Resting together, foraging apart: Network structure of foraging bats is not explained by energy expenditure or foraging efficiency

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 Colon, Panama, using high frequency GPS during a season when balsa had begun to flower. We found commuting distances of 20-30 km to foraging sites, more than double of what has been previously reported. 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 bat positively influenced time outside of the cave and increased the duration and synchrony of resting. These results suggest that social proximity seemed to be more important during resting, and indicate 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 may use social information only for current patch discovery. They then may no longer rely on social information during daily foraging. HighlightsO_LIUnlike in Trinidad, greater spear-nosed bats in Panama do not commute or forage as a group C_LIO_LIForaging distances are double of previously known and across the sea C_LIO_LIBats rest near each other, but do not forage more efficiently when close C_LIO_LISocial information may mainly be used for the discovery of feeding areas C_LIO_LILocal resource landscapes may cause strong variation in social behaviour C_LI