The Use of Culmen Length to Determine Sex of the American White Pelican

Abstract Culmen length has been suggested as being diagnostic for sex in the American White Pelicans (Pelecanus erythrorhynchos). However, the literature on the use of culmen length to determine sex is inconsistent, with reported overlap in culmen lengths for males and females ranging from 1 mm to >120 mm. Morphological measurements from 188 American White Pelicans collected in Mississippi and Louisiana whose sex was determined by dissection and gonadal inspection were measured. The use of culmen length alone was used to determine gender for this sample by establishing the minimum observed culmen length for males and the maximum observed culmen length for females that provided the fewest incorrect determinations for each gender. A multivariate discriminant function model was developed to determine sex from our data and compared the diagnostic accuracy of the model with the accuracy based on culmen length alone. Both methods were validated using an independently collected sample of 22 pelicans from Florida. A culmen length of ≥310 mm for males and ≤309 mm for females from our data correctly classified sex for 99% of American White Pelicans from our Mississippi and Louisiana samples and 95% of AWPE for the Florida sample. Culmen length and wingcord length were significant variables in the discriminant function model. The resulting model correctly classified sex of 97% of the birds and 94% of the independent Florida sample. The culmen length alone predicted the sex of American White Pelicans as well as multivariate methods and provides an accurate simple, non-lethal method for sexing the species.