Revealed: how cuckoo finches crowd the nest

The African cuckoo finch is known for bamboozling other birds into raising its young, but new research has shown just how brazen the feathery rogue is in evading parental duty. The yellow, streaked bird, about the size of a sparrow, is a notorious freeloader. It lays its eggs in the nests of other birds, and even tries to match its egg colouring to those of its hosts. It does this to gull the birds into becoming unwitting foster parents: hatching the cuckoo finch eggs along with their own, and then raising the chicks when they emerge from the shell. Now scientists have witnessed for the first time just how persistent the cuckoo finch can be in its grand scheme of deception. The female returns to the same host nest several times to lay as many eggs as possible, probably at a rate of about one egg every other day, according to a study in the journal Nature Communications. By laying several eggs in the same nest, the cuckoo finch confuses the hosts, making them less likely to spot and eject the intruder eggs among their own. "The cuckoo finch has evolved a novel strategy... to defeat host defences and increase its reproductive success," said study co-author Martin Stevens from the University of Exeter. "They can outwit the hosts and help more of their young to be reared." The cuckoo finch chicks often grow faster and beg more loudly for food than the host chicks -- which die of starvation as the intruders are given more food by their cuckolded parents. In Zambia, where the study was done by a team from Britain and South Africa, the cuckoo finch's most frequent victim is the African tawny-flanked prinia -- a bird of similar size but duller in colour. The cuckoo finch is in the family of indigobirds and whydahs. It is distantly related to the "true" cuckoo, which migrates between Africa and Europe. The prinia usually lays clutches of two to four eggs and breeds during the wet season, about February and March, in Zambia. About a fifth of prinia nests are invaded by cuckoo finches, but hosts sometimes discover the intruder eggs and kick them out, said Stevens.