A new method for sexing Oriental White Storks

ABSTRACT.   For species where males and females are monomorphic, or nearly so, determining the sex of individual birds generally requires either capturing birds or collecting samples, such as feathers, for DNA analysis. We developed a new method, involving the use of photographs, to determine the sex of endangered Oriental White Storks ( Ciconia boyciana ). Using photographs, we analyzed the lateral features of the heads of 25 captive storks of known sex (12 males and 13 females) and found differences between males and females in the distance from the bill tip to the nape and the distance from the bill tip to the commissural point. These differences were used to generate a discriminant function that was then tested on 22 captive storks at Hyogo Homeland Park (Toyooka, Japan), and we correctly determined the sex of 18 individuals (82%). In addition, the sex of two wild storks was correctly assigned. Our results suggest that good-quality photographs can be useful for determining the sex of both captive and wild Oriental White Storks and, further, that similar methods may prove useful for determining sex in other species of birds.