When the chicks are small they are kept completely covered by the parent who sits on the nest. They grow, however, at an enormous rate, gobbling vast quantities of food as it is brought to them, their elastic bellies seeming to have no limit to their capacity ([Fig. 59]); indeed, when standing, they rest on a sort of tripod, formed by the protuberant belly in front and the two feet behind.
I weighed a chick at intervals for some time, and this was the astonishing result:
| Ounces | |
|---|---|
| The egg | 4·56 |
| The chick when hatched | 3·00 |
| Five days old | 13·00 |
| Six days old | 15·75 |
| Eight days old | 24·75 |
| Nine days old | 28·50 |
| Eleven days old | 37·75 |
| Twelve days old | 42·50 |
To see an Adélie chick of a fortnight's growth trying to get itself covered by its mother is a most ludicrous sight. The most it can hope for is to get its head under cover, the rest of its body being exposed to the air; but the downy coat of the chick is close and warm, and suffices in all weathers to protect it from the cold. [Fig. 60] illustrates what I have said very well, whilst [Fig. 61] shows a mother with a chick twelve days old.
Whilst the chicks are small the two parents manage to keep them fed without much difficulty;[(6)] but as one of them has always to remain at the nest to keep the chicks warm, guard them from skuas and hooligan cocks, and prevent them from straying, only one is free to go for food. Later on, however, two other factors introduce themselves. The first of these is that the chick's downy coats become thick enough to protect them from cold without the warmth of the parent; and the second that as the chicks grow they require an ever-increasing quantity of food, and at the age of about a fortnight this demand becomes too great for one bird to cope with. At this time it is still necessary to prevent the chicks from straying and to protect them from the skuas and “hooligans,” and so to meet these two demands a most interesting social system is developed. The individual care of the chicks by their parents is abandoned, and in place of this, colonies start to “pool” their offspring, which are herded together into clumps or “crèches,” each of which is guarded by a few old birds, the rest being free to go and forage.
Fig. 60. A TASK BECOMING IMPOSSIBLE
It is quite likely that if a chick which has escaped from its own crèche joins another crèche it will get fed there, as it seems hardly possible for the adults to recognize the individuals of so large a gathering and to detect a stranger should one turn up, but there is good reason to believe that the old birds work for their own crèches only, and remain faithful to them for the rest of the season, because, as they make their way across the rookery, laden with the food they are bringing from the sea, it is sadly common to see them pursued by strayed and starving youngsters, plaintively piping their prayers for a meal; and these appeals are always made in vain, the old birds turning a deaf ear to the youngsters, who at last, weary and weak, give up the pursuit, and in the end fall a prey to the ever-watchful skuas. Further evidence is found in the fact that the chicks at the very back of the rookery and up at the top of the Cape are just as well nourished as those nearer the water, who are constantly passed by a stream of food-laden parents.