The following was sent to me by Myke Chutter, Bird Specialist with the
Ministry of Environment, Lands and Parks, Victoria, B.C. It gives a
recent Canadian perspective of the species. A good note, so I've taken the
liberty to pass it on to Tweeters.

BRG
__________________

Further to all the discussion being sent via e-mail, I came across
the Winter 1994/95 issue of Bird Trends that was devoted to raptors. In an
article entitled "Raptor population status and trends in Canada" by D.A.
Kirk was the following reference to Swainson's Hawks:

"BBS data from the prairies ecoregion suggest a longterm increase in SWHA
populations, but recent declines in productivity in Sask and Alta are a
cause for concern. An overall analysis of migration counts in western N.
Amer. showed no significant trends, although a decline at a New Mexico site
from 1987-1990 was almost significant. Until relativley recently, western
raptors were not thought to follow leading lines (topographic features such
as mouintain ridges and coastlines) as do eastern raptors, but there have
been several discoveries of flyways through mountain passes or along ridges
in western N. Amer."

The article goes on to estimate the current # of breeding pairs in Canada at
20,000 - 50,000 pairs, but presents no BC data. In summary it includes the
SWHA as one of three species of diurnal raptor (out of 21 for which
population trends are best known) for which possible evidence of decline
exists.

Further on in the issue is another article by Kirk entitled "Productivity
declines in Swainson's Hawks and their significance to population trends"
which gives more details regarding this species (mostly in Alta,Sask and
Man), but again lacks any BC info other than a reference that includes
southern interior BC as part of their breeding range. In it he states:

"Their ecological niche was once the Great Plains, where bisons roamed,
frequent fires checked tree growth, and groundsquirrels and grasshoppers
were numerous (Houston 1990). Until recently, Swainson's Hawk populations
were apparently thriving. But new evidence suggests that SWHA may have
declined in Canada as they have in several western states"

Again he bases this on a marked decline in productivity during a 1987-1993
study even though BBS trends were stable. He states that these declines in
productivity are a cause for concern as "...Firstly, although numerous
factors have been proposed to account for the declines, the specific causes
have not been identified. Secondly, SWHA is one of the most abundant
raptors in the prairies and populations of other 'common' raptors are also
declining in the prairie ecoregion, despite the fact that they have a
different prey base.....This suggests that whatever is affecting populations
of these species is pervasive and large-scale"

Just thought I'd pass this along.

Cheers, Myke
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Bryan Gates, Victoria bgates at assessment.env.gov.bc.ca