Barred Owl’s westward spread has made headline news recently. But in its early stages, the range expansion drew little notice.
Historically, Barred Owl was known to occur only as far west as the edge of the Great Plains. Its expansion across the sparsely populated northern parts of the Prairie Provinces of Canada was not documented in detail, mainly because observers were few. The species was found nesting in northern British Columbia by 1946, but farther east, the first nesting records for Saskatchewan were in 1961 and for Alberta in 1966.
We have more information on what happened as it spread toward southern and coastal British Columbia and south into the western United States. By 1965 it had been found in Washington, and it had spread to Oregon by 1974 and to California by 1981. It is now fairly common along the Pacific slope from southeastern Alaska to central California.
Why did the owl expand its range so far and so fast? The explanation given most often is that humans aided its spread across the northern prairies by planting trees and by suppressing fires. That doesn’t seem convincing; most Barred Owls in central Canada are in regions that have always been forested, and they’re still absent from open prairies of those provinces. Whatever the reason, large-scale changes in bird distribution do occur sometimes, not always as a result of human activity. — Kenn Kaufman, Contributing Editor
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A version of this article appeared in our December 2013 issue.