> From: Jean Iron <[log in to unmask]>
> Date: November 26, 2008 1:46:52 PM EST (CA)
> To: [log in to unmask]
> Subject: [Ontbirds]Snowy Owl Flight Year - Cause(s)
> 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 nicely upheld."
> 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
> 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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