Painted Bunting is an unusual bird, and not just because of the adult male’s vivid colors. It’s the only migratory songbird in North America that occurs in two isolated regional populations.
One breeds in the southern Midwest of the United States, in Kansas, Oklahoma, Texas, Arkansas, and Louisiana. The other is smaller, and limited to coastal portions of North and South Carolina, Georgia, and northern Florida.
Painted Buntings rarely breed in the gap that lies between the western and eastern ranges. Birds from the different regions migrate and molt at different times and spend the winter in separate locations, and the two populations are not known to come into contact. Curiously, though, Indigo Bunting, a closely related species, breeds not only in the western and eastern regions but also in between.
Scientists have long wondered whether some particular combination of landscape variables makes the gap acceptable to Indigo Bunting and unsuitable for Painted Bunting. But when researchers tested the idea recently, their computer models predicted a single contiguous breeding range for both species, not two.
So what caused the Painted Bunting’s breeding-range gap?
The likeliest explanation, write biologists J. Ryan Shipley, Andrea Contina, and colleagues in the July 2013 issue of The Auk, is that the split originated tens of thousands of years ago, in the Pleistocene, when glaciers limited how far north Painted Bunting bred and the Gulf of Mexico divided the species’ breeding range.
Presumably, the species shifted its range northward as the glaciers receded, but because of the rigors of migrating over or around the Gulf, the divided populations remained separate, giving rise to isolated breeding ranges and the intervening gap we know today.
A version of this article appeared in the December 2013 issue of BirdWatching.
Read the abstract:
J. Ryan Shipley, Andrea Contina, Nyambayar Batbayar, Eli S. Bridge, A. Townsend Peterson, and Jeffrey F. Kelly, 2013, Niche conservatism and disjunct populations: A case study with Painted Buntings (Passerina ciris), The Auk, Vol. 130, No. 3 (July 2013), pp. 476-486. Abstract.