Differences in the diets of resident and non-resident Kestrels in Spain

Abstract

The Eurasian Kestrel (Falco tinnunculus) is a partial migrant in Spain, i .e . some individuals migrate in autumn, while other ones are sedentary. In this paper the diets of resident and non-resident kestrels were compared during autumn to study whether differences in the diet may account for individual migratory behaviour. Results indicated that kestrels changed their feeding habits during autumn. Resident kestrels substituted grasshoppers, a typical summer prey, for field crickets and/or mammals (typical winter prey), whereas non resident kestrels hunted fewer crickets and mammals, but more mantids and flying ants, which are not available later, during winter . Trophic diversity (H') was larger for non-resident kestrels than for residents, which indicates that profitable substitution prey might be scarce in the territories of nonresident kestrels . Indeed, BPP (Biomass per whole pellet), which may be an indicator of daily energy intake, was lower for non-resident than for resident kestrels . The negative relationship between the date of disappearance and H' on one hand, and the positive relationship between date of departure to BPPfor non-resident kestrels on the other, indicates that these kestrels remained at the breeding sites for as long as possible .