How the Cuckoo Wages an 'Evolutionary Arms Race'

Clever birds figure out how to trick others into raising their kids

— -- There's nothing stupid about the cuckoo bird. It's a nasty cheat that sometimes leaves its eggs in another bird's nest so someone else can raise its chicks, and it is one of nature's best performers of trickery and deceit, but it's definitely not stupid.

Some members of this family of about 142 species are engaged in what scientists are calling an "evolutionary arms race" to see which birds can outwit the others.

Evolutionary biologist Mary Caswell Stoddard of Harvard University and colleagues Rebecca Kilner and Christopher Town of the University of Cambridge have found that some cuckoos have developed the ability to produce eggs that are a perfect match for the eggs produced by other members of the family. That's to convince the host that the foreign eggs really are hers so she won't toss them out of the nest.

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But meanwhile, some prospective hosts have figured out how to produce eggs that are distinctly different, even from eggs laid by other members of the family, so they will quickly recognize any uninvited guests.

"The ability of common cuckoos to mimic the appearance of many of their hosts' eggs has been known for centuries," Stoddard said in releasing the study, published in the journal Nature Communications. "The astonishing finding here is that hosts can fight back against cuckoo mimicry by evolving highly recognizable patterns on their own eggs, just like a bank might insert watermarks on its currency to deter counterfeiters."

Other researchers have found that cuckoos are more sensitive to incredibly subtle differences in colors, so the mimicry has to be right on target to work. You or I wouldn't be able to tell the difference between the host's eggs and those left behind by an interloper.

The scientists used the latest in recognition technology from computer science to find out how eggs can differ in ways so finely tuned that even a mother won't be sure which ones are hers.

The technology, which they call NaturePatternMatch, can detect differences in patterns that are far too subtle for us to see. It's based on the face recognition technology that allows a computer to determine if a person is really who he or she claims to be, which is useful in situations that demand the highest level of security.

The researchers are primarily interested in evolution as a whole, not just among cuckoos, and they found that these birds "have evolved effective signatures in diverse ways," so there are apparently many ways that an organism can master deceit.

But to be fair, not all cuckoos are cheats, and they aren't crazy. The name "cuckoo" comes from the sound it makes, not its IQ or quirky lifestyle.

Many old world species commonly engage in parasitic practices throughout Europe, Asia and Africa, but most species found in North America do what we tend to think all birds do, nurture and raise their own kids.

One of the best known cuckoos in the U.S. is the greater roadrunner, seen throughout the deserts of the Southwest. Like many cuckoos, it will sometimes enjoy a salad, but it loves meat and to some species it is the most feared predator on the planet. But despite its reputation as a killer, both the male and female parents share the responsibilities of caring for their brood.

But even the roadrunner can be a clever deceiver. These birds, somewhat larger than many other cuckoos, have been observed teaming up to take on a rattlesnake. One bird will distract the deadly snake while another sneaks up behind it and grabs it by the throat.

The roadrunner then beats the snake's head against a rock to kill it before both birds sit down for lunch. It's not a pretty scene, but even these fearless meat eaters can be model parents.

That's not always the case with the yellow-billed cuckoo and the black-billed cuckoo, which only occasionally parasitize another bird's nest. But apparently even that isn't working out for the yellow-billed bird. It is nearly extinct in the western United States.

By the way, these two species love cicada outbreaks and show up in droves to join in a feeding frenzy. But after that, it's back to a diet of caterpillars, grasshoppers and tree frogs.

The Anis cuckoo, seen throughout much of the United States, is more social than most species. They have been known to share nests so that several birds can lay eggs and all take part in raising the kids. Nests have been found with up to 20 eggs, with as many as four mothers, and harmony rules until there is a shortage of food.

When that happens, the dominant female starts tossing eggs out of the basket, especially those that are not her own, until the brood is small enough to survive on whatever food is available.

So even in the best of times, cuckoos have found a tough way to earn a living. Deceit, though not pretty, may be the only way to go.