For the Birds Radio Program: Gone with the Wind: White-throated Sparrows
It’s easy to understand the complex mating system of White-throated Sparrows if you remember the book or movie, Gone with the Wind.
This fall I’ve been getting a lot of White-throated Sparrows at my feeder, and for the first time ever, I have a large population of eastern chipmunks, too. I’ve long noticed that white-throats have chipmunk-like striping, but never until this year of plenty have I noticed how uncanny their similarities are. The striping provides effective camouflage to protect both of them from hawks. Even though I live right under Hawk Ridge, I have only once seen a hawk capture one of my sparrows and never a chipmunk.
White-throats often make a sharp chink call when alarmed. We hear this a lot simply because the birds are alarmed by our presence, and we often find the calling bird perched conspicuously, flicking its tail. When chipmunks make their noisy alarm call, they often flick their tails, too.
Sometimes white-throats make a seep call, usually while hidden in vegetation, making it hard for us to figure out where the heck they are, though oddly, this is the call they use to announce their location to one another. White-throats are most famous for their spring song, the whistled “Old Sam Peabody, Peabody, Peabody.” Every now and a burst of hormones sets them to singing even in the dead of winter, but right now songs are few and far between.
White-throated Sparrows and chipmunks share more than appearance and chip calls-these striped ground feeders have an almost identical diet of seeds, small fruits, and insects. The one fundamental dietary difference is that chipmunks also eat bird eggs, including those of White throated Sparrows. As similar as the two species are ecologically, this one discrepancy explains why the littler sparrows so often fly at the bigger chipmunks to drive them away.
Chipmunks all look pretty much the same to me, and their behavior isn’t what you’d call “novel.” But White-throated Sparrows have several storybook qualities. They come in two color types–one with white head stripes, the other tan stripes. The differences in color have nothing to do with sex–half the males are tan-striped, and half the females are white-striped. Intriguingly, virtually all pairs include a male of one color and female of the opposite color. And equally intriguingly, the color-types correspond to specific behavior types. White-striped males tum out to be avian Rhett Butlers-they’re exceptionally good looking and aggressive but have a wandering eye, and engage in what many ornithologists refer to as “extra-pair copulations.” Meanwhile, female white-stripes are more domineering than tan-striped females, even singing frequently, and don’t make very attentive mothers-these are the Scarlett O’Hara’s of the bird world. The white-striped of either sex is dominant over the tan-striped form of the same sex.
Females of either color form prefer tan-striped males-the Ashley Wilkes’-type gentlemen more likely to stay home and help with the children, while males of either color can’t help but gravitate to the Scarlett O’Haras. But unlike the Old South, in the world of birds, females are the ones who get final say on mates, and the white-striped females lay claim to virtually all the tan striped males. So ultimately Scarlett gets her Ashley, and Melanie ends up with Rhett. Although there are no absolutes in the natural world, this mating system, referred to by scientists as negative assortative mating, occurs in fully 96% of all the many pairs studied by various researchers from 1968 through 1993. It’s not quite the way Margaret Mitchell fashioned her novel solution but watching them provides us with plenty of entertainment until the last White throated Sparrows fly away for the season, gone with the wind.