"Western" Flycatchers in Washington and BC

Eugene Hunn enhunn at Home.com
Thu Jun 7 18:07:50 PDT 2001


I was one of those who queried Andy about the "Pacific-slope Flycatcher" on
the Grande Ronde River in Asotin Co. The Western Flycatcher (Empidonax
difficilis) was split by the AOU in 1998 into Pacific-slope (E. difficilis)
and Cordilleran (E. occidentalis) Flycatchers, based on the research and
argument of Ned K. Johnson, UC Berkeley professor and senior member of the
AOU checklist committee. The relevant evidence is essentially that published
in Johnson's monograph, "character variation and evolution of sibling
species in the Empidonax-difficilis-flavescens complex," UC Publications in
Zoology, Vo. 112 (1980) [some later published genetic evidence was equally

A map of the ranges of the various "sibling species" is shown on pg 12 of
Johnson's monograph. Incredibly, there is a large blank area separating the
Pacific-slope Flycatcher populations of the coastal and Cascade-Sierra zone
from the Cordilleran Flycatcher populations of the Rocky Mountains and Great
Basin ranges, excepting only a narrow zone of contact on the
California-Oregon border. In fact, there are breeding populations of Western
Flycatchers all across this region in appropriate habitats. In short, the
map indicates that there are no intervening populations between the east
slope of the Cascades in Washington and southernmost BC (which he considers
Pacific-slope) and the northern Rocky Mountain populations in nw Montana and
se Alberta. He explicitly includes populations from southeastern
Washington -- the Palouse and the Blue Mountains -- as a Cordilleran
Flycatcher population, which he distinguishes as the "Northern Volcanic
Region subpopulation" (pg. 15-16), to which he ascribes some intermediate
characteristics. He includes a sonograph of males (#25, Whitman County,
Washington; male position note, pg. 69; male advertising song, J, Palouse
River, 2200 ft, 2 1/2 mi N and 3 mi W Palouse, Whitman Co., Washington, pg.
62) from near Pullman which he treats as examplars of this Cordilleran
Flycatcher subpopulation. He also indicates three "breeding specimens" from
this region on his map.

Johnson clearly states that the male position note (typically a single
sharply upslurred whistle in Pacific-slope Flycatchers; a distinctly
two-parted whistle in Cordilleran) is not definitive, as Cordillerans, at
least, may give Pacific-slope like notes. He argues that only the full
advertising song is difinitive. In this he focuses on the third syllable of
the three syllable song: "In syllable 3, which is usually composed of two or
three obvious notes on the spectrographic trace, the frequency sequence of
low-high, of the loudest notes of coastal birds..., becomes reversed to
high-low in the far-interior birds" (pp 65-66). There are also qualitative
differences in the second syllables. In any case, birds I have recorded in
Walla Walla, Columbia, and Whitman Counties have shown the Cordilleran song
features. However, a sample of 30+ songs recorded by myself and Richard
Cannings across northern Washington and southern British Columbia exhibits
clinal variation in the features Johnson considers criterial.

In short, I believe the AOU erred in splitting the Western Flycatcher, given
the inadequacy of Johnson's coverage of the northern portion of the range of
this species complex. However, if we grant the AOU the power to decide what
is and what is not a species, we are forced to accept the southeastern
Washington Western Flycatchers as "bona fide" Cordillerans.

Also, note that Sibley's Pacific-slope Flycatcher range map is in error,
indicating that the se Washington birds are Pacific-slope, which is not what
Johnson and the AOU have decided.

Gene Hunn.

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