The cuckoo dresses like a hawk so it can sneak its eggs into nests
A female cuckoo may visit as many as 50 nests in a season, leaving eggs for other birds to raise. To get close, she looks like a predator: grey back and barred belly, much like a sparrowhawk. When researchers covered those stripes on stuffed cuckoos, reed warblers attacked them more fiercely.
The common cuckoo is an obligate brood parasite, which means it never raises its own young. More than 100 host species have been recorded, with meadow pipits, dunnocks and reed warblers the favourites in northern Europe. Females fall into lineages called gentes, each specialising in one host and laying eggs that match that host's colour and pattern, even though cuckoo eggs are bigger. Once hatched, the cuckoo chick shoves the host's eggs out of the nest.
Hosts fight back by learning. Warblers mob cuckoos more after watching their neighbours do it, and they learn to target whichever plumage they saw mobbed. That may explain why some females come in a reddish-brown form as well as grey: whichever version is rarer escapes the learned hostility and does better, keeping both forms in circulation.
The name imitates the male's two-note call, and the English word, from Old French, turns up around 1240 in the song Sumer Is Icumen In, whose opening urges the cuckoo to sing loudly because summer has arrived. The call starts in April as a falling minor third and stretches through a major third to a fourth as weeks pass, until by June the bird seems to lose its tune altogether. Carl Linnaeus described the species in 1758, and its Latin name canorus means melodious.
Cuckoos arrive in Europe in April, leave in September and winter in Africa. They are fond of hairy caterpillars that most birds find distasteful. Estimates put the world population at 25 to 100 million birds, but numbers are falling, and in Britain between 1995 and 2015 they declined by 69 percent in England while rising by 33 percent in Scotland. The oldest known British cuckoo lived almost seven years.
Source: Common cuckoo
