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VTBIRD  November 2008

VTBIRD November 2008

Subject:

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

From:

Eve Ticknor <[log in to unmask]>

Reply-To:

Vermont Birds <[log in to unmask]>

Date:

Wed, 26 Nov 2008 18:04:58 -0500

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (77 lines)

FYI

> 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  
> 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
>
> _______________________________________________
> ONTBIRDS is presented by the Ontario Field Ornithologists - the  
> provincial birding organization.
> Send bird reports to ONTBIRDS mailing list [log in to unmask]
> For instructions to join or leave ONTBIRDS visit http://www.ofo.ca/ 
> information/ontbirdssetup.php
> ONTBIRDS Guidelines may be viewed at http://www.ofo.ca/information/ 
> ontbirdsguide.php
>

Eve Ticknor
Coordinator OFNC Falcon Watch
38-9 Gillespie Cres
Ottawa, Ontario  K1V 9T5
613-859-9545

"All nature is but art, unknown to thee"

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