Michael,

It is obvious that something very strange is going on with BTGWs
and TOWAs on Vancouver Island. My experience over several decades is
that I can correctly distinguish BTGW from TOWA by song about 90% of
the time; that is, there are only about 10% that I miscall, based on
hearing the song first and seeing the bird later. This experience has
nearly all been on the mainland. I rarely hear "unbuzzy" BTGW songs.
You are aware that much of the older literature states that BTGW
does not breed on Vancouver Island. It appears that BTGW has only
become a common breeding bird on V.I. in the last 30 to 40 years (or
less). This might have something to do with why they seem to be
hybridizing with TOWA on V.I., but not elsewhere.
I am also surprised that both species seem to be breeding at low
altitudes in 60-80 year old stands of Douglas-fir. On the southern
B.C. mainland, although there is some habitat overlap, such forests
would not normally have breeding BTGWs. BTGWs breed in deciduous
stands, mixed second-growth stands of alders and conifers, but not
usually in pure conifer stands, unless these have many openings. TOWA
breed mainly at higher altitudes than BTGW ( they are commonest at
2000 feet plus), although they do breed down to sea level where there
is old-growth or late seral conifer forest (e.g. Lighthouse Park, very
locally in Stanley Park).
The hybridization situation with TOWA and HEWA is well known and
has been well studied. However, it comes as a surprise to me that TOWA
and BTGW are hybridizing anywhere, although I admit that I haven't
been keeping up with current ornithological literature like I used to.
Can anyone provide further insight on this situation, especially
the occurrence and extent of hybridization between BTGW and TOWA?
I am copying this message to Dr. Michael Morrison, who I know has done
major research on this group of warblers. Perhaps he or others can
help to put this in perspective.

Sincerely,

Wayne C. Weber
114-525 Dalgleish Drive
Kamloops, B.C. V2C 6E4
Phone: (250) 377-8865
wayne_weber at bc.sympatico.ca



-----Original Message-----
From: Michael G. Shepard <mgs at orcatec.com>
To: 'S. Downes' <sdownes at u.washington.edu>; Fred Sharpe
<fsharpe at sfu.ca>
Cc: tweeters at u.washington.edu <tweeters at u.washington.edu>
Date: Sunday, May 23, 1999 8:03 AM
Subject: How about the songs and calls of Black-throated
Gray/Townsend's hybrids?


>Greetings,
>
>I've been following the discussion on HETOs, and would like to throw
>another combination into the pot. Hermit Warblers and associated
hybrids
>are virtually non-existent in our area. Instead we have the
following
>problem to deal with.
>
>Over the past few years, while censusing forest songbirds on eastern
>Vancouver Island, I've been having difficulty separating the songs of
>Black-throated Gray and Townsend's Warblers. In my study area near
Duncan,
>both species are occurring together in 60-80 year old stands of
>Douglas-fir, and their songs are often indistinguishable. Some of
the
>Townsend's have the nice clear ending as they are supposed to, but
most of
>the Black-throated Grays have very unbuzzy songs. I rarely hear the
buzzy
>song so typical of mainland Black-throated Grays.
>
>I have a strong suspicion that a substantial proportion of the birds
may be
>hybrids. We are now catching hybrids annually at the Rocky Point
>Migration Monitoring Station at the southern tip of Vancouver Island.
A
>few are distinctly intermediates, while most are Black-throated Grays
with
>a few Townsend's characteristics such as greenish backs or yellow
flecks on
>the breast.
>
>Is anyone else seeing or catching these types of hybrids?
>
>Michael G. Shepard
>Director
>VGI Vision Foundation
>5325 Cordova Bay Road, Suite 211
>Victoria, BC V8Y 2L3
>(250) 658-4844 telephone
>(250) 658-0084 fax
>mgs at orcatec.com
>http://www.visionfoundation.org
>