Cuckoos Impersonate Raptors with Matching 'Outfits'

The cuckoo, a tricky bird known for invading the nests of other birds to lay parasitic eggs, may have another trick up its sleeve: researchers have documented the cuckoo's plumage to be remarkably similar to that of birds living in the same region, which they contend the birds use as another weapon in its arsenal of trickery.

Writing in the journal Animal Behavior, a team of ornithologists contend that the cuckoos striped feathers resemble local birds of prey such as sparrowhawks, which they may use as a form of offensive camouflage.

A cuckoo that appears to be a sparrowhawk approaching a nest at high speed could be enough to scare away a bird resting in it, leaving the cuckoo wide open to lay its parasitic eggs, which tend to blend in nicely with those of the host bird.

While the the similarities in the two birds' plumage has been studied previously, the latest reseach contends that the cuckoo's attempt to physically impersonate another animal -- something called Batesian mimicry -- may be more widespread in cuckoos than it is in other animals.

Furthermore, the species of bird the cuckoo resembles tends to match the species of raptor common to the cuckoo's neighborhood.

"There is no benefit in looking like a dangerous species your target is not familiar with," said lead researcher Thanh-Lan Gluckman from the University of Cambridge's Department of Zoology.

"We first established similarity in plumage pattern attributes between cuckoos and raptor species, and then showed that cuckoos look nothing like species from a different geographical area."

The cuckoo's Batesian mimicry allows them to fly about uncontested, spotting potential places to lay their parasitic eggs.

"The barring on their plumage helps cuckoos conceal themselves while searching for potential nests, then when they approach, the host of the nest may mistake a cuckoo for a raptor coming to get them -- giving them unfettered access to lay eggs," Gluckman said.

Gluckman and his colleagues contend that this form of mimicry may be widespread among different cuckoo species and that they may be mimicking different birds of prey. Studying cuckoos living in different areas with a digital imaging analysis, the researchers found no matching patterns between cuckoos and raptors living in different regions.

"These findings underscore the importance of using digital image analysis to objectively quantify plumage patterning in mimicry -- it is important not to make assumptions about even simple patterns such as these," added Gluckman.

"We hope this encourages other researchers to examine the function of barred plumage in parasitic cuckoos and raptors the world over."