Selection for reduced male size in raptorial birds: the possible roles of female choice and mate guarding.

Based on the assumptions that smaller prey is more abundant than larger prey and that smaller raptors capture prey more frequently than larger ones, the author presents 3 hypothetical mechanisms which would increase the fitness of small males: 1) sexual selection for indications of hunting proficiency as assessed by the female during courtship, such as the ability to produce food on demand and manoeuverability during displays, may incidently select for decreased male size; 2) more frequent courtship feeding may more effectively stimulate reproductive synchrony and copulatory receptiveness in the female, thus smaller males would be more successful in breeding; 3) smaller males might encounter optimally sized (most successfully pursued) prey with less searching time, allowing them to remain closer to the nest for more efficient guarding against other males and predators. Unlike previous theories, these mechanisms would have their principal effect during pairing and egg fertilization.-from Author