Art. XLVII.—Notes on Reptiles and Mammals in the Kermadec Islands.
[Read before the Philosophical Institute of Canterbury, 1st June, 1910.]
There are neither land - reptiles nor land - mammals indigenous to the Kermadec Islands, the group presenting in this respect one of the main features of oceanic islands. When the islands were discovered rats were plentiful, but reasons will be given below for considering them as introduced through the agency of man. Two marine animals—the green turtle and the humpback whale—regularly visit the group, while others are occasional visitors.
Mr. R. S. Bell, of Sunday Island, informed me that besides the green turtle one or two individuals of another species, probably the hawksbill, have been noticed from the shore. Mr. T. F. Cheeseman, F.L.S., F.Z.S., mentions a water-snake, which, from the description given him by Mr. T. Bell, he supposes to be Pelamys bicolor (Cheeseman, 1888).
On several occasions during September, 1908, I observed dolphins in Denham Bay, Sunday Island. Mr. Bell says that the sperm whale has been seen from the north coast of Sunday Island. On one occasion a portion, about 2 ft. long, of a large cuttlefish was cast up on Low Flat Beach. This fragment was possibly the remains of an animal which a whale had made a meal from, as it is known that sperm whales kill and eat these gigantic cephalopods.
The following notes are mainly from material gathered during a ten months' stay on Sunday Island, in 1908, as a member of the scientific expedition which originated with Mr. W. L. Wallace, of Timaru.
Chelone mydas. (Green Turtle.)
A large female specimen of the green turtle was shot by Mr. R. S. Bell off the rocks at the south end of Denham Bay on the 23rd May, 1908.
Turtles were noticed chiefly during the summer months—January to March—often as many as five or six being seen at one time. An observer standing on the shore at a little height can watch them browsing on a species of alga (Pterocladia capillacea), which grows abundantly on rocks in water down to about 5 m. in depth. Apparently, whilst in Sunday Island waters turtles eat no other kind of food. Every few minutes they come to the surface for a few seconds to breathe, but on the slightest alarm these timid reptiles swim swiftly away. They do not breed in the Kermadecs, but go north to warmer regions.
Megaptera boops. (Humpback Whale.)
A few humpback whales were noticed in Denham Bay in the latter part of August, 1908. During September their numbers increased, while in October and November they were common all round Sunday Island; at Macauley Island also, on 12th November, a large number were seen. They had their calves with them, and probably were migrating southwards. During their northward migration they are not seen from Sunday Island.
Mus exulans. (Pacific Rat.)
Specimens of the Pacific rat examined on Sunday Island agree in every particular with those from Funafuti, as described by Mr. E. R. Waite, F.L.S. (1897, p. 174), except that the under-surface, including inside of limbs, is light buff, or sometimes pale grey; fur pale grey at base; upper surface of feet light buff, hairs short; hairless parts of feet pink.
Skulls of Sunday Island examples appear to be proportionately more slender than the skull of the Funafuti specimen. The zygomatic arch is less prominent, thus giving a smaller breadth, whilst the nasal bones are narrower. These differences are apparent in the table of measurements given below, where the corresponding figures recorded by Mr. Waite for the Funafuti specimen are given for comparison.
Of thirty-four specimens of rats from Sunday Island of which I have measurements, I select the ten largest of each sex as best showing the size of full-grown individuals :—
|Head and Body.||Tail.||Length of Head.||Ear.||Forearm and Hand.||Hind Foot.|
Thus the male is, on an average, larger than the female. Apparently in the female the tail is proportionately longer than it is in the male; but this is probably due to the fact that the males are the more pugnacious, and consequently have their tails bitten more frequently. A large number of specimens collected for examination had to be rejected because more or less of the end of the tail was missing.
|" greatest breadth||3·5||3·5||3·4||3·5||3·6||4·0|
|Anterior palatinal foramina||5·5||6·5||5·7||5·7||6·4||5·7|
|Condyle to incisor-tip||21·5||22·5||22·5||23·0||24·4||23·0?|
|Coronoid-tip to angle||9·5||10·0||9·5||9·8||10·0||9·2|
During the first week in January, 1908, few rats were seen, but their numbers increased gradually, until in March and April they were plentiful.
In June rats were very numerous about our camp in Denham Bay, being seen frequently in the daytime, but more especially in the evenings, when they invaded our whares.* They searched everywhere for food, but did not gnaw into any of our boxes. Although naturally timid, they would explore every part of the whare if we kept quite still, and, as soon as the light was out, jump up on the table near which two of our party slept, and would sometimes even run over us as we lay in our bunks. We poisoned them periodically with arsenic, but it merely checked their numbers for a few days, after which they appeared as numerous as ever.
As showing the large number of rats that exist on Sunday Island, the following figures are given on the authority of Mr. R. S. Bell. He estimated that in three years 44,000 were killed by poisoning and other means, while on one occasion 173 were caught in a single night near the cultivations in Denham Bay by means of a trap made with a harbour-buoy.
The rats decreased in numbers during July. In August, on wet evenings but few were to be seen, but on fine nights a fair number came about our whares. During September and October very few were noticed.
That the rats disappear into the ground during the summer months seems certain, for on one occasion Mr. R. S. Bell accidentally dug out one of their burrows and discovered a number of rats which appeared somewhat sleepy and dazed on being turned out into the daylight. During their out-season they usually retire to their holes in the daytime; when surprised in the forest they immediately make for their burrows and disappear. It is probable that they breed in the ground, as young ones were noticed chiefly at the end of summer.
Their food consists principally of fruits. Bananas, oranges, passions, grapes, and figs all disappear before hordes of rats, and the settlers on Sunday Island must protect their fruit-trees if they wish to have any share of the fruit. A piece of tin nailed round the stem at a distance of about 2 ft. from the ground will prevent rats from climbing the tree, but bananas must be cut just as the first signs of yellow begin to appear in the fruit, and placed in some position where rats are unable to get at them.
Sunday Island rats are not strictly frugivorous, but, on the contrary, will eat any kind of food. Birds and their eggs, when they are to be obtained, are eaten, also the flesh and fat of goats, while specimens of rats I had gathered for examination when thrown out were usually devoured by their own kind. The beaches were constantly searched, and any fish or other animals cast up by the sea eaten by rats.
Origin of the Rat in the Kermadecs.
When first discovered by Europeans, Macauley Island was described as having a “great number of rats and mice” (Watts, 1789, p. 228). There is no similar record for Sunday Island, though this island is now overrun with the Pacific rat (Mus exulans), which could scarcely have been introduced by Europeans, who have been the only visitors to the group since its discovery, a little more than a hundred years ago, and who would have introduced,
[Footnote] * Huts made of a framework of poles, with sides and roofs of rushes, palm-leaves, or banana-leaves.
if any, the more widely distributed and powerful grey and black rats. These, however, are unknown in the Kermadecs.
Remarking on Lieutenant Watts's narrative, Mr. Cheeseman says, “This would seem to prove that the species, whatever it may be, is truly indigenous” (Cheeseman, 1888, p. 163). Mr. O. Thomas, in his note on some rats collected on Sunday Island, says that the Pacific rat “has probably travelled from island to island in Native canoes, or on floating logs, &c.” (Thomas, 1896, p. 338). Now, if floating logs carried rats to the Kermadecs in the first instance, then the species would be truly indigenous, provided it had not been introduced through the agency of man to the country whence it migrated to the group.
The Kermadec Islands are, from a biological standpoint, oceanic in character. In order to reach the groups, therefore, rats must cross about six hundred miles (1,000 km.) of ocean, which is the distance to the nearest land. The time which would be taken by a floating tree drifting this distance negatives the possiblity of rats reaching the group in this manner.
The Pacific rat occurs in all the principal groups of islands in the Pacific Ocean. As many of the inhabitants of these islands used it as an article of food, it would often be carried intentionally from one island to another. Probably, however, it was more often carried accidentally in the Native canoes. Being a small, timid, and harmless animal, it would not be troubled much by the Native navigators, and this, possibly, may explain its wide distribution.
On Sunday Island there have been found from time to time stone axes of a similar pattern to those made by Maoris. Other evidence of Native occupation of the group is furnished by the large holes on the Terraces, which, from their position, number, and size, have evidently been made by some Native race. Probably they were chiefly ruas, or storehouses for food. In some of the larger holes, however, were large water-worn stones, no doubt brought from the beach below. These larger holes may be hangis where the Natives prepared their ti-root.
There is no doubt then that the Kermadec Islands were at one time inhabited by Natives, and it is by them, either accidentally or intentionally, that I consider the rat has in all probability been introduced.*
List of Works referring to Sunday Island Rat.
1789. Watts, Lieutenant: Chapter xx of “The Voyage of Governor Phillip to Botany Bay.” London.
1887. Smith, S. P.: “The Kermadec Islands; their Capabilities and Extent,” p. 24. Wellington.
1888. Cheeseman, T. F.: “On the Flora of the Kermadec Islands; with Notes on the Fauna.” Trans. N.Z. Inst., vol. 20, p. 163.
1896. Thomas, O.: Proc. Zool. Soc., 1895, p. 338.
1897. Waite, E. R.: “The Atoll of Funafuti, Ellice Group” (Mammals). Mem. Aust. Mus., 3, p. 165.
[Footnote] * In my paper on the “Vegetation of the Kermadecs” (Trans. N.Z. Inst., vol. 42, p. 173) I have included the candlenut (Aleurites moluccana) and the Polynesian ti (Cordyline terminalis) in the list of introduced plants, as they are not distributed generally in the forest, but are found only in habitable parts of Sunday Island, where they appear to be survivors of the abandoned cultivations of a Native race.