8Michael,
As I know them the mid-elevation North Shore Mtns north of Vancouver BC are
very heavily clothed in silver fir (Abies amabilis), very favorable habitat for
Townsend's Warblers in my experience. Possibly we should not be thinking about
elevation here but rather precipitation and vegetation zones; they are
different in the two areas, elevation for elevation. I suspect vegetation at
3,800' on the North Shore Mts, is similar to about 5,000' in eastern King
County. The North Shore Mtns are well-known to be an area of copious precip.
(130-140" at 5,000'), eastern King County seems noticeably drier ( maybe only
about 100" annually!). Yellow-rumps in Doug fir etc at lower levels makes
perfect sense to me. However, Yellow-rumps are also at least fairly common as
breeding birds above 4,500' on the North Shore Mountains in the subalpine zone
where the forest becomes less dense and is characterized by tree clumps of mtn
hemlock, subalpine fir.

Andy Stepniewski
Wapato, WA