Sexual dimorphism of four owl species in South Africa

Sexual dimorphism was studied in four South African owl species (African Grass-Owl Tyto capensis, Barn Owl T. alba, Marsh Owl Asio capensis and Spotted Eagle-Owl Bubo africanus) by examining specimens of intact owl carcasses found killed by vehicles along a national road in Gauteng province, South Africa. Females were significantly heavier and larger than males for most species. The body mass and length of T. capensis, and body mass and tail length of A. capensis, were significantly different, with females being larger than males. Body, wing, tail and tarsus length for T. alba males were significantly different to females. For B. africanus, only tarsus length was found to be significantly different among genders. These findings were reiterated further when applying a dimorphism index to the same morphometric measurements. This study contributes to morphometrics distinguishing the sexes of the four southern African owl species, especially T. capensis, which has a Vulnerable IUCN status.