Thanks for the question, Jim D. in Delvan, WI.
Answer:
Perhaps the reason relates to how it’s often easier to hear than see them, as Hermit Warblers typically forage individually high in the tree tops — hence, the common name that John Kirk Townsend first described when collecting this species in 1837 near Fort Vancouver (now Vancouver, WA).
Considered part of the Black-Throated Green “super species” — along with Black-throated Green (Dendroica virens), Golden-cheeked (D. chrysoparia), Black-Throated Grey (D. nigrescens) and Townsend’s (D. townsendi) warbler — the Hermit Warbler breeds in coniferous forests of the Coast, Cascade, and Sierra Nevada mountain ranges of southern Washington, Oregon, and central and northern California.
Where it occurs with Townsend’s Warbler within the s. Washington Cascade Mtns., Olympic Mtns., and central Oregon Cascade Mtns., Hermit Warbler may be losing populations as it is replaced and outcompeted by its first cousin. Studies by S. Rowher and C. Wood from 1994 to 1996 in this region indicate that 80 percent of adult Townsend’s and only 53 percent of adult Hermit paired and maintained their territories long enough to reproduce successfully. Other data relating to aggression behavior and hybrid zone analyses further supports Rohwer and Wood’s conclusions. Another reason for the reduced local populations of Hermit’s may be the result of reduced suitable breeding habitat in portions of its home range.
Nonetheless, in other portions of its range where Townsend’s Warbler does not breed, Hermit Warbler population densities appear to be stable, according to Breeding Bird Surveys (BBS) conducted in the last 30 years. However, it’s important note that BBS surveys are limited to routes where roads occur, so more comprehensive surveys of the Hermit’s total abundance do not exist. In addition, given the Hermit Warbler’s inherent small population worldwide and narrow geographic distribution, it is not considered abundant or common in most portions of its home breeding range.
