SEATTLE, Aug. 25 (UPI) -- Hormones make Townsend's warblers more aggressive than other warblers, giving them the advantage in turf battles and mating, U.S. scientists said.
University of Washington researchers studied levels of testosterone and dihydrotestosterone in male Townsend's and in their kin species, hermit warblers, in Washington state. The songbirds live in the damp Douglas fir forests of Western North America.
Researchers found substantially higher levels of the hormones in Townsend's warblers than in hermit warblers, which may explain the aggression that for thousands of years has given Townsend's the upper hand in competing for territory and mates, researchers said.
The hermit warbler now is mostly confined to coastal forests in Washington, Oregon and northern California, and current trends show hermit warblers probably will become extinct in 5,000 years, researchers said.
A Townsend's warbler is small with yellow and black streaking on its sides and a dark crown, throat and upper breast. A hermit warbler has a yellow head and a dark chin and throat, but its dark feathers are much less dominant and its appearance is less striking.
