A review of possible explanations for reverse size dimorphism of American woodcock

Abstract

Female American woodcock (Scolopax minor) exceed males in body size. The degree of dimorphism in American woodcock is greater than in many other shorebird species and is comparable to that in many accipiter hawks and owls. We examine three hypotheses that have been used to explain dimorphism for other avian species: that dimorphism enhances niche utilization by reducing intersexual competition for food, that large female size improves reproductive effort, and that males are small because of selection for agile display flights. Evidence is lacking, weak, or contradictory that any one of these three general hypotheses sufficiently explains reverse dimorphism in American woodcock. Despite our objections to the hypotheses, we point out needed research to elucidate better their ability to explain dimorphism. We speculate that selection pressure on males for early arrival and acquisition of territories also influences their small size.