Whistling Wings

For the first couple of years of living out here in the woods, I thought that the sound a mourning dove makes when it takes to flight was a kind of excited song—sounding like a repeated “fwee-fwee-fwee.” After getting more acquainted with this member of the pigeon family (Columbidae), I realized that the sound was not coming from its beak, but was an airy whistle emanating from its wings, as it beats the air on takeoff.

Over the years I’ve gotten used to this sound. It’s an indication that doves are flying about, without my having to look up to verify their presence. They announce themselves very uniquely. The wing flaps of most songbirds, in contrast, are pretty quiet—you have to be within several yards of them to hear their wings beating. In fact, large predatory birds like owls have nearly silent wings—quiet enough to swoop down on prey without warning them. They are true stealth birds.

A question came to my mind recently: What evolutionary advantage might there be to the dove’s whistling wings? It’s obviously an evolutionary advantage to the owl to have silent wings—any ancient owls who experienced a genetic mutation for wings that made a noise would have immediately died out, while the quiet-winged owls survived. That’s how evolution works.

So why do doves have noisy wings? Well, to begin with, a dove’s diet consists solely of seeds and grain, so the bird doesn’t need to worry about warning a seed that it’s about to pounce on it. OK, no need to stay quiet for that reason, but I couldn’t imagine any advantage to whistling wings—or any reason why doves would evolve them because they were useful. So what’s going on?

It occurred to me that maybe there is no advantage. Could it be that their wings evolved as they have, for some other advantage—and those wings just happen to whistle? In a similar fashion, the peacock’s tail is this magnificent thing that certainly does not give it the most graceful flight skills. But the peacock puts up with the cumbersome tail because the peahen likes the look of it and he damned well better look fancy, if he wants to win her eye. That’s a case of sexual selection trumping flying skills.

A little research into dove characteristics, in an attempt to solve the whistling wing question, gave me two relevant facts. One, the dove’s bill is not hard, like a finch. It can’t bash or crunch the seeds it swallows with that soft bill, so it swallows the hard seeds, sending them down into its crop, where they get ground up by gravel, to reveal the seed’s nutritious interior. Second, when a dove gets into an altercation with another bird, it doesn’t attack with its beak like other birds do (remember that tender bill of theirs), but beats at its foe with its wings.

So maybe that’s my answer: a dove’s wings have evolved to be these tough devices that can be used to go into battle, as well as to fly. And it so happens that tough dove wings whistle. So the evolutionary advantage is not the whistle, it’s the strong wings to fight with. These wings just happen to whistle, which is no disadvantage for the dove, so the whistle endured. Sounds reasonable, although there may be more to the story than that. I’ll just keep on watching and researching and maybe I’ll eventually tease the whole story out.