Greater spear nosed bats commute long distances alone, rest together, but forage apart

Abstract

Group foraging animals may change their spatial relationships in response to the resource landscape. The strength of social network ties across foraging groups could then reflect the energy balance of individual group members through their effect on foraging efficiency. To test this, we tracked individuals in three social groups of Phyllostomus hastatus (greater spear-nosed bats) in Bocas del Toro, Panama. Phyllostomus hastatus seasonally feed on balsa flowers, and group-specific social calls are hypothesized to coordinate social foraging. We found that bats commuted alone but then joined group members in small foraging patches with high densities of flowering balsas, approximately 25 km from their roost. Their estimated energy expenditure was not related to their proximity social network, and network strength did not predict foraging efficiency. Bats in the same foraging patch did not coordinate foraging movement, but close proximity among individuals increased resting bout duration and synchrony. Bats across all social groups used the same resting areas, potentially due to the resting site's physical characteristics, proximity to abundant food resources or predation avoidance. These results indicate that factors other than increased feeding efficiency may structure network relationship of group members while foraging.