THE CUCKOO.
We have two species of cuckoo in the United States, but each of them builds a nest of its own, and rears its own young, although our yellow-billed cuckoo is a very bad nest-builder, and is said often to desert its young, leaving them to starve unless other birds take pity upon them and bring them food. Most of our smaller birds are very sympathetic during the breeding season, and are ready to give food and care to any young bird which needs it, even if it is not one of their own species.
Although our American cuckoos have not, as a general thing, the bad habits of those of Europe, we have another very common bird which is hatched and brought up by strangers. Every boy who lives in the country knows the cow-bird, cow-blackbird, or cow-bunting, for it is called by all these names. It is a small bird, a little larger than the bobolink and of much the same shape. The male has a dark-brown head and a bright greenish-black back and wings, but the female is so much lighter in color that you would hardly believe that they belong to the same species. These birds are very abundant in the spring and summer, and may be seen in flocks flying and feeding in company with the red-winged blackbirds. They are often found among the cattle and sheep in the pastures and barn-yards, and they derive all of their common names from this habit. Although nearly related to the orioles, which make such wonderful nests, the cow-birds make none at all, but lay their eggs in the nests of other birds, such as the blue-bird, chipping-bird, song-sparrow, yellow-bird, and some thrushes and fly-catchers. Like the cuckoo, this bird usually chooses the nest of a bird much smaller than itself, but as its egg is not small, the deception is at once discovered, and the birds whose nest has been selected for this purpose are very much disturbed. It is necessary for the female cow-bird to find a nest in which the owners have just begun laying, for if the owners have no eggs of their own they will desert the nest, and if their own eggs are somewhat advanced before the cow-bird's egg is laid, their own young will hatch first, and the parents will then leave the nest to hunt for food, thus allowing the cow-bird's egg to become cold and die.
When the female cow-bird is ready to lay her egg, she often has great trouble in discovering a nest at just the right stage. She leaves the flock and perches upon some tree or bush, where she can have a good view of all that is going on. When she discovers a nest by watching the actions of its owners, she waits for an opportunity when both the owners are away, when she approaches it very stealthily, but quickly, keeping a very sharp watch, to be sure that she is not observed. If she finds that the nest is fit for her purpose,—that is, if the birds have laid only a part of their regular number of eggs,—she drops one of her own eggs into it, and then disappears as swiftly and quietly as she came. If she is unable to find a suitable nest in her own vicinity, she goes in search of one, examining every thicket and bush—sometimes for a long distance—until she finds one. A gentleman once followed a cow-bird along the shore of a stream for two miles before she succeeded in finding a nest which satisfied her. Occasionally, two or more cow-birds' eggs are found in the same nest. It is not known whether both of these are laid by the same bird, but it is more probable that in such a case as this two cow-birds have visited the same nest.
The egg of the cow-bird has one interesting and important peculiarity. It is necessary, as we have seen, that this should be hatched before the other eggs; for if it were not, the old birds would stop sitting and allow it to become cold as soon as their own young were hatched. This danger, however, has been provided against, since the egg of the cow-bird needs only eight or nine days of incubation, while the eggs of those birds in whose nests it is usually found require from twelve to fifteen days. A short time after the young cow-bird is hatched, all the other eggs disappear, and they may sometimes be found on the ground, broken, at a considerable distance from the nest,—so far away that the young cow-bird could not possibly have thrown them there. The way in which they are removed from the nest is not known, as no one has yet watched closely enough to say whether the parents themselves destroy them, or whether the female cow-bird returns to the nest and removes them, to give more room for her own young when hatched.
I have already said that the smaller birds are very much disturbed and troubled when they find one of these eggs in their nest, and are very apt to desert it and go to another place if they have not yet any eggs of their own. Our common yellow-bird, however, is sometimes wise enough to find a better way out of its trouble. It values its neatly finished nest too highly to desert it, and it is not strong enough to lift the big egg and throw it over the edge, so it gathers a new supply of hay and hair, and makes a false bottom to cover up the egg. Then it makes a new lining to the nest, and lays its own eggs upon that, so that the cow-bird's egg does not receive any of the warmth from its body, and never hatches.
EGG OF COW-BIRD.
I have given you several reasons for believing that birds are able to think for themselves; but I do not see how anything could prove this more clearly than this expedient of the yellow-bird for saving its young from destruction by preventing the hatching of the cow-bird's egg.