Some Observations and Comments on the Periodic Invasions of Goshawks

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Abstract
Observations of hawk migration near Cedar Grove, Wisconsin, in the autumns of 1950 through 1964 revealed an invasion of Goshawks in the years 1961 through 1963. The invasion was preceded by decreases in populations of snowshoe hare and Ruffed Grouse in central Canada and the upper Great Lakes area. Most of the invading birds were hatched in 1961. We hypothesize that older, established birds displaced younger, poorly established birds from a range that could not support large wintering populations of Goshawks.

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