The type of placentation present cannot be determined by reference to that already known to be present in the genus.
5. L. aeneum gives birth to fewer young than L. zelandica. In consequence of this and other differences, the life history of L. zelandica may not be typical of the other members of the genus in New Zealand.
6. The new-born young of L. zelandica average 27 6 mm in snout-vent length, grow rapidly in the late summer, and by the time of their retirement into hibernation they may have increased their weight by two and a-half times and their snout-vent length by approximately 40 per cent. After emergence from hibernation the young continue their rapid growth, and when a year old some may be as large as small adults. In general, however, the young reach small-adult size at the end of their second summer when 15–16 months old, and become sexually mature in the following spring when 20–21 months old. Considerable overlap is found between the age-size classes of sub-adult and adult lizards. The only readily distinguishable size classes are those of young lizards in their first year. Growth continues through-out life. The rate becomes progressively slower in the adults in their third and fourth growth seasons.
7. Most individuals have lost their original tails, and a high percentage of broken tails is found even amongst the young. Two-thirds of all the lizards examined had broken or regenerated tails. After a brief period of healing the tails rapidly regenerate, the regenerated portion bearing different scalation from the original tail. The regenerated tail is rarely as long as the original lost portion.
8. Examination of the gastrointestinal contents of 68 specimens showed that L. zelandica is a predator, feeding almost entirely on small invertebrates. The principal food organisms of the species are, in order of frequency: spiders and hemipterans, with isopods, coleopterans, lepidopterans and amphipods of almost equal occurrence.
9. Slightly more than one-third of the specimens of L. zelandica examined were found to contain a parasitic nematode Pharyngodon sp. (fam. Oxyuroidea) infecting the rectum.
10. The individuals of L. zelandica tend to remain within the small areas which are their regular home ranges. These ranges are generally about 15 square yards, being modified in size and shape according to the individual and its position in the area. In the study area the skinks can fulfil all their needs within a small area. The home ranges of two or more individuals may overlap. Groups of lizards congregate in the basking places, tolerating each other and showing no signs of territorial behaviour. The home ranges of adult females and males do not apparently
differ in size or shape. The sub-adult lizards may have slightly larger home ranges than the adult skinks. The greatest distances (50 feet) between successive captures were those recorded for juvenile skinks in their first growth season. The juveniles form the dispersal phase of the population and establish a home range about the time of their first hibernation.
11. The relatively mild climate of the Wellington area does not induce the deep hibernation characteristic of skinks found in regions with more severe climates. Individual skinks whose hibernation sites are more likely to be exposed to the direct warmth of the sun may emerge to bask and feed. The hibernation period at Kelburn, Wellington, was approximately four and two-thirds months long in 1954 and 1955.
12. Moulting is restricted to a six-week period extending from mid-October to the end of November. The scales are shed in irregularly sized patches and the whole process may be completed in 24 hours.
13. The population in the study area consists of at least 200 animals, and is probably equivalent to a population of 900 skinks per acre. This dense population indicates that particularly favourable conditions for L. zelandica are found within the study area.
14. The natural enemies of L. zelandica are not well known. However, the red billed gull, the morepork, the harrier hawk, the bush hawk, pukeko and weka have been recorded as feeding upon lizards, and these birds take L. zelandica in only certain parts of its range. The most widespread enemies of L. zelandica are the kingfisher (Halcyon sancta) and the cat (Felis domesticus).
I wish to thank all those who have helped in many ways during the course of this study, particularly Professor L. R. Richardson, for his encouragement, advice and willing assistance throughout the whole period. I am also indebted to Mr. W. H. Dawbin and Mr. J. A. F. Garrick for their useful suggestions and help, and to Dr. R. V. Brunsdon for occasional assistance in the field.
Boyd, M. M. M., 1940. The Structure of the Ovary and the Formation of the Corpus Luteum in Hoplodactylus maculatus Gray. Quart. J. Micros. Sci. 82 (2): 337–376.
Breckenridge, W. J., 1943. The Life History of the Black-banded Skink Eumeces septentrionalis septentrionalis (Baird). Amer. Mid. Nat. 29 (3): 591–606.
*Dutta, S. K., 1944. Studies of the Sexual Cycle in the Lizard Hemidactylus flavitridis (Ruppel). Allahabad Univ. Stud. Zool. Sect. 1944; 57–153.
Fell, H. B., 1948. Viviparity in New Zealand Skinks. N.Z. Science Rev. 6 (2): p. 38.
Fitch, H. S., 1940. A Field Study of the Growth and Behaviour of the Fence Lizard. Univ. Calif. Publ. Zool. 44 (2): 151–172.
—— 1954. Life History and Ecology of the Five-lined Skink, Eumeces fasciatus. Univ. Kansas Mus. Nat. Hist. Misc. Publ. 8 (1): 1–156.
*Girard, C. S., 1857. Proc. Acad. Philad.: p. 196.
*Goin, O. B., and Goin, C. J., 1951. Notes on the Natural History of the Lizard, Eumeces laticeps in Northern Florida. J. Florida Acad. Sci. 14: 29–33.
Gray, J. E., 1843. in Dieffenbach, E., Travels in New Zealand, Vol. 2. Fauna of New Zealand. John Murray, London.
Harrison, L. and Weekes, H. C., 1925. On the Occurrence of Placentation in the Scincid Lizard Lygosoma (Leiolopisma) entrecasteuxi. Proc. Linn. Soc. N. S. W. 50 (4): 470–486.
Lewis, T. H., 1951. The Biology of Leiolopisma laterale (Say). Amer. Mid. Nat. 45 (1): 232–240.
McCann, C., 1955. The Lizards of New Zealand. Gekkonidae and Scincidae. Dominion Museum Bull. No. 17: 1–127.
[Footnote] *Not available during the course of this study
Miller, M. R., 1948. The Seasonal Histological Changes Occurring in the Ovary, Corpus Luteum, and Testis of the Viviparous Lizard Xantusia vigilis. Univ. Cal. Publ. Zool. 47 (8): 197–224.
Newmann, H. H., and Patterson, J. T., 1909. Field Studies of the Behaviour of the Lizard, Sceloporus spinosus floridanus. Bull. Univ. Texas. Sci. Ser. No. 15: 1–24.
Oliver, W. R. B., 2nd ed. 1955.New Zealand Birds. Revised and Enlarged edition: 1–661. A. H. & A. W. Reed, Wellington.
Pearson, O. P., 1954. Habits of the Lizard Liolaemus multiformis multiformis at high altitudes in Southern Peru.Copeia 1954, No. 2. 111–116.
Rodgers, T. L., and Memmler, V. H., 1943. Growth in the Western Blue-Tailed Skink.Trans. San Diego Soc. Nat. His. 10: 61–68.
Stebbins, R. C., 1954. Natural History of the Salamanders of the Plethodontid Genus Ensatina. Univ. Calif. Publ. Zool. 54 (2): 47–124.
—— and Robinson, H. B., 1946. Further Analysis of a Population of the Lizard Sceloporus graciosus gracilis. Univ. Calif. Publ. Zool. 48 (3): 149–168.
*Strahl, 1892. Die Ruckbildung reifer Eierstockseier in Ovarium von Lacerta agilis. Verhandl. Anat. Gesellsch. Wien.
Taylor, E. H., 1936. A Taxonomic Study of the Cosmopolitan Scincoid Lizards of the Genus Eumeces with an Account of the Distribution and Relationships of its Species. Univ. Kansas. Sci. Bull. No. 22: 207–218.
Weekes, H. C., 1927. Placentation and other Phenomena in the Scincid Lizard Lygosoma (Hinulia) quoyi. Proc. Linn. Soc. N. S. W. 52 (4): 499–554.
—— 1929. On Placentation among Reptiles. I. Proc. Linn. Soc. N. S. W. 54 (2): 34–60.
—— 1930. On Placentation among Reptiles. II. Proc. Linn. Soc. N. S. W. 55 (5): 550–576.
—— 1934. The Corpus Luteum in certain Oviviparous and Viviparous Reptiles. Proc. Linn. Soc. N. S. W. 59 (6): 380–391.
—— 1935. A Review of Placentation among Reptiles with Particular Regard to the Function and Evolution of the Placenta.Proc. Zool. Soc. London. 1935. 625–645.
Wodzicki, K. A., 1950. Introduced Mammals of New Zealand: 1–255 D. S. I. R. Bull. 98, Wellington.
R. E. Barwick., M. Sc.,
Department of Zoology. Victoria University of Wellington, P. O. Box 196, Wellington, New Zealand.
[Footnote] *Not available during the course of this study.