Abstract
We used a 13-year time series of abundance estimates of breeding Northern Saw-whet Owls (Aegolius acadicus), and of small mammals from central Ontario, Canada, to assess the numerical response of the owls to small-mammal prey species. We found that the finite rate of increase of breeding owls was directly related to estimates of red-backed vole (Myodes gapperi) abundance. Thus, it appeared that the owls were nomadic, and made decisions about where to breed based on vole supply. The owls showed a much weaker response to deer mouse (Peromyscus maniculatus) abundance. Across all years, 55% of variation in owl rate of increase could be uniquely attributed to vole abundance, whereas only 3% could be attributed to mouse abundance. Consistent with the model of nomadism, there was only a weak relationship between the proportion of hatch-year owls caught at fall banding stations, and small-mammal abundance. Instead, it appeared that Northern Saw-whet Owls avoided years of widespread reproductive failure through the nomadic strategy of selecting breeding sites based on vole supply.
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Acknowledgments
Funding for this work was provided by the Ontario Ministry of Natural Resources, Bird Studies Canada, Long Point Bird Observatory, the University of Guelph, and the Natural Sciences and Engineering Research Council of Canada. We thank the many technicians and the volunteer owl surveyors and banders who to helped collect the data. Jeff Marks and Matt Reudink provided helpful comments on the work.
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Communicated by F. Bairlein.
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Bowman, J., Badzinski, D.S. & Brooks, R.J. The numerical response of breeding Northern Saw-whet Owls Aegolius acadicus suggests nomadism. J Ornithol 151, 499–506 (2010). https://doi.org/10.1007/s10336-009-0482-3
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DOI: https://doi.org/10.1007/s10336-009-0482-3