Fear the Cuckoo—It’s Scarier Than You Think

One of nature's sillier-sounding birds has a nifty way to mimic what it's not

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If you’re a bird and you’re trying to be taken seriously, it can’t be easy to be a cuckoo. In an animal grouping that includes the golden eagle, the sharp-shinned hawk and the great crested heron, being known as a cuckoo does not buy you much cred. Indeed, the only bird that ever had a worse name was the lamentable dodo—and look what happened to him.

But cuckoos are nonetheless fearsome in their own sneaky way. At least three dozen of their many species behave parasitically, meaning that while they produce their own eggs, they often rely on other birds to brood them and care for the chicks. That’s not something the stepmothers do willingly, of course, but parasitic cuckoos in any one region adapt so that their eggs and chicks resemble those of the other bird species that live nearby. All a cuckoo mama has to do is wait until another brooding female briefly leaves her nest, then fly over and drop one more egg among the clutch that’s already there.

The trick, however, is waiting for that opportunity—something that does not come often. Now, a group of researchers at the U.K.’s University of Cambridge have discovered one other, previously unknown bit of cuckoo impersonation: their feather patterns may subtly resemble those of predatory birds, enabling them to scare other females off their nests just long enough for them to pull off their egg-depositing scam.

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Many animal species practice this kind of predator pose—known as Batesian mimicry—and if cuckoos can do it too it ought not to come as a surprise since any similarity between their feather patterns and those of predators should be easily detectable to ornithologists. But bird scientists don’t look at feathers with the same eyes birds themselves do, and that means we see very different things.

“Humans are good at seeing textures,” lead researcher Thanh-Lan Gluckman told TIME. “Birds see in black and white and must interpret texture and patterns in terms of what is known as luminance.” Mostly, this means that the birds have an exceedingly sharp eye for the contrast and intensity of black, white and gray shades and can make distinctions we would overlook. That also helps them recognize subtle variations within a pattern as well as its repeatability and the size of various markings.

In the study, reported in the journal Animal Behaviour, the investigators captured images of various types of predatory cuckoo and ran them through a digital analysis that looked at them in a sort of bird vision—stripping out colors and any other texture and pattern cues humans would use. They then compared the plumage patterns to similarly modified images of raptors, harrier-hawks, sparrowhawks and other predator birds the cuckoos were likely to encounter. Time and again the patterns lined up perfectly—or at least closely enough to convince nesting females that it wasn’t worth waiting around to find out for sure.

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What particularly impressed the investigators was how specialized the mimicry was. While many species of cuckoos and predators may populate large stretches of the wild, the species within narrower geographical niches are fewer and more specialized. Cuckoos thus evolve to mimic only the most local predatory birds. “There is no benefit in looking like a dangerous species your target is not familiar with,” Gluckman said in a release that accompanied the study.

While cuckoos don’t win many respectability points for posing as something else, hawks aren’t entirely blameless either. The African cuckoo-hawk, after all, got its name because of its striking similarity to something it’s not—almost more cuckoo than hawk. And when the Cambridge team ran their spectral pattern study, that similarity held up in the bird’s-eye view too. Cross-species mimicry, it seems, can be a two-way street.

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