Behavioural strategies associated with using an ephemeral roosting resource in Spix's disc-winged bat

Abstract

The limited availability of refuges may represent an important factor promoting the evolution of sociality, particularly in bats. Spix's disc-winged bats (Thyroptera tricolor) show highly specialized morphological adaptations that enable individuals to roost inside furled musoid leaves. This roosting ecology presents major challenges, as leaves rapidly unfurl, forcing bats to locate new roosts on a daily basis. Despite the reliance of T. tricolor on such ephemeral roosting resources, bats form stable group associations. This social stability has been attributed to the potential benefits that group members gain from searching for new roosts together versus alone. The purpose of our study was to characterize the behavioural patterns associated with assessing roosts and any accompanying communication strategies of Spix's disc-winged bat. We determined that bats regularly monitor furled leaves within their roosting range, during which they emit a number of distinct social calls. Roost assessment involved close inspection of leaf dimensions and surroundings, and was mostly performed by single individuals. Thyroptera tricolor's call repertoire during flight indicates that group contact involves a combination of acoustic signals. Our approach in a natural setting provides valuable insight into the role of shelter stability in the evolution of the T. tricolor social system.

Social communication in bats

“…Contact calls represent a particular type of social call directed primarily towards roost mates; to facilitate recognition, social calls encode individual or group ‘signatures’. For example, in pallid bats ( Antrozous pallidus ), vampire bats, and Spix's disc‐winged bats ( Thyroptera tricolor ), social calls have individual signatures (Fenton et al, ; Arnold & Wilkinson, ; Carter et al, ; Gillam & Chaverri, ) which allow bats to discriminate, and preferentially join, group members within roosts but also during flight (Chaverri et al, ; Montero & Gillam, ). Contact calls may be additionally used to retrieve group mates before foraging (Boughman & Wilkinson, ).…”

“…Both signals have signatures that allow bats to discriminate, and preferentially join, members of their own group (Gillam & Chaverri, 2012;Chaverri et al, 2013). This call-and-response system has only been recorded during the day and in this single context (Montero & Gillam, 2015), suggesting that the main function of this exchange of acoustic signals is the active recruitment of roost companions.…”

Type of shelter and first description of the echolocation call of disk-winged bat (Thyroptera devivoi)

“…Though, it is interesting to call the attention that T. devivoi from Jalapão was collected in a "vereda" rich in Heliconia (Gregorin et al 2006) while we found the species in dead leaves. As with most of the available information about the family, little is known about the acoustic biology of Thyropteridae, and that which exists mainly refers to two species (T. discifera and T. tricolor), with some studies focused on social calls (Chaverri et al 2010, 2013, 2015, Montero & Gillam 2015, while others concentrated on echolocation calls (Fenton et al 1999, Tschapka et al 2000, Barataud et al 2013, Rivera-Parra and Burneo 2013. Echolocation calls of T. devivoi recorded by us are of low intensity, which make them difficult to detect (Fenton et al 1999, Dechmann et al 2006.…”

“…This allows the bats to obtain high-quality detailed information on their surroundings (Schnitzler and Kalko 2001). We recorded a social call similar to that described by Montero and Gillam (2015) for T. tricolor, who qualified it as SQCF (short quasi-constant frequency). We do not know the purpose of this call for T. devivoi, but it is present during certain times of the night between periods of echolocation and, therefore, may possibly be emitted in flight.…”

“…The most common and well known are Thyroptera discifera (Lichtenstein & Peters 1854) and T. tricolor Spix 1823. Both species are distributed from Central America to south-eastern South America (Findley & Wilson 1974, Tschapka et al 2000, Vonhof & Fenton 2004, Dechmann et al 2006, Gillam & Chaverri 2012, Buchalski et al 2014, Montero & Gillam 2015. The other species are Thyroptera lavali Pine et al 1993, an Amazonian species occurring in northern South America (Solari et al 2004), and the recently described Thyroptera wynneae Velazco et al (2014), known only by four specimens collected in the forests of Peru and southeastern Brazil (Hoppe et al 2014, Velazco et al 2014.…”