Calling to the collective: contact calling rates within groups of disc-winged bats do not vary by kinship or association.

Many group-living animals coordinate social behaviours using contact calls, which can be produced for all group members or targeted at specific individuals. In the disc-winged bat, Thyroptera tricolor, group members use 'inquiry' and 'response' calls to coordinate daily movements into new roosts (furled leaves). Rates of both calls show consistent among-individual variation, but causes of within-individual variation remain unknown. Here, we tested whether disc-winged bats produce more contact calls towards group members with higher kinship or association. In 446 experimental trials, we recorded 139 random within-group pairs of one flying bat (producing inquiry calls for roost searching) and one roosting bat (producing response calls for roost advertising). Using generalized linear mixed-effect models (GLMM), we assessed how response and inquiry calling rates varied by sender, receiver, genetic kinship and co-roosting association rate. Calling rates varied consistently across senders but not by receiver. Response calling was influenced by inquiry calling rates, but neither calling rate was higher when the interacting pair had higher kinship or association. Rather than dyadic calling rates indicating within-group relationships, our findings are consistent with the hypothesis that bats produce contact calls to maintain contact with any or all individuals within a group while collectively searching for a new roost site. This article is part of the theme issue 'The power of sound: unravelling how acoustic communication shapes group dynamics'.

Landing manoeuvres predict roost-site preferences in bats.

Roosts are vital for the survival of many species, and how individuals choose one site over another is affected by various factors. In bats, for example, species may use stiff roosts such as caves or compliant ones such as leaves; each type requires not only specific morphological adaptations but also different landing manoeuvres. Selecting a suitable roost within those broad categories may increase landing performance, reducing accidents and decreasing exposure time to predators. We addressed whether bats select specific roost sites based on the availability of a suitable landing surface, which could increase landing performance. Our study focused on Spix's disc-winged bats (Thyroptera tricolor), a species known to roost within developing tubular leaves. As previous studies show that this species relies on the leaves' apex for safe landing and rapid post-landing settlement, we predicted that bats would prefer to roost in tubular structures with a longer apex and that landing would be consistently more effective on those leaves. Field observations showed that T. tricolor predominantly used two species for roosting, Heliconia imbricata and Calathea lutea, but they preferred roosting in the former. The main difference between these two plant species was the length of the leaf's apex (longer in H. imbricata). Experiments in a flight cage also showed that bats used more consistent approach and landing tactics when accessing leaves with a longer apex. Our results suggest that landing mechanics may strongly influence resource selection, especially when complex manoeuvres are needed to acquire those resources.