Tweeters,

My comments on an apparent scarcity of ROUGH-LEGGED HAWKS this fall
has prompted similar comments from a number of other observers,
especially in eastern Washington.

One factor to take into account is that the number of Rough-legs
wintering in southern BC and Washington from year to year is highly
variable, and perhaps cyclic. Christmas Bird Count totals from
southern BC show weak evidence of a 4-year cycle, with highs tending
to coincide with Snowy Owl flight years. Rough-legs are tundra
breeders, but are probably not as heavily dependent on the cyclic
lemming populations as Snowy Owls.

I looked at counts from Ladner in the Fraser Delta and Vernon in the
Okanagan Valley, which are two of the best counts in BC for
Rough-legged Hawks. For the 21-year period from 1981 to 2001
inclusive, Ladner averaged 30 Rough-legs, with a low of 2 (1999) and a
high of 72 (1984). Vernon averaged 28, with a low of 7 (1985) and a
high of 46 (1997). I would emphasize that the evidence for a 4-year
cycle is weak, because "high" years at Ladner often did not coincide
with those at Vernon.

Combined totals for the 2 counts ranged from a low of 30 (1998) to a
high of 91 (1988). The years of 1984 and 1988 seem to stand out as
obvious "flight years".

A couple of observers have suggested that the low numbers so far are
simply because of a delayed migration. That's possible; however, in
most years, significant numbers of Rough-legs have arrived in southern
B.C. and Washington by mid-October, and most of them have arrived by
November 10th. I suspect that the real reason is not just a delayed
movement, but low numbers overall. The Christmas Bird Counts will tell
the story.

As for Red-tails, I haven't noticed a shortage around here (Kamloops
area), and if there are shortages of Red-tails, they would likely have
a different explanation than low numbers of Rough-legs.

Thanks to all those who have contributed their comments, and please
keep reporting on buteo numbers!

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