Subject: MORE ON MIDWINTER BARN SWALLOWS
Date: Jan 23 13:11:30 2002
From: Wayne C. Weber - contopus at shaw.ca


Birders,

The discussion on this subject on OBOL and TWEETERS has been fast and
furious. I would like to add a few more thoughts on the subject.

While the number of reports of midwinter BARN SWALLOWS in Washington
and Oregon this year may have been an all-time record, such was not
the case in southwestern B.C. So far this year, the only reports I am
aware of were up to 2 birds at Iona I., Jan. 5 to 15, and one bird at
the Reifel Bird Sanctuary on Jan. 13. A MUCH larger influx occurred
in February 2000. Some of the BC records for February 2000 are as
follows:

Feb. 7 to 10-- 12, Reifel Bird Sanctuary, Delta
Feb. 11 and 12-- 8, Reifel Bird Sanctuary (one killed by a Merlin)
Feb. 11-- 13, Judson Lake (on the International Boundary near
Abbotsford, BC)
Feb. 13-- 1, Reifel Bird Sanctuary
Feb 8-- 3, Somenos Marsh, near Duncan, BC
Feb 8-- 5, Cowichan Bay, near Duncan, BC
Feb 26-- 1, Iona I., Richmond

Associated with the early February BARN SWALLOW influx were a few TREE
SWALLOWS, at least 2 weeks earlier than usual, as follows:

Feb 6-- 2, Cowichan Bay
Feb 8-- 2, Somenos Marsh and 1, Cowichan Bay

None of the above sightings were published in NORTH AMERICAN BIRDS,
because the B.C.-Yukon report for that winter was not received in time
for publication. The list of sightings is incomplete-- e,g., I am
aware of other sightings in the Chilliwack, BC area, for which I could
not find details in a quick search.

I did not do an exhaustive search for BARN SWALLOW records in WA and
OR for the 1999/2000 winter. However, the NORTH AMERICAN BIRDS report
(Mlodinow, Tice, and Tweit) lists BARN SWALLOW reports from 6
locations in western OR and 4 locations in western WA, mostly
involving single birds.

In the winter of 2000/2001, the only winter report of BARN SWALLOWS in
BC was 2 birds at the Westham I. bridge, Delta, on Feb. 2 and 3. (I
saw these birds, as well as one at the Reifel Sanctuary on Feb. 13,
2000.) The NORTH AMERICAN BIRDS report for winter 2000/2001 (Mlodinow
and Tweit) reported a total of 4 Barn Swallows in western OR and 9 in
western WA. (I presume this is the total number of birds, not the
number of localities.)

In other words, for the last 3 winters, there have been January and/or
February reports of BARN SWALLOWS in western Oregon, western
Washington, and southwestern BC each winter. Although it has been
normal for a few straggling BARN SWALLOWS to remain into December most
years near Vancouver, BC (mainly at one locality, the Reifel Bird
Sanctuary), the occurrence of this species in January and especially
February is a new phenomenon, which has become apparent only in the
last 5 years or so.

As for the "Pineapple Express" theory that I put forward for the
midwinter appearance of Barn Swallows in the Northwest, I agree that
this may not be the whole story. At least two people (Wayne Hoffmann
on OBOL and Ian Paulsen in a private posting) have pointed out that
"Pineapple Express" storms probably account, at best, for only part of
the northward movement of Barn Swallows. These storms come from the
southwest, from the general direction of Hawaii, and Barn Swallows
would likely have to already be in central or northern California
before they encountered suitable southerly winds. (Even though the
storms come from a SW direction, the local winds accompanying them are
often SE or S winds.) Barn Swallows are rare in winter even in S
California (as noted by Joel Geier on OBOL), so it seems possible that
swallows appearing in the Northwest in winter originate from somewhere
in Mexico-- perhaps travelling north by a combination of active and
passive movements.

Another flaw with the "Pineapple Express" theory is, why are there so
few TREE SWALLOWS and almost no VIOLET-GREEN SWALLOWS reported along
with BARN SWALLOWS, even though these two species winter much farther
north?

Nevertheless, I disagree with the ideas that (1) the BARN SWALLOWS
were present throughout the late fall and early winter at or near the
localities where they showed up in Jan. and Feb., and (2) this is some
kind of "early migration". I am convinced that weather patterns are at
least part of the explanation, especially when you consider the
simultaneous appearance of numerous BARN SWALLOWS at widespread
locations in early February 2000 and early to mid-January 2002.

I also disagree with Gene Hunn's suggestion that swallows could be
going into torpor and then re-emerging during periods of mild weather.
Torpor (a major reduction in body temperature and metabolic rate
during cold weather) has been well-documented in some hummingbirds,
caprimulgids (e.g. Poor-will) and swifts, but not, to my knowledge, in
passerines. (Were you serious, Gene, or were you pulling our legs??)

Migration in birds is generally under the control of hormones,
although the timing varies from species to species (e.g., TREE
SWALLOWS generally arrive about 6-7 weeks before BARN SWALLOWS).
Perhaps there are a few Barn Swallows with hormonal irregularities
that cause them to move northward many weeks earlier than usual?
An alternative explanation is that these movements are "weather
movements" which are independent of hormones or true migration.
"Hard-weather" movements, often in January or February, are
well-documented in waterfowl, where geese or ducks will move hundreds
of miles south in response to severe weather, long after migration
(and the hormonal stimulus for migration) has ceased. Maybe this is an
analogous "mild-weather movement"?

We certainly don't have any definitive answers to the "swallow
question", but many thanks to the numerous individuals that have
expressed their views on the subject, especially Steve Mlodinow,
Eugene Hunn, Ian Paulsen, Dave Irons, Wayne Hoffmann, Mike Patterson,
and Joel Geier. Let's continue to document winter swallow sightings,
and see if the patterns become clearer in a few years.

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