“The cuckoo is at least as large as a turtle-dove,” their uncle continued. “Its plumage is ashy gray on the back and white underneath, with numerous brown crosswise stripes resembling those seen on many birds of prey. The wings are long, as is also the tail, which is spotted and tipped with white. Despite its likeness to the goshawk and sparrow-hawk, the cuckoo is not to be classed as a bird of prey. Its talons lack the necessary strength, and its beak, which is rather long, is flattened and only slightly curved. Those are neither the hooked claws nor the savage beak of a bird living the life of a murderer. The cuckoo’s food consists entirely of insects and caterpillars. You remember the processionaries of the oak tree, those frightful black caterpillars that spin large silken nests against the trunk of a tree and bristle with barbed hairs that cause such terrible itching if you touch them?”
“Yes,” answered Jules; “and you told us that the cuckoo eats those caterpillars.”
“It feasts on them, as it does on all hairy caterpillars; but the hairs are rolled up into a ball in the stomach and thrown up through the beak. As a greedy devourer of insects and caterpillars the cuckoo deserves protection; the only regret is that a multitude of little birds most useful to us should be destroyed by it. Let us consider the facts of the case.
“The female cuckoo never builds a nest, nor does [[191]]she know how to hatch out her own young; but let us plead the best excuse we can for her. Her breast seems to be so formed as not to impart enough warmth to eggs to make them hatch; and, more than that, she lays so often throughout the summer as to leave her no time for making a home of her own. In short, this bird never knows the joy of taking care of her young. It is not because she will not hatch her own eggs, but because she cannot. She has to leave this work to other birds.”
“Then the cuckoo’s egg I found in the garden nest was left there for the warbler to take care of?” Jules inquired.
“Precisely. Now see by what wonderful planning the strange egg comes to be adopted by another mother. Bear in mind that the cuckoo lives exclusively on insects. The young cuckoo must have caterpillars. Where will food of this sort be found if not in the nests of birds that feed on insects, as for instance warblers, redbreasts, tomtits, nightingales, stonechats, wagtails, and others? It is to just these nests that the cuckoo goes. Sometimes it may chance to lay its eggs in the nests of birds that live on seeds, such as linnets, bullfinches, greenfinches, or yellow-hammers; but even then the choice is wise; for if the foster-parents are eaters of seeds they bring up their young on worms, which are easier to digest, and so the little cuckoo finds in these nests food suited to its needs. But the cuckoo’s eggs are never laid in the nests of quails, partridges, or other species whose young are granivorous [[192]]from the beginning. In a brood whose habitual diet was not theirs the changelings would surely die of hunger.”
“But how,” asked Jules, “does the cuckoo know what nests to choose and what ones not to choose, when it lays its eggs?”
“If it knew why it laid its eggs where it does, I should have to admit that the cuckoo’s sagacity surpassed man’s; but it does not know at all the reason for its choice. A wise Providence has arranged everything for the bird. The egg—which, judged by the cuckoo’s size, should be as large as a pigeon’s or a turtle-dove’s—is hardly as big as a sparrow’s, so that it can easily find a place in the warbler’s or even the wren’s tiny nest without arousing the adoptive mother’s suspicions. Moreover, this egg is variable in its color, as if the better to harmonize with the coloring of those with which it will be incubated, whether in this or that or the other nest. Sometimes the cuckoo’s egg is ash-colored, at other times red, green, or pale blue. It may closely resemble the sparrow’s eggs, or it may be mottled with spots of smaller or larger size, in lesser or greater numbers; or, again, it may be marbled with black streaks. But, despite these variations, it is always easy to see the difference between the cuckoo’s egg and the others in a nest. If one of the eggs is found to differ from the others in shape and color, that one certainly came from the cuckoo. By that sign alone I recognized the egg we have here from the warbler’s nest.” [[193]]
“The other five,” Jules declared, “are as like one another as so many drops of water; but the sixth, which you have there, is very different.”
“And that is why I am sure it belongs to the cuckoo,” replied his uncle.