Sunday, February 19, 2012

Snowy Owl

This winter witnessed one of the largest Snowy Owl invasions in recent memory. But seeing a Snowy took a whimsical road trip to Dodge County, Minnesota, on 17 February 2012 (thanks to a MOU listserv posting by Ken Vail), and eagle-eyed Erika to spot one. Snowy Owls prefer open country. Be wary of reports of Snowy Owls from forests--these owls may well be pale Canadian Great Horned Owls. I have seen Snowy Owls perch in small trees, but they prefer telephone poles or, like the one we found, on the ground in open fields.

The epicenter of this season's invasion seems to be the eastern Dakotas, but owls are also being reported from elsewhere in the Midwest (where they have reached Texas), the Pacific Northwest, and the northern Atlantic Coast (south to New Jersey and Pennsylvania). One Snowy Owl even made it to Hawaii! (Most of the data and the quote in this post are from an eBird article, interesting reading for anyone.)

When Erika and I lived in South Dakota, we could find a few Snowy Owls most winters. But larger invasions occurred more or less on seven-year cycles. Snowy Owl populations are dependent on Arctic lemmings. If a Snowy Owl does not see a lemming, the female does not even ovulate! Last summer was probably very productive for Snowy Owls in their Arctic breeding grounds. Lemming populations must have subsequently crashed, driving the owls south. The eBird folks speculate that, given the areas of winter concentration, "the source for these birds was presumably the central Arctic, or central-western Arctic. But without data from the breeding grounds, this connection is hard to make and even harder to prove." Few, if any, owls reaching the United States survive to return to their breeding grounds. Winter food sources are scarce here. Most owls are emaciated. The owls also suffer collisions with our abundant cars and power-lines. With fewer owls in the Arctic next season, lemming populations will rebound, and the cycle will renew.

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