Habitat occupancy and regulation of clutch size in the European KestrelFalco tinnunculus

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Abstract
The population of European kestrels F. tinnunculus breeding in Britain [UK] increased 5-fold between 1963 and 1978. The diversity of nesting habitats used by the species quadrupled over the same time period. Moorland and inland cliff nesting grounds became relatively less frequent; agricultural and coniferous woodland became relatively more frequent. The breeding season was retarded in years of high population increase and accelerated in years of population decrease, possibly because of greater competition for territory in years of increase. Delay in breeding results in reduction of clutch size. The shift of breeding into a greater number of habitats is correlated with reduction in clutch size, as predicted from Brown''s (1969) theory of territorial regulation of populations.