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SummaryWe examined population and ecosystem patterns hoping to inform conservation strategies for Burrowing OwlsSpeotyto cuniculariain Canada. The owls chose moderately to heavily grazed grasslands for nesting and roosting, and avoided cultivated fields. Where grassland patches were isolated in 90% cultivation, owls dispersed later, for shorter distances and less often. Mortality rate during the 5-month study was high (adult ratio 0.45, juveniles 0.55), which may contribute to local declines. Additional mortality may occur on migration and during winter. We extrapolate from local effects (loss of grassland habitat with burrows for roosting, and ~2% “incidental” predation) to suggest that such changes detrimental to the owls occur throughout the central Great Plains ecosystem which the owls occupy year-round. The changes include ecosystem processes such as plant succession, owl dispersal and predation. These changes are likely to be irreversible on a scale that would be required to help this owl. The species may face extinction in Canada, at the northern limit of its range.

Raptors are an important component of pralrle ecosystems. I examined the effects of grassland conversion to agricultural fields on densltles of nest@ prairie hawks. Densltles of Swalnson's hawks were recorded for comparison. The 2 species of congenerlc hawks responded differently to habitat loss despite considerable overlap ln their use of resources. As cultivation on study plots increased, ferruglnous hawks declined. Swalnson's hawks were more abundant ln areas of moderate cultivation than ln grassland or in areas of extensive cultivation. Differences ln the hawks' responses were attributed to differences in their ecology, primarily prey utilization. There was no evidence that soil quallty affected hawk abundance.

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