LATITUDINAL VARIATION IN BREEDING PARAMETERS OF THE COMMON KESTREL FALCO TINNUNCULUS

Abstract

SUMMARY.—Latitudinal variation in breeding parameters of the common kestrel Falco tinnunculus. We analyzed geographic variation in laying date, clutch size, and number of fledglings in the common kestrel Falco tinnunculus in the Western Palearctic. We also examined whether breeding parameters of some island-dwelling kestrels differed in latitude, with special reference to Tenerife Island. General Linear Models were applied. The mean laying date (LD, mean 30 April) correlated positively with latitude, with a delay of 6 days for every 10 oN. The mean clutch size (CS, mean 4.95 ± 0.26) increased significantly with latitude and was affected by nest-type (nest-box vs natural nests). The mean number of fledglings showed no correlation. Tenerife populations nesting below 1,000 m.a.s.l. showed the earliest LD in the Western Palearctic while those nesting above 1,000 m.a.s.l. showed a similar nesting pattern to European populations, although the CS is lower. The latitudinal variation in LD and CS coincides with the classical postulates (delay and increase respectively, towards the North) but does not explain the variations presented here. In agreement with recent studies, nest-type (nest-box vs natural nests) and climatic factors such as temperature (winter, spring) and spring rainfall influence latitudinal variations. Data from Tenerife are consistent with the hypotheses of delayed breeding associated with altitude and reduced CS in island birds.