Cranial dimorphism in Eurasian red squirrels, Sciurus vulgaris from Slovakia

Skulls of the Eurasian red squirrel (Sciurus vulgaris) from samples originating from the eastern part of Slovakia and collected during the years 1956-1987 were studied using morphometric analysis. Twelve cranial variables were measured and evaluated on 75 skulls (42 males; 33 females) in regard to the sex of the animals. The overlap of the values of the measured traits in adult males and females was high, but in many traits females seems to exhibit slightly higher mean values. Nevertheless, these differences were non-significant, with the exception of mandible height. Similarly, the results of discriminant function analysis support there being no differences between the sexes. We discussed whether the habitat, biology, mating system and variation in skull and dental variables were connected to the lack of sexual size dimorphism (SSD) in the Eurasian red squirrel. We explained the non-significant results regarding SSD through the benefits of the same size for both sexes in the protection of territory as well as inter- and intra-sexual interaction. On the other hand, the slightly larger proportions of females may have an advantage during pregnancy and lactation of young. Our study also shows that, the older museum material stresses the importance of collecting large samples of specimens, even of such common species as the red squirrels, which are currently the subject of species conservation.