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

Abstract

Animals frequently forage in groups on ephemeral resources to profit from social information and increased efficiency. Greater spear-nosed bats, Phyllostomus hastatus, develop group-specific social calls, which are hypothesized to coordinate social foraging to feed on patchily distributed balsa flowers. To test this, we tagged all members of three social groups of P. hastatus on Isla Colón, Panamá, using high-frequency GPS during a season when balsa had begun to flower. We found that bats commuted 20–30 km to foraging sites, more than double the distance reported previously. In contrast to our expectations, we found that tagged individuals did not commute together, but did join group members in small foraging patches with high densities of flowering balsas on the mainland. We hypothesized that close proximity to group members would increase foraging efficiency if social foraging were used to find flower clusters, but distance between tagged individuals did not predict foraging efficiency or energy expenditure. However, decreased distance among tagged bats positively influenced the time spent outside roosing caves and increased the duration and synchrony of resting. These results suggest that social proximity appears to be more important during resting and that factors other than increased feeding efficiency may structure social relationships of group members while foraging. It appears that, depending on the local resource landscape, these bats have an excellent map even of distant resources and that they use social information only for current patch discovery, and thus, they do not appear to rely on social information during daily foraging.