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Duncan, J.R. 1992. Influence of prey abundance and snow cover on great gray owl breeding dispersal. Ph.D. Thesis, University of Manitoba. 127 pp.


The influence of prey abundance and snow cover on the breeding dispersal of radio-marked adult great gray owls, Strix nebulosa, was investigated from 1984-90 in southeastern Manitoba and adjacent Minnesota. Of 2,004 prey items identified, 84% were meadow voles, Microtus pennsylvanicus. A great gray owl breeding density index fluctuated synchronously with multi-annual prey population changes.

During increase and peak vole population phases, adult owls remained on their breeding home ranges and did not disperse. Breeding dispersal was independent of snow cover and occurred following prey population crashes. There was no difference between male and female mean dispersal azimuths (14 degrees versus 6 degrees, p=0.48) and these were non-random (p<0.01) and significantly directed (p<0.05). Evidence of post-dispersal breeding-site fidelity was observed. On average, adult females dispersed farther (372 versus 235 km, p<0.05) than adult males. A significant female-biased sex ratio was detected among winter-caught great gray owls (adults only, p<0.05).