Sexual Dimorphism as a Potential Driver of Trophic Specialisation in a Sedentary Synanthropic Bat Species

Intraspecific differences between the sexes can be as large as those between species, and niche partitioning between sexes may reduce competition for resources during energetically demanding periods. In bats, females are typically larger than males-a pattern attributed to greater reproductive investment (Big Mother hypothesis)-yet the functional implications of this dimorphism for foraging ecology remain poorly understood. We tested the hypothesis that sexual size dimorphism in cranial, wing and forearm morphology provides a functional basis for sex-specific foraging ecology in Cnephaeus (Eptesicus) serotinus, a European sedentary synanthropic species with pronounced spatial segregation between sexes during the breeding season. Using craniometric measurements (n = 137), wing morphometrics (n = 22) and forearm length from long-term monitoring (n = 1385) collected in northeastern Ukraine, we found consistent female-biased dimorphism across all traits. Females were significantly larger in forearm length (+3.2%; Cohen's d = 1.07), with this pattern stable across 12 years of monitoring and consistent between age classes. Wing surface areas showed the greatest dimorphism (14%-15%; d = 1.6-2.0), while wing shape indices did not differ, indicating isometric size scaling consistent with compensation for pregnancy-related mass increases. Mandibular dimensions related to bite force showed substantial dimorphism (2%-3%; d = 0.8-0.9), suggesting enhanced prey handling capacity in females. These findings are consistent with recent molecular dietary studies documenting sex-specific prey consumption in other bat species. Our results provide morphological support for the hypothesis that sexual dimorphism enables both flight performance during pregnancy and intraspecific trophic niche partitioning, potentially reducing intersexual competition during reproduction.