We Finally Solved the Mystery of Why This 'Boring' Bird Has Such Colorful Chicks

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Why are coot chicks so much flashier than adults?. Casey Klebba [CC BY-SA 4.0]/Wikimedia Commons

The American coot is a ubiquitous bird often seen waddling across the surfaces of North America's ponds and lakes. Their plumage is rather forgettable; a plain-black coloring that often blends with the murky waters where it swims.

This unadorned look is all a ruse, however. Coots are hiding some rather mischievous behavior under that boring veneer, and while the adults can hide it well, it's written all over the feathers of their chicks, reports Phys.org.

Scientists have long been befuddled by the discrepancy between the colors displayed by coot chicks and coot adults. Unlike their parents, chicks are born with fiery-orange feathers, beaks and skin. Their flamboyancy seems to go against common evolutionary logic. Usually, colorful plumage in birds is utilized as a mating display; better-ornamented adults (most often males) are more likely to attract mates, and thus pass down their genes to the next generation.

But that can't be what's happening with coot chicks because they lose their colors by the time they reach sexual maturity. Furthermore, chicks are typically more vulnerable to predators than adults are, so shouldn't that brilliant colorization make them even more susceptible to catching the eye of a hungry carnivore?

But now, scientists think they've solved the mystery, and the explanation hints at these birds' hidden wild side.

In a study published in Proceedings of the National Academy of Sciences, researchers explain how coot chick ornamentation was found to correlate with the order in which those chicks hatched. Coot hens lay about 10 eggs, one per day, and the eggs usually hatch in the order in which they were laid. It turns out that the later a chick hatches, the more colorful it is.

Why should this weird correlation exist? The researchers realized it was a clue. For one, it indicates that it's not the chicks that are "choosing" their colors; it must be their mothers.

"That tells us the chicks can't be controlling their coloration, because they don't know where they are in the laying order. This is a maternal effect, presumably due to the mom putting more carotenoid pigments in the later eggs," explained Bruce Lyon, first author of the study.

Further observation of coot nesting and laying behavior helps to reveal why it might be useful for coot mothers to color-code their chicks. Turns out, coots utilize a roguish parental tactic known as brood parasitism. They lay a number of eggs in the nests of other coots in an effort to fool them into raising their chicks for them. They typically do this with the first few eggs they lay, reserving the later eggs for their own nests.

So, the color coding can help them to identify which chicks are more likely to be their own, and not the orphans of some other sneaky coot. Researchers confirmed this strategy by noting how coot parents tend to pick favorites, making sure that the most colorful chicks are also the best fed.

Coot breeding is a labyrinthine world, where these drab birds hide their true colors, secretly attempting to pull one over on each other.

"They're complicated birds. For over 20 years, we've been chipping away at understanding their reproductive behavior, and this is another interesting aspect of that," Lyon said.

Further research into the genetics of this strategy should help to reveal the evolutionary logic behind it. How often are coots tricked into favoring chicks that aren't their own? The color-coding fail-safe must falter sometimes, otherwise it wouldn't make much sense for coots to go through with the whole bait-and-switch game to begin with.

At the very least, the research shows that these birds have a lot more going on than their appearance might first suggest.