Sexing Eurasian Eagle Owls by external body and skeletal measurements

Abstract

The aim of this study was to obtain an effective tool for sex determination in Eurasian Eagle Owls (<em>Bubo bubo</em>), a species without marked sexual dimorphism, by taking external body and bone measurements. Thirty-one individuals were used for this purpose, 16 males and 15 females, and 42 measurements were obtained: 19 external and 23 bone measurements. Three discriminant analyses were carried out: the first with external measurements only, a second one with bone measurements only, and a third combining both. The validation of the classification was performed by cross-validation. The first analysis led to a discrimination function with five external measures, with a Wilk’s Lambda of 0.064 and 100% of the individuals classified correctly. The second analysis led to a discrimination function with two bone measures, with a Wilk’s Lambda of 0.282 and 90% of individuals correctly classified. The third analysis led to a discrimination function with six external and two bone measures, with a Wilk’s Lambda of 0.022 and 100% of individuals classified correctly. The study has shown that external measurements are more efficient than bone measurements, and likely sufficient for sexing. Nevertheless, bone measurements can provide complementary information, although alone they are insufficient for sexing owls, given that the length of the ulna and the nose bones were the only useful bone measurements. It can be generalized that this work provides an optimal sexing method, useful in ornithological ecology, clinical and forensic medicine, as well as in archaeozoological studies.