Ardea
Official journal of the Netherlands Ornithologists' Union

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Duncan J.R., Swengel S.R. & Swengel A.B. (2009) Correlations of Northern Saw-whet Owl Aegolius acadicus calling indices from surveys in southern Wisconsin, USA with owl and small mammal surveys in Manitoba, Canada, 19862006. ARDEA 97 (4): 489-496
The Northern Saw-whet Owl Aegolius acadicus (NSWO) can be found year-round on its North American breeding range, but considerable numbers migrate south in autumn, with banding data documenting migration movements over 1000 km. Although the timing and routes of migration are better known in eastern North America, there is some evidence of a general movement from Manitoba, Ontario and Minnesota around Lake Superior to Wisconsin, and then south and/or east. We examined NSWO calling indices from annual auditory surveys in Manitoba, Canada (19912006) and from another study site over 770 km southeast in Wisconsin, USA (19862007) for covariance as evidence of a spring migration in central North America. In Manitoba and Wisconsin, NSWO calling showed a consistent pattern of regular periodicity, with peak calling every 27 years (average 35). Likewise, NSWO prey (small mammal) abundance in southeastern Manitoba surveys (19862006) showed a periodicity of 27 years. NSWO calling, both in Manitoba and Wisconsin, covaried significantly with small mammal abundance in southeastern Manitoba. NSWO indices in Manitoba covaried nearly significantly with the same year in Wisconsin, and significantly with the lag year in Wisconsin suggesting a spring migration takes place in central North America that is influenced by prey availability. This study highlights the need for more extensive analyses of long-term data from owl and prey surveys and for spring owl migration banding to better understand NSWO migration in North America.


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