Sexing Laughing Gulls Using External Measurements and Discriminant Analysis

Gulls are sexually dimorphic in size but are not distinguishable on the basis of a single mensural character. Laughing Gull adults (n = 165) from Tampa Bay, Florida, were measured to determine gonys depth, culmen length, total head length, tarsus length, tail length, wing length, and weight. Discriminant analysis identified total head length and gonys depth as the two most discriminating characters for identification of sex. The derived classification function was 95.1% accurate in assigning sex to individual birds and was 95.3% accurate in identifying the sex of an independent test sample of birds. The authors pooled the samples to derive a new function for use in the field. Classification scores may provide additional information about individual birds.