Acoustic communication and group cohesion in spix’s disc-winged bats

Abstract

Acoustic communication is an especially important means by which social and highly mobile organisms, such as bats, locate group members. Contact calls are known to be used by many species of bats, including those that use permanent roosting structures; these roosts may facilitate group cohesion because individuals can rely on spatial memory and fidelity to a roosting location to relocate group members. However, the neotropical insectivorous bat Thyroptera tricolor is known to form extremely cohesive social aggregations despite moving daily between roost-sites. This species uses developing tubular leaves of plants such as Heliconia species that unfurl in a few hours, rendering them unsuitable in less than 24 h. Our research shows that T. tricolor uses a combination of two social signals, “inquiry” and “response” calls, to locate each other during flight and while roosting. Individuals may recognize, and be able to preferentially associate with, group members due to strong individual signatures in these two types of calls; group cohesion may be further facilitated by recognition based on spatial location, as this species uses small roosting home ranges and exhibits extreme philopatry to the natal territory. Coupling spatial memory with acoustic communication may be an especially effective mechanism of recognition in this system, as tubular roosts cause significant distortion of acoustic signals used during contact calling. The tubular leaves, however, also provide a significant increase in signal amplitude that may allow bats to locate each other over longer distances. Our work with T. tricolor not only highlights the important role that social calls play in maintaining cohesive groups in highly mobile species, but the role that roosting structures may play in facilitating sociality in bats.