Page:Popular Science Monthly Volume 76.djvu/548

544 eaten than in others, and there can be no doubt that habit often decides the question. Fear, however, is another variable to be reckoned with, for if this sense is aroused at the moment the bird has seized a sac to bear it from the nest, it seems to be eaten as the easiest solution of the difficulty. Perhaps a counterpart of this sort of behavior is seen when a bird with food in bill suddenly encounters the naturalist, or any other fearsome object, for it immediately sounds the alarm, and promptly swallows the insect. When more than one sac is taken, all are usually eaten. It is not an uncommon sight to see a bird walk around the nest and take a "white marble" from three birds in succession, for in muting, a bird is sometimes followed by one or more of its mates, and anything which soils the nest is quickly removed. More than once I have seen a sac, which had dropped from a nestling snapped up by the old bird before it had fallen two feet in the air; and birds will even descend to the ground for the sacs, if necessary. Twice I have seen the male chestnut-sided warbler take a sac to carry it off, and the hungry female snatch it from him, devour it and settle down to brood.

Removing the excreta piecemeal and dropping them at a safe distance is the common instinctive method not only of ensuring the sanitary condition of the nest itself, but, what is even more important, of keeping the grass and leaves below free from any sign which might betray them to an enemy. Bluebirds and redwing blackbirds often carry the sacs a long distance before letting them fall. Crow blackbirds sometimes drop them in the water, and house wrens and nuthatches implant them on the bark of trees. This instinct, like so many others in the reproductive cycle, after running its course, begins to wane, and even before the close of nest-life, so that it is not correct to say that the nest of the cuckoo or the nicker is always sweet and clean. I examined a hoopoe's nest in upper Egypt, near Luxor, on March 26, which was filthy in the extreme, but hardly worse from a sanitary standpoint than is a woodpecker's hole at a corresponding period. This nest of the hoopoe was on the ground in the midst of a pile of sun-dried brick, and was composed wholly of weeds and lentil-pods. The five young ones, which were at this time nearly ready for flight, showed their fear by erecting their beautiful crests and crawling down among the bricks to hide. There is the further curious anomaly regarding this practise, that some of our most attractive birds, which have delicate and artistic nests, of which I can mention the American goldfinch, do not appear to possess the cleaning instinct at all, or the attendant instinct of inspection, and shortly after the young emerge their surroundings become encrusted with filth. This singular fact is, I believe, correlated with the method of feeding described above. The young are fed at rather long intervals; at one period, of nearly seven hours, the average was once every twenty-five and one half minutes, and all are rapidly,