Why cuckoo throw eggs?
Most birds build nests, surround the laying of eggs and take care of the offspring themselves. But there are exceptions. The most famous – cuckoo. Although not all of them are nesting parasites. In the family of cuckoo 140 species, and only 50 of them throw eggs.
Mostly cuckoo, shifting care of his offspring on other birds, live in an eastern hemisphere, and responsible parents – in Western. Especially a lot of non-parazitic species in North and South America. For example, Cuckoo Ani and Guira most often withdrawing offspring. For rare exceptions, the nests themselves and the chicks are sitting in chicks.
Five types of cuckoo are found in Russia, among which the most common cuckoo is ordinary. It is she – one of the most famous nesting parasites.
Mostly cuckoo, shifting care of his offspring on other birds, live in an eastern hemisphere, and responsible parents – in Western
For an ordinary cuckoo, "polygamy" is characterized, that is, the marriage portion of the male includes several females, which he visits. At the same time, the male guards it so that in one nest there were no eggs of other cucks. And the female during the reproduction period is trying to find exactly the type of birds whose representatives at one time focused her. It is focused not only on the appearance, but also to the voice. Basically, it is a sparrows nests. All because a growing cuckoo is required for the proceedings a lot of insects, namely, the sparrows will feed their chicks, without tired of working in the morning until the evening.
For the season, the cuckoo postpones more than ten eggs, and many researchers believe that they are simply not able to feed them on their own, and then it is simply not able to feed each chick. That is why she shifts the care of them on other feathered.
Cuckoo tries her eggs to throw into another unfinished masonry. And since the embryonic development of their chicks are short – only about 12 days, it allows them to hatch earlier neighbors in the nest. Then the cuckoo begins to methodically throw out all the eggs or even hatched chicks. To do this, the blind and seemingly helpless chick have a special mechanism: there is a sensitive zone on a bare back, when touched by a discharge instinct. A similar scenario is implemented by nature because the cuckoo will grow much more receiving parents, therefore, he needs all the food we bring. On the 20th day he will leave the nest, heating the last two, and then three times.
But the cuckoo is not one of a kind. The phenomenon of nesting parasitism is often found among waterfowl birds. Among the ducks they are famous for Peganki (Ogari), which throw their eggs in the nests of neighbors – other Peganok. The eggs of the long-axis crochal come across the nests of the black turpana, and the white-eyed squils sometimes postponing his ducks of the Savok. Nest parasitism meets even in a white goose!
True, these birds have such a tendency is not fixed by natural selection. The reason is simple: other people’s chicks are most often dying. First, the female fails to cover all the eggs with their body. Secondly, "acceptances" do not find a common language with someone else’s mother, as a result, beaten from brood and die from predators. Therefore, usually ducks throw eggs only to unfavorable conditions for the nesting period. Probably when they feel that they will not be able to feed offspring themselves.