Cuckoos do not raise their own young. They are said to be brood parasites. They lay a single egg in a nest that already contains several eggs while the parent bird is away. Although cuckoo eggs are often slightly bigger than the other eggs, the female cuckoo has the extraordinary ability partially to match the colour of her egg to the others. The eggs are hatched by the host bird. The young cuckoo is bigger and stronger than the other nestlings and demands more food. To ensure that it receives all the food brought to the nest by the foster parents, it pushes the other young birds out of the nest.
When she’s ready to lay an egg, a female cuckoo canorus swoops to the unattended nest of a smaller species. She then swallows one of the eggs that have been laid there and lays one of her own—a behavior known as brood parasitism.
Sometimes potential victims revolt. The parents that inhabit the nest may mob the cuckoo mom, preventing her from dropping off her egg; they may push out cuckoo eggs before they hatch, or they may even abandon the nest.
But often the cuckoo mom gets away undetected, leaving her parental duties behind, and the nest’s owners return none the wiser. C. canorus is known to have passed its eggs on to more than 100 host species, according to the International Union for Conservation of Nature.
When the cuckoo chick hatches, it ejects other eggs or hatchlings to get all the space—and food—for itself. Hungry as a whole brood, the outsize baby devours everything brought by its foster parents—in the photo above, the provider is a reed warbler, a common host.
Franka Slothouber, a retired photo editor who’s an avid wildlife photographer, observed the birds’ behavior in 2014 in Amsterdam, where she lives. “The poor warbler almost disappears in the wide-opened mouth of its ‘adopted’ baby,” Slothouber says. And yet “the warbler couple is convinced this chick is theirs and treats it accordingly, by feeding it until it can look after itself.”
Picture Credit : Google