The Home Range and Density of Kestrels in Relation to Vole Abundance

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Abstract
Numbers of voles and kestrels, and kestrel home range, were measured over 3 yr in an upland area of a young conifer plantation in southern Scotland [UK]. Home ranges were assessed by spot observation of wing-tagged individuals and the results checked using radio tracking. The data were corrected to remove sample-size bias on the range size index, and because estimates were less accurate the larger the range. Kestrel numbers were high in autumn, declined during winter and rose again in spring. Kestrel numbers were positively correlated with vole abundance outside the breeding season and were higher, at any given vole density, in summer than in winter. Home ranges were used by individuals in winter but by pairs in summer. In winter there was little range overlap and kestrels defended most of their range. In summer only an area around the nest was defended, the rest of the range being shared with other pairs. Log range size was inversely correlated with vole abundance, values for the breeding season lying on the same trend as those at other times of year. Territory size appeared to be proximately determined by competition, rather than being directly related to food supply.

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