White-striped white-throated sparrow, photo by USFWS Midwest
“Old Sam Peabody body body body.” So the song goes. It was the first bird song mnemonic that I learned. I learned it while up north, on Wisconsin's Long Island on the shores of Lake Superior. It took me an embarrassingly long time to figure out that song. As I monitored the endangered piping plovers on Long Island's sandy shores, the white-throated sparrows seemed to follow and mock me. I had uncovered the identity of the white-throated sparrow, but as it turns out the bird's identity is much more complex than its name.
These sparrows exhibit polymorphism, with four possible identities that they assume for life. Males and females may be either white-striped or tan-striped on their crown. These differences in phenotype have huge implications for the sparrows, and shape their social interactions and even habitat selection.
White-striped birds will aggressively defend the nest, sing much more frequently, and the males will copulate with multiple female partners. White-striped females will copulate multiple times with their male counterparts. The white-striped males' breeding territory includes more open forest canopy. For these reasons, the birds I heard on Long Island—which called all day amid the open pine forests, bogs, and dunes on the island—were almost certainly white-crowned males.
White-striped white-throated sparrow, photo by Kelly Colgan Azar
The tan male birds tend towards denser forested habitat, sing less, and spend more time on the nest taking care of young.
To complicate things, opposites attract in the world of white-throated sparrows. Females of both types prefer tan-striped males, and the aggressive white-crowned females will quickly pair with the tan-striped males. That leaves the white-striped males to mate with the tan-striped females. This is known as dissasortative mating, where opposite genotype/phenotypes mate more often than would be expected randomly. In white-throated sparrows, this mating maintains the polymorphism in about equal proportion of white-striped and tan-striped birds.
Tan-striped white-throated sparrow, photo by Kelly Colgan Azar
All of this information was gathered through simple ornithological research, conducted analyzing museum specimens and following hundreds of live birds. This simple research revealed intriguingly complex social lives in white-throated sparrows and allowed scientists to test for a genetic basis of the differences, which exists due to a chromosomal inversion.
You can find white-throated sparrows migrating through Faville Grove soon. They prefer some type of forest cover, but can be found in brushy edge habitat as well. These birds are recognizable as winter feeder birds during a Wisconsin winter, but at that time it's very difficult to tell the difference between tan-striped and white-striped birds. The simple and folksy song of the white-throated sparrow belies its remarkable life history, a truly fascinating discovery of science. You can read more about this bird in Ken Kaufman's Notebook, which delightfully delves into the nuance of different bird species and is accompanied by wonderful illustrations.
Written by Drew Harry, Faville Grove Sanctuary land steward
Header photo by Kelly Colgan Azar
