Biological arms races in birds result in sophisticated defenses against cuckoos

New research reveals how biological arms races between cuckoos and host birds can escalate into a competition between the host evolving new, unique egg patterns (or ‘signatures’) and the parasite new forgeries.

Brood parasitic birds such as cuckoos lay eggs that mimic those of their hosts in an effort to trick them into accepting the alien egg and raising the cuckoo chick as one of their own.

New research from the University of Cambridge has found that different bird species parasitised by the African cuckoo finch have evolved different advanced strategies to fight back.

One strategy is for every host female to lay a different type of egg, with egg colour and pattern varying greatly among nests. These egg ‘signatures’ make it harder for the cuckoo finch to lay accurate forgeries. Since the female cuckoo finch always lays the same type of egg throughout her lifetime, she cannot change the look of her egg to match those of different host individuals – thus her chances of laying a matching egg are exasperatingly small.

Dr Claire Spottiswoode, a Royal Society Dorothy Hodgkin Research Fellow from the University of Cambridge’s Department of Zoology, said: “As the cuckoo finch has become more proficient at tricking its hosts with better mimicry, hosts have evolved more and more sophisticated ways to fight back. Our field experiments in Zambia show that this biological arms race has escalated in strikingly different ways in different species. Some host species – such as the tawny-flanked prinia – have evolved defences by shifting their own egg appearance away from that of their parasite. And we see evidence of this in the evolution of an amazing diversity of prinia egg colours and patterns.

“These variations seem to act like the complicated markings on a banknote: complex colours and patterns act to make host eggs more difficult to forge by the parasite, just as watermarks act to make banknotes more difficult to forge by counterfeiters.”

The researchers also found that some cuckoo finch hosts use an alternative strategy: red-faced cisticolas lay only moderately variable eggs but are instead extremely discriminating in deciding whether an egg is their one of their own. Thanks to their excellent discrimination, these hosts can spot even a sophisticated mimic.

via Biological arms races in birds result in sophisticated defenses against cuckoos.

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One Response to Biological arms races in birds result in sophisticated defenses against cuckoos

  1. alfy says:

    It has always been a source of puzzlement to amateur naturalists and also to the professionals, why parasitised bird species cannot see, as we humans do, that the cuckoo chick is clearly an interloper. It is bigger than the normal chicks, noisier and darker in colour, with a bigger and brighter mouth gape.
    It would appear that a strategy of recognition might be the best defence for parasitised species, but for unknown reasons, this “all-round view” does not seem to be open to them.

    It is parallel to the illustration of the robin, a highly territorial bird which will waste energy attacking a bunch of red feathers hung on a stick. It is clearly not a robin or a bird at all, but the poor creature does not seem able to take an “all-round view” of the situation.
    The description of the egg research is a fascinating piece of classical biology among all the molecular work.

    Memo to “deskarati”. The author of the article, Dr Claire Spottiswoode, is a Royal Society Dorothy Hodgkin Research Fellow. Maybe you should post a biog of Dorothy Crowfoot Hodgkin as a suitable subject. Despite the poor lady’s jawbreaking name she was a very distinguished scientist.

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