Use of forest canopy by European red squirrelsSciurus vulgaris in Northern Greece: claws and the small branch niche

Moving and standing in trees impose multiple problems to arboreal mammals. Among them, the major ones are the negotiation of slender terminal branches and of large vertical supports. Both microhabitats are important as they have been linked alternatively to the evolutionary loss of claws in early primates. Therefore, rates of use of these different supports by claw-bearing arboreal mammals may offer insights to their actual significance in the adaptive evolution of early primates. In this context, canopy, tree crown, branch size, inclination, and texture use were recorded on four adult free ranging European red squirrelsSciurus vulgaris Linnaeus, 1758 in a mixed coniferous forest in northern Greece.S. vulgaris was mainly arboreal, exploiting the terminal branch zone, using frequently oblique and intermediately textured supports<5 cm and moderately large vertical branches. Furthermore, comparative data from other sciurid species and clawed primates showed positive correlations of small and horizontal support use, and negative ones of vertical support use to body mass. These findings show that keeled functional claws do not impede habitual use of slender branches and may not facilitate efficient climbing on large vertical trunks. These observations partly question the association between habitual use of the small branch niche and primate adaptations and lend support to alternative hypotheses, underscoring the importance of inquiring for more complex mechanisms that lead to the evolution of the unique set of primate morphological adaptations.