Revealed: The con trick cuckoos use to scare off rivals

Scientists have discovered how clever mimicry persuades other varieties to vacate their nests accept their eggs

They are notorious for their feckless parenting skills, leaving their offspring to be cared for by others. Now, it seems, cuckoos have other socially reprehensible characteristics: they are fraudsters. Zoologists from Cambridge University have shown how the cuckoo's plumage allows the bird to pass itself off as a hunting bird of prey such as a sparrowhawk. By mimicking local predators, cuckoos are able to scare off birds from their nests, allowing them to replace any eggs with their own.

Thanh-Lan Gluckman and Nicholas I Mundy, both zoologists, have studied the striped or "barred" feathers across cuckoo breasts and discovered that other birds mistake them for hunting birds of prey. Using computer software and digital cameras, the Cambridge team also discovered that the plumage patterns of cuckoos change from place to place to enable them to look like the most threatening predator. A cuckoo in an area with a harrier-hawk population will mimic that species.

"There is no benefit in looking like a dangerous species your target is not familiar with," said Ms Gluckman. "Batesian mimicry", copying the pattern of a more dangerous species, is also seen in other creatures such as hoverflies striped like wasps.

Similar technology helped two other Cambridge University academics, Claire Spottiswoode and Martin Stevens, investigate how African cuckoo finches (unrelated to cuckoos) fool prinia birds into accepting their eggs once they have been sneaked into their nests. Their study in Zambia found that the two species are locked in "an evolutionary arms race" which has seen prinias get better at spotting "imposter" eggs as finches get better at mimicking theirs. The scientists believe that as prinias become better at recognising finch eggs, only those that are the closest match to their own survive to hatching. This natural selection means that the finches who lay eggs most similar to the prinias are those most likely to enjoy offspring.