I don't have a theory but my censuses here in bellingham this spring show that
they arrived about April 12 and began singing immediately. Numbers built up to
about 12-16, until May 17 when they slowed and continued to decrease until
yesterday when i saw 2 but heard none.I suspect that they stopped singing when
nesting began but have no proof (the same pattern is seen in Black-throated gray
, Townsend's, and most pronounced in Common yellowthroat.
Clark Blake, Dept. of Geology, WWU