eWestern Birds

Toward Clarifying the Wyoming Ranges of the Vireo gilvus Complex

M. Ralph Browning

ABSTRACT: The Warbling Vireo (Vireo gilvus), generally recognized as one polytypic species, is widely distributed across North America, but differences in morphology, song, genetics, and ecology suggest the western and eastern populations may represent two species. Understanding their distributions enables tracking of range changes and other factors that might affect the conservation of populations. Therefore, I studied museum specimens, specimen data, and identifications provided by investigators recording songs to help clarify the ranges of the two taxa in Wyoming. Of 18 specimens in the U.S. National Museum collected from 1858 to 1930, I identify 15 as the western species V. swainsoni. These are spread over most of Wyoming, east to Crook and Albany counties. Only three represent the eastern species V. gilvus, two from Greybull, Big Horn Co., and one from Cheyenne. Whether the overlap represents sympatry of breeding populations in eastern Wyoming or overlap in migration remains to be determined.

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