The high-output singing displays of a lekking bat encode information on body size and individual identity

A growing body of research suggests that songs are an important part of the courtship behavior of many bat species, however there is little information on the basic characteristics of these vocalizations, or how they may function as a courtship signal. Lekking male lesser short-tailed bats (Mystacina tuberculata) appear to use vocal displays as a primary method for attracting mates, but it is unclear if these vocalizations constitute songs, and what characteristics females may use for mate selection. We recorded 16 lekking males and described the frequency and temporal properties of their vocalizations. We identified four notes (upsweeps, downsweeps, trills, and tones) that comprise courtship vocalizations, and males produced these notes either singly, or combined them linearly to form composite syllables. We classified 51 distinct syllable types (with an average of 29 types per male), with four (trills, upsweep-trills, trill-downsweeps, and upsweep-trill-downsweeps) comprising 69% of all syllables produced. The duration of trill-downsweeps scaled negatively with forearm length (a proxy for body size in bats), and all four main syllable types showed evidence of individuality. Based on the behavioral characteristics and contexts of these courtship vocalizations, we posit that this behavior constitutes singing. Furthermore, M. tuberculata potentially has one of the highest sustained song outputs yet described. Our results suggest the singing displays of M. tuberculata are signals that provide useful, honest cues of male characteristics and identity to females, and are as complex as the songs of many passerines. Male courtship displays are predicted to honestly advertise aspects of male traits. Like many birds, some bat species produce songs to attract mates, but the characteristics of these songs are not well understood within the context of sexual selection. We demonstrate that the courtship vocalizations of Mystacina tuberculata - a species that likely relies on singing as its primary method of mate attraction - are a complex set of signals. Males have large syllable repertoires, encode four of their most-common syllables with individual signatures, and have one of the highest recorded song outputs for either birds or bats. Moreover, the length of one of the most commonly used syllable types is inversely related to male size, providing females the opportunity to appraise male size by auditory cues alone. Our work is part of a growing body of research demonstrating singing behavior in bats.