The usual explanation for irruptive years is a BIG food year (lots of lemmings) with a lot of productivity in the Snowy Owls (lots of young owls) then those inexperienced young disperse looking for feeding area for the winter. Competition forces them south. Lemmings do have a chaotic population distribution (boom or bust) so it seems "reasonable"/

A very good FAQ ... with links to papers too.

http://home.pacifier.com/~neawanna/SNOW/SNOW_FAQ.html

As the Capitol Hill Snowy showed they're quite catholic eaters.

Previously posted to TWEETERS by Mike Patterson (they don't believe the lemming fluctuation story)

http://mailman1.u.washington.edu/pipermail/tweeters/2005-December/045508.html

I'm not sure what the typical mortality is for Snowy Owls but for Cooper's Hawks (and other obligate predators) the first year mortality is 50% or so. They either get good at catching dinner or they starve. Being a predator is not a happy life.

On Nov 13, 2012, at 10:08 PM, Wendy Thuring wrote:

> I am wondering if there is something more going on with their habitat or the lack of food that has sent them south now two years in a row. Are these warning signs, or am I worrying over nothing?

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Kevin Purcell (Capitol Hill, Seattle, WA)
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