Some hummingbirds avoid harassment by changing plumage

An adult female white-necked Jacobin hummingbird is no stranger to invisible labor.

When she lays an egg, the male hummingbird who played an equal role in the conception of said egg is nowhere to be seen. It is only thanks to her hours of weaving that the egg has a nest at all. When her chick hatches, she alone will feed it regurgitated food from her long bill.

And then there is the constant harassment. As the muted-green females visit flowers to sip on nectar, they are chased, pecked at and bodyslammed by aggressive males of their species, whose heads are a flamboyant blue.

But some female whitenecked Jacobins, which are found from Mexico to Brazil, have a trick up their wing: Instead of garbing themselves in green plumage, they take on bright blue ornamentation and appear essentially identical to male hummingbirds. Scientists found these male look-alikes avoid harassment directed toward green females, according to a paper published recently in the journal Current Biology.

For the past 50 years, most scientists have relied on the theory of sexual selection, or mate choice, to explain why so many male birds have bright plumage, said Jay Falk, a postdoctoral researcher at the University of Washington and an author of the paper.

But these theories can disintegrate when applied to female birds, which can evolve ornamentation of their own for evolutionary advantages that have nothing to do with seeking male mates.

Food seems to be the ultimate driver of female ornamentation in white-necked Jacobin hummingbirds.