Now follows in narrative form a progressive description of the various features and behaviour of the chick during its life in the burrow. In conclusion, a short account is given concerning mortality and a strange inertia which overcame several chicks.
As already stated, the earliest chicks usually begin to hatch during the fourth week of December. Weighing about 9 grams, they are covered with relatively very long down, which is 25 mm. in length, and a light neutral grey (31 σ *), in colour. In fact the down tones exactly with the secondary down of the Titi Wainui chicks.
The down of the head, covering entirely the eyes and beak, is 15 mm. long, and as the feet are also hidden in down the chick looks like a fluffy powder puff. Its squeak is faint, resembling that of the Titi Wainui chick. On top of the head is a bald patch, at first a bright flesh colour, which is entirely hidden by the down. This characteristic was noted in the British Storm Petrel by Lockley (1932, p. 210). Regarding Leach's Petrel, Ainslee and Atkinson (1937, p. 239) state that there is no bald patch. Gross (1935) doe not mention the feature at all, while Roberts (1940, p. 173) says it is also absent in Wilson's Petrel.
Owing to the presence of the very long down it is difficult to tell whether or not the chick is hatched bright-eyed. I am inclined to think that it is, for one day, a chick, on the day after it was hatched, had its eyes half open. Most of them, however, have the lids closed when inspected, but this is probably due to exposure to strong light. I have one record of eyes being closed when examined for eight consecutive days after hatching.
When first hatched the chicks appear to be very lifeless, lying inertly, frequently on one side. After a day or two they will, if touched, jump round quickly as though they had received an electric shock. At this stage, too, some of them will bite the finger.
Considerable growth is manifest by the beginning of the second week, in spite of the chick having been left alone almost immediately after hatching, and consequently experiencing irregular meals. Its movements have become much quicker and although its eyes are still closed when removed from the burrow it will open them for a peer round. The down of the back is now 30 mm. long, while the bald patch has changed almost to the colour of the down, with vestiges of what appear to be down of a very light neutral grey in colour (31s). There is no evidence whatsoever of secondary down on the body. In fact, it was soon discovered that the Storm Petrel chick does not develop two downs as is the case with penguins and with other petrels which I have studied. In proportion, however, the down is much longer than in these last-mentioned species.
The single down has also been commented on by Roberts (1940, p. 174), who noted the characteristic in a series of Wilson's Petrels. It is interesting to note, too, that his birds had wing quills from 1 to 3 mm. long when 11 to 12 days old. In Table V below I have recorded that the hand quills of Pelagodroma appear on the twelfth day, thus
[Footnote] * The key to this and other colour numbers is given at the end of the last part of this paper. The numbers are those used in Radde's colour chart.
corresponding with Wilson's Petrel. Lockley (1932, p. 210), however, states that the British Storm Petrel has a thick double-down.
After a preliminary study of the appearance of the feathers in 1940-41, I watched the phenomenon with greater care in the following year. Seven chicks were closely watched and the results given in the table below were obtained. This table also serves as a useful age chart for chicks which have been found after they have hatched.
|Feature.||First Appearance of Feathers.|
|White forehead.||38th day.|
|Disappearance of egg tooth.||Average, 15th day.|
|Range, 11th to 20th day.|
No doubt other observers might arrive at different results from what I have given in the above table on account of the difficulty in seeing and deciding when the feathers appear. It would be quite easy not to notice their appearance for some days.
At the beginning of the third week the feathers all over the body have attained a length of 5 mm., while the feathers on the scapulars, forearm, and hand may be easily detected. The bald patch, sparsely covered with short tufts of feathers, has now become darker than the down. A decided change has overtaken the webs of the feet, the colour having turned from bright pink (29q) at hatching, to a faint bluish colour (21u). The head no longer lies on the side, while the chick is able to hold its beak off the ground with ease, and it is also beginning to spring along the ground off its tarsi. That the egg tooth also disappears at this stage was arrived at by testing out 14 chicks during two seasons, when the tooth was found to disappear between the 11th and 20th day, becoming worn to such an extent that it dropped off. The average time is the 15th day. Up to the 16th day there were 11 cases, one on the 18th and two on the 20th day.
By the fourth week the down is very loose, as it is being pushed out by the rapidly growing feathers. The tail is through on the 21st day. The belly of the chick, being very rotund, fits comfortably into a little hole in the nest. Though the bald patch is better covered, the feathers are still in tufts. When touched the chick bites quite freely, while if it has been handled since hatching it is very playful, tugging and pulling at anything on the observer within its reach. Every time it moves, the eye is now fully open, though still hidden by the long, shaggy down. The bill has now assumed all one dark colour, the lighter patches having all disappeared.
By the 29th day the down is extremely loose on the breast, where the white feathers are plainly visible. The top parts of the bird are better hidden while the tips of the primaries are just showing through the down. The position of the bald patch though well covered can
still be seen. Later on in this week the tips of the tail appear through the down. The chick, of course, has increased in liveliness and playfulness.
On the 36th day the wings are practically free of down and the juvenal characteristic of light edgings on the primaries and some of the secondaries is very pronounced. The rest of the back and head, except the now covered bald patch, still retains considerable down. On the 38th day a good age characteristic develops when the bare area at the forehead and over the gape becomes studded with little white tufts of feathers. This area grows rapidly. On the 40th day a faint narrow line of white appears over the top of the eye.
At the beginning of the seventh week the chick can walk about freely either flat on its tarsi or in the half raised position. The scapulars, secondaries, and primaries looking very beautiful with their white edgings, are now fully exposed. The down on the back is very thin, while there is round the position of the bald patch still a thick ring of down, which continues to obscure the eyes. During this week the white forehead and eye stripe areas thicken up into a white mass, forming another juvenal characteristic. In the adult these areas, especially that of the forehead, contain more dark feathers.
By the beginning of the eighth week there are only a few strands of down on the back, with a bigger patch over the tail and round the vent. Circling the head is a thin crown through which can be seen the outline of the head. There is a patch under the neck and a thin collar round the top.
On the 58th day the particular chick under observation lost the last vestige of down and departed the following day. Most of the webs between the toes of the chicks were dark in colour, in great contrast to the yellow patches seen on the adults. There were, however, odd chicks which showed almost as much yellow as in the adults.
At this stage a word or two about chick mortality would not be out of place. The season 1940-41, which was a good dry one, did not seem to have a high mortality rate. Two of the 18 chicks under observation died, but the cause of the deaths was difficult to define. To my knowledge, no parent was lost during my six weeks' observation.
Several of the chicks became quite wet in the burrows after rain, but most of them seemed to recover again. No. 51 chick was very wet on January 10, but next day it was quite dry and had an adult with it during the day. As this attendance by a parent on the chick's seventh day is unusual, the occurrence may have been due to the condition of the chick.
During February, 1942, five chicks were overcome by a strange inertia. The symptoms I noticed as I took them from the burrow were that the eyes were shut, the wings stiff, half open and quivering violently, while at the same time the chick was cold. After being put in a sock and kept warm they soon recovered. I can offer no explanation for this phenomenon. One chick, which was my favourite, because it had become extremely tame and playfully aggressive, was one of the victims. On February 10 it had not been fed and was in normal health. On February 11 and 12 it was still unfed but suffered a bout of inertia each day. The two succeeding nights it received.
7 ½ and 18 ½ grams of food, and was not ill again. A second chick was found to be inert on February 7 and had received 8 grams of food. During the next two nights it was given ½ and 18 grams respectively, and then remained unfed on February 10. No food was given the following day, when the chick was again inert. On February 12 it had received the enormous meal of 25 grams, and was not ill again. I have no weight records of the other three chicks.
In 1941-42, of the 52 chicks hatched in burrows under observation, 47 of these ultimately left the island. Concerning the five that died, one was scraped out of the nest by Titi Wainuis, while the other four were found to have disappeared during a period of some weeks when I was not examining the nests. Only the first chick was lost among the nests I was examining daily. The 1941-42 season was also a good dry one.