Sexual dimorphism in cranial size and shape among red foxes Vulpes vulpes from north-east Ireland

Sexual dimorphism in cranial form was investigated for a sample of 204 adult red foxes Vulpes vulpes from north-east Ireland. Using a combination of principal component analysis and discriminant function analysis, size variation and allometry was found to account for 65.29% of the between-sex variation. The crania of male foxes were larger, more elongate and had a relatively narrower post-orbital constriction than those of the female of the species. A set of discriminant functions allowed sexing of unsexed material with over 86% accuracy. Discriminant functions derived from English and Welsh fox populations were found to sex Irish foxes with 78.4% and 85.8% accuracy, thus indicating that discriminant functions may not be entirely population-specific. These findings were discussed in the light of other studies of dimorphism in the species and on the 'adaptive' nature of such shape variation in carnivores.