[Ontbirds]Snowy Owl Flight Year - Cause(s)

Jean Iron 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 
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 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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