WESTERN BLUEBIRDS-- MIGRATORY OR RESIDENT?

Wayne C. Weber contopus at shaw.ca
Fri Mar 15 08:44:10 PST 2002


Michael, Gene, and Tweeters,

The main thing I was trying to suggest in my previous message was that
the WESTERN BLUEBIRDS reported at Juanita Bay Park could have been
locally-wintering birds-- not necessarily newly arrived migrants,
although the latter is at least equally likely.

Michael's comments that Juanita Bay is "nowhere near known nesting
areas for Western Bluebird" does not totally agree with the
information I have. The book "Breeding Birds of Washington State"
shows confirmed breeding localities in the Carnatian-Duvall area and
in south-central King County. There is also a sizable and widespread
breeding population in Pierce and Thurston Counties. Maybe my
definition of "near" is not the same as Michael's.

Do the birds from Pierce & Thurston Counties all head south in winter?
If so, I would be surprised, because Western Bluebirds in southern
B.C., both coastal and interior, are (or were) at least partly
resident. I also had the impression that they were largely resident in
the Willamette Valley of Oregon, where they are fairly common (Perhaps
Mike Patterson could enlighten us here?)

The Western Bluebird population on southern Vancouver Island and the
Gulf Islands of BC-- which died out completely during the 1980s-- was
largely resident, as indicated by Christmas Bird Counts at Victoria as
high as 59 birds in 1964 and 55 in 1959.

In the Okanagan Valley of BC, probably 80% or 90% of Western Bluebirds
go south in winter, but the Penticton CBC usually tallies 20 or 30
every year, with a high of 61 in 1995.

In the southern B.C. interior, Western and Mountain Bluebirds
generally breed in different habitats (grassland and grassland edges
for Mountain Bluebirds, open pine forest for Westerns). I have seen
many large flocks of migrating Mountain Bluebirds, but have never seen
Westerns in with them, although I know of a few reports of mixed
flocks. Mountain Bluebirds usually arrive before March 10th in the
Okanagan Valley, although the peak migration is in late March and
April. Western Bluebirds (according to Cannings et al. in Birds of the
Okanagan Valley) usually arrive about a week or so later than the
first Mountains, with an average "arrival date" of March 18.

In the Vancouver area, Mountain Bluebirds are scarce but regular
spring migrants, with an average arrival date of April 1, varying from
March 6 to April 25 (18 years' data). Western Bluebirds have been seen
there only about 5 times in the last 30 years, although they bred
there prior to the 1960s.

So I don't believe Western and Mountain Bluebirds generally migrate
together, although they may do so in some cases.

The Western Bluebird is certainly an intriguing species. Its
disappearance as a breeding bird from most of western Washington and
southwestern B.C. in the last 50 to 60 years is unexplained, and
probably not mainly a result of Starling competition, because most of
the decline occurred before Starlings arrived. (I know that Russell
Rogers and others have given considerable thought to the reasons for
the decline.) I agree with Michael that there is "a need for much more
data"-- we should be carefully monitoring the status of this species.

Wayne C. Weber
Kamloops, BC
contopus at shaw.ca


----- Original Message -----
From: Michael Hobbs <Hummer at isomedia.com>
To: Wayne C. Weber <contopus at shaw.ca>
Cc: Tweeters (E-mail) <TWEETERS at u.washington.edu>
Sent: Thursday, March 14, 2002 4:17 PM
Subject: Re: Western Bluebird -- arrival date?


Wayne - Data are scant, but this year's sighting at Juanita and last
year's
sighting at Marymoor are nowhere near known nesting areas for Western
Bluebird. Whether this represents a small amount of migration west of
the Cascades, or whether this is some kind of pre-breeding
exploration, it would seem reasonable that there be some seasonality
to this movement.

The biggest assumption I made is that it might be related to Mountain
Bluebird movements, which I don't expect (based on Marymoor data) to
begin here until next week. Western and Mountain Bluebirds winter
together in some areas (i.e. New Mexico) where they do not breed, and
breed in some areas (B.C.) in which they do not winter. So it seemed
possible to me that they might migrate between those locations
together. Townsend's Solitaire might also be part of this movement,
conceivably.

A huge leap, perhaps, which clearly points to a need for much more
data.

Michael Hobbs
Kirkland WA
hummer at isomedia.com





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