A test of male mating and hunting success in the kestrel: The advantages of smallness?

We tested female choice for male wing and tarsus length and body mass in the kestrel (Falco tinnunculus), a species in which males average about 10% smaller than females. We also studied how male characters are related to their hunting success. In the laboratory, females preferred lighter males with shorter tarsi as mates, if the difference in those characters between competing males was larger than average. Lighter and shorter-winged males seemed to be better hunters than heavier and longer-winged males. Field observations in a year in which voles were scarce suggested that shorter-winged males were also better food providers in courtship feeding than longer-winged males, although in good vole years such a relationship was not found. We argue that females may prefer to pair with smaller males, because they have higher flight performance and better hunting success than heavier males. By doing so, females may gain direct breeding advantages. We conclude that both female choosiness and the hunting efficiency of males well contribute to reversed sexual size dimorphism (RSD, females larger than males) in the kestrel.