Sex and Age Dimorphism in the Barn Owl and a Test of Mate Choice

Abstract

I investigated sex and age dimorphism and the possible effect of body size on mate choice in a northern Utah population of the Barn Owl (Tyto alba). In all characters measured (body mass; length of body, tarsus, foot, tail, and wing; and wing area), females averaged larger than males, but the ranges of these values overlapped considerably. Females were significantly larger than males in all characters except wing chord and tail length. Males had significantly lower wing loading than females. Lower wing loading could contribute to more efficient foraging by males and thus support hypotheses that partitioning of reproductive duties between the sexes may play an important role in reversed sexual dimorphism. Adults and immatures did not differ in size. I found no evidence to support the hypothesis that females choose small males as mates.