Mixed-species groups in bats: non-random roost associations and roost selection in neotropical understory bats

Background: Mixed-species groups in animals have been shown to confer antipredator, foraging and other benefts to their members that may provide selective advantages. In most cases, however, it is unclear whether functional benefts are a principal driver of heterospecifc groups, or whether groups simply result from simultaneous exploitation of common resources. Mixed-species groups that form independently of environmental conditions may, however, evidence direct benefts of species associations. Bats are among the most gregarious mammals, with sometimes thousands of individuals of various species roosting communally. Despite numerous potential functional benefts of such mixed-species roosting groups, interspecifc attraction has never been shown. To explore alternative explanations for mixed-species roosting, we studied roost selection in a speciose neotropical understory bat community in lowland rainforest in Costa Rica. Long term roost data were recorded over 10 years in a total of 133 roosts comprising both natural roosts and structurally uniform artifcial roosts. We modelled bat roost occupancy and abundance in each roost type and in forest and pasture habitats to quantify the efects of roost- and environmental variability. Results: We found that bat species presence in natural roosts is predictable from habitat and structural roost parameters, but that the presence and abundance of other bat species further modifes roost choice. One third of the 12 study species were found to actively associate with selected other bat species in roosts (e.g. Glossophaga commissarisi with Carollia sowelli). Other species did not engage in communal roosting, which in some cases indicates a role for negative interspecifc interactions, such as roost competition. Conclusions: Mixed-species roosting may provide thermoregulatory benefts, reduce intraspecifc competition and promote interspecifc information transfer, and hence some heterospecifc associations may be selected for in bats. Overall, our study contributes to an improved understanding of the array of factors that shape diverse tropical bat communities and drive the dynamics of heterospecifc grouping in mammals more generally