Sexing Mute Swans Cygnus olor by discriminant analysis

Abstract

External measurements taken readily in the field were used to develop an alternative method of sexing Mute Swans Cygnus olor. Measurements of weight, tarsus length and skull length were taken during the period 1982 to 1999 in an area of southeast Scotland, UK. A discriminant function was developed using these biometrics to distinguish between males and females. The function derived for cygnets exceeding 7 kg in weight successfully described the sex of 88% of the original data when tested by jack-knifing. A function derived for adults correctly assigned 95% of a novel data set. Factors other than sex may influence the size of animals in a population overall, and so application of these functions to discriminate data from a wider geographical area, and when applied by other fieldworkers, should be tested prior to use. © 2003 British Trust for Ornithology.