Turnover, age and sex ratios of kestrels (Falco tinnunculus) in south Scotland



This paper examines the composition and turnover of a population of European kestrels Falco tinnunculus L. in the Southern Uplands of Scotland. Turnover was generally high, with most birds staying in the area for only one summer or winter. The rate at which birds arrived or left was highest in autumn and spring, and was independent of population size. During winter, breeding males were more likely to stay on their territories than females, and males that did so were more likely to retain their partners the following year. Breeding success was associated with a greater likelihood of return the following year, except in first-year females which were unlikely to return anyway. The sex ratio was biased toward males in winter, especially in poor vole years when there were also few first-year birds present. The study confirmed the high rate of turnover reported elsewhere in small raptors, and further indicated that the composition and turnover of the population were related to food supply and seasonal patterns of migration.