What geological feature or environmental boundary reinforces the Western Tanager's distinct western lineage, as it is generally absent as a consistent breeder east of this demarcation?

Answer

The continental divide

The distribution pattern of the Western Tanager strongly suggests that specific geographic barriers played a role in solidifying its unique evolutionary path in western North America. The species is a consistent breeder throughout the coniferous forests spanning from Southern British Columbia down through the Rocky Mountains and the Sierra Nevada. Crucially, the uniformity of this distribution shows that the species is generally absent as a consistent breeder east of the continental divide. This suggests that significant barriers, potentially including the expanse of the Great Plains or the eastern limits of major western mountain systems, served to isolate this lineage, allowing it to specialize without interbreeding or gene flow with eastern populations, if any existed.

What geological feature or environmental boundary reinforces the Western Tanager's distinct western lineage, as it is generally absent as a consistent breeder east of this demarcation?

Related Questions

To which family does DNA evidence definitively place the genus Piranga, including the Western Tanager?Which relative species within the Piranga genus is noted for being largely non-migratory, remaining in the southwestern US and Mexico year-round?What specific combination describes the male Western Tanager's striking fresh spring plumage?What geological feature or environmental boundary reinforces the Western Tanager's distinct western lineage, as it is generally absent as a consistent breeder east of this demarcation?After which developmental event does the Western Tanager acquire its distinct, bright adult male plumage?What were the primary morphological and behavioral characteristics used historically to group the Western Tanager with South American true tanagers?How is the female Western Tanager generally described in terms of coloration when contrasted with the male's vibrant display?To which lower-elevation regions does the entire population of Western Tanagers migrate to escape harsh northern winters?What primary evolutionary function is served by the female Western Tanager's less conspicuous, drab camouflage coloration?What specific type of forest habitat, often found at high elevations, does the Western Tanager utilize for breeding across the western mountains?
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