© Museum and Institute of Zoology PAS. As a strategy to reserve energy for parental care, females are larger than males in most bat species. Although females are responsible for providing parental care in almost all (if not all) bats, there are some species in which the males are larger than the females, and in other species the sexes are similarly sized. It has been proposed that for non dimorphic bat species, some foraging traits might be responsible for the differences observed between the sexes, though, this hypothesis has not been tested formally. Here, we evaluate the sexual size dimorphism of the phyllostomid insectivorous bat Gardnerycteris crenulatum using the morphometric variables of body size and nose-leaf size; the latter is a functional structure that plays an important role in echolocation and determines insectivorous bats' effectiveness in foraging. Our results show that G. crenulatum is a sexually monomorphic species in terms of body size, but it is dimorphic in nose-leaf traits. Females exhibit larger nose-leaves than males, which could increase the directionality of their ultrasound emission and hence improve the females' ability to obtain sensory information. We propose that monomorphic bats could be dimorphic for functional structures related to foraging behaviour as a means to increase their energetic effectiveness.