[Ontbirds]Snowy Owl Flight Year - Cause(s)
jeaniron at sympatico.ca
Wed Nov 26 13:46:52 EST 2008
Snowy Owls are being seen south of the Arctic in high numbers this
fall. Most of the early arriving owls have been first winter males
hatched last summer. Reports last summer indicated that lemming
numbers were high across the Eastern Canadian Arctic from Churchill,
Manitoba, to Bylot Island, Nunavut.
We previously reported that the cause of the Snowy Owl flight was a
lemming crash in the Eastern Arctic. However, we've had recent
correspondence indicating the cause of the flight was a very good
breeding season, which produced high numbers of young Snowy Owls.
Gilles Gauthier and his PhD student Jean-Francois Therrien of Laval
University in Quebec City report that based on "the high abundance of
lemmings we observed on Bylot Island and at all sites we visited on
Baffin Island last summer, we predicted that the abundance of Snowy
Owls should be very high this winter (in the south). Indeed, some
analyses made by Jean-Francois using the Christmas Bird Count data
showed a good correlation between the abundance of lemmings on Bylot
Island and the number of owls observed the following winter in Quebec
and Ontario for the period 1993 - 2007. So far, our prediction is
So was there also a lemming crash that is contributing to the Snowy
flight? Bruce Di Labio did environmental surveys on southern Baffin
Island in August and in central/southern Baffin in September and
October. He reports that very few lemmings were caught in live traps.
This might be an indication of a lemming decline in September and
October when most researchers were not in the Arctic. Lemmings
normally crash in fall and winter after a period of high abundance
and cycles are usually synchronous across the Eastern Arctic.
The Snowy Owl flight this fall and winter could be caused solely by
high numbers of young being fledged this summer due to high lemming
populations. Or is the flight the result of a good breeding year and
a subsequent decline in lemming numbers this fall? If a large number
of adult Snowy Owls come south this winter then we'll be more
confident in saying that a lemming crash has occurred. We'll post
updates as we get new information.
Baffin Island lies west of Greenland and is the largest island in the
Canadian Arctic. Bylot Island (lat 73 deg, long 78 deg) is about 3000
km (1865 mi) north of Toronto. Bylot is much smaller than Baffin. It
is at the northeastern tip of Baffin on Lancaster Sound "Northwest Passage".
Acknowledgements: We thank Ken Abraham, Bruce Di Labio, Bruce Falls,
Gilles Gauthier, Jean-Francois Therrien, and Michel Gosselin for
information and discussions about lemmings and Snowy Owls.
Ron Pittaway and Jean Iron
Toronto and Minden ON
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