Ok, in truth, there is nothing sad about today. It’s a bright, blue crisp morning out there. The rain and wind of the past couple days washed at least some of the pollen away. There’s a lot to enjoy out there today. So not a sad post. It’s actually a post about a bird I’ve neglected a bit- the Mourning Dove. I see them every day- perched on telephone wires, in trees, flying around campus. They really are quite common. On the flip side, though, there’s not a lot that they do to draw attention to themselves. Well, there was one time when one sat on top of the chimney and its flutey call echoed through my fireplace. Other than that, though, they’re pretty discreet.
Now, as you may have noticed, I spend quite a bit of my time thinking about sounds. I’m not sure what put this particular thought in my mind this morning- I must have heard a couple doves on my run. Doves make sounds other than their call. One of their most recognizable sounds is also not a vocal sound, it’s a mechanical one. Anytime you see a Mourning Dove (or even a pigeon) take flight, you can hear a pulsing sort of whistle sound. In Mourning Doves, this sound is called a wing whistle and it is produced by the movement of air over the feathers of the wing. From my perspective that sound is useful. When I hear it, I know there’s a dove nearby without having to see it. It is immediately recognizable to me. Of course, if I can pick up on it, so can others! So I started wondering if anyone had looked to see whether or not the wing whistles of doves were actually used as a source of information by other birds. What I found was actually quite cool!
Two different studies show that wing whistles in different kinds of birds (one in the Mourning Dove and one in the Crested Pigeon, a species in the same order) are used by other individuals as a way to respond to potential threats. In fact, in both cases, other birds were able to differentiate between the wing whistle produced in response to a threat versus one produced in normal take-off. The angle of ascent during take-off in response to a threat changes aspects of the whistle and birds can pick up on that. In the Crested Pigeon, the researchers found that it was aspects of the whistle itself, not just volume that triggered the response in other birds.
In Mourning Doves, things get even cooler. Not only do other doves make the same differentiation between a startle whistle and a regular whistle, but so do other birds. The researchers used playbacks of recorded whistles and found that Northern Cardinals and House Sparrows both increased their own vigilance after the playback of startle whistles, but not after the playback of other sounds. What a handy warning system to have!
So, other birds have learned to cue into the mechanical process of flight in the Mourning Dove to get information about what’s going on around them. I may have neglected these poor doves, but everyone else was apparently paying close attention.