The Role of Nest-Site Availability and Territorial Behaviour in Limiting the Breeding Density of Kestrels

Abstract

(1) During 1976-9 European kestrels, Falco tinnunculus, in an upland area of young conifer plantation in south Scotland bred mainly in disused crow Corvus corone nests, usually in small woods in the valleys, and fed largely on voles. (2) In every year there was an excess of usable nests in the area. Usable nests were clumped with several nests of different ages in each small wood. In general only one pair of kestrels bred in each wood, but in the good vole years of 1978 and 1979 some pairs nested within 250 m of one another in the same woods. (3) During the breeding season, kestrels defended parts of their range around the nest, but overlap of male ranges increased with increasing distance from the nest. Territory size varied considerably within years, and, on average, was larger in the poor vole year of 1977 than in the better year of 1978. (4) The erection of artificial nests, which were subsequently occupied by kestrels, showed that lack of suitable nest sites had previously prevented breeding in some parts of the area.