Page:The British Warblers A History with Problems of Their Lives - 5 of 9.djvu/67

 the nest for short periods, generally returning with her bill full of insects. About the fourth day the brooding becomes considerably less, and in proportion the supply of food increases, until both sexes are often at work together collecting and bringing supplies. The fæces, enclosed in a membraneous sac, are ejected by the young after the food is delivered to them, and are then carried away or eaten by one or other of the parents. If defæcation does not immediately take place the parent touches the youngster's anus with its beak, which usually has the desired effect.

As it is possible to obtain so clear a view of the nest and of the behaviour of the parents, I have been much interested in noticing the method adopted by them when actually delivering food to their offspring. Where there are four or five young in a nest we should expect to find the food delivered more or less in rotation. But this does not seem to be the case. In fact it may happen that both parents arrive at the nest simultaneously with food in their bills, and deliver it into the gape of the same young one, and also that the same bird is fed over and over again until—and this will scarcely be credited—it lies with bill open, apparently too exhausted to swallow so large an amount of food. At other times the insects are divided more evenly, three of the young perhaps receiving food from one parent; and part of it may be even withdrawn from one gape and placed in another.

The young do not all develop with equal rapidity. The growth can easily be watched day by day, and it will be found that the feathers are more developed on one bird than on another, and ultimately that one is ready to leave the nest before the others, and moreover does actually do so, a difference perhaps of one day, or in some cases even of two days, intervening. By the expression "leaving the nest" I do not necessarily mean deserting it, but that the bird is sufficiently developed to make short excursions amongst the reeds, returning again to the nursery; nevertheless, cases have come