Cuckoo Finch (Anomalospiza imberbis), a sub-Saharan African species, has adopted a unique disguise to help it lay eggs in other birds' nests, biologists have found.
The study, published in the journal Proceedings of the Royal Society B, shows that female Zambian Cuckoo Finches have evolved be nigh-on indistinguishable from female Euplectes weavers, such as the harmless, abundant and sympatric Southern Red Bishop (Euplectes orix).
Dr William Feeney, from The Australian National University (ANU), told Science Daily: "The Cuckoo Finch is so similar to the innocent bishops, that the target of the trickery, the Tawny-flanked Prinia, cannot tell them apart. The Cuckoo Finch looks a lot more similar to the bishop than its nearest relatives, the Vidua finches, suggesting that it has evolved to be able to hang around prinia nests without arousing suspicion."
Like cuckoos, the iconic family from which the species gets its name, Cuckoo Finches are brood parasites who lay their eggs in the nests of other birds, to deceive them into raising the parasitic young as their own.
Brood parasites use a range of methods to deceive their hosts. Mimicry of a harmless model (known as aggressive mimicry) is used by egg, chick and fledgling brood parasites that resemble the host's own eggs, chicks and fledglings. However, Dr Feeney's research is the first to find that an adult brood parasite has evolved to look harmless in an attempt to fool their host.
Dr Feeney added: "This shows that brood parasites use this kind of wolf-in-sheep's-clothing disguise in all stages of their life cycle: as eggs, chicks, fledglings, and we now know, as adults."
However, the prinia hosts are wising up to the attempted deception. Professor Naomi Langmore, Dr Feeney's PhD supervisor at the ANU Research School of Biology, explained: "The prinias have learned to react aggressively towards the innocent female bishops, which look like female Cuckoo Finches. They reject foreign eggs from their nest at a higher rate after they have seen either a female Cuckoo Finch or a female bishop. But they do not act the same way if they have seen males of either species, which look quite different."