Behavioral response to conspecific songs on foraging territories of the heart-nosed bat

Abstract

Singing to create and defend territory boundaries is common among birds but rare in mammals. The African heart-nosed bat, Cardioderma cor, is hypothesized to use loud, low-frequency songs to reestablish foraging territories nightly. Territoriality can be defined ecologically, whereby an individual exclusively uses an area repeatedly, and behaviorally, through defense of an area. C. cor males sing on tightly abutting, exclusive areas nightly, which they return to throughout the season and sometimes across seasons. C. cor meets the ecological determinants of territoriality, but assessments of the use of song to maintain territories are lacking. We explore the singing behavior in this species by conducting song playback experiments within the borders of singing areas of 10 target individuals, with echolocation playbacks conducted as a control. In addition, we further explore the influence of song metrics on the behavioral response. Song playbacks prompted investigative and aggressive behavior, including passing by, approaching, and in one case, attacking the speaker, whereas echolocation did not. Additional post hoc analyses suggested that major song parameters, including song length, syllable frequency, intersyllable interval, and the number of double syllables comprising song stimuli influenced the level of response. For five bats we assessed whether their songs changed in response to the playback, and found that they sang faster, lower-frequency songs. These results are consistent with observations in other territorial animals including birds and gibbons, and provide a basis for further exploration of the territory defense hypothesis in the heart-nosed bat. We conclude that C. cor song features likely play an important role in mediating behavioral interactions within signaling networks of foraging bats.

Significance statement

It has been hypothesized that birdsong first evolved in support of territorial defense because it offered a cost-effective alternative to patrolling large spaces by flight. Singing-like behaviors have also been documented in several species of bats but never as a tool for maintaining foraging territories. However, evidence of foraging territoriality is scarce for bats, likely due to technical challenges associated with documenting such behaviors for a small, flying animal that may travel large distances at night. Here, we show for the first time that a bat responds to conspecific songs in a manner strikingly similar to many songbirds, providing support from outside songbirds for the hypothesis that territorial defense is a key selective pressure for singing in small, flying animals. This work provides the important basis for continuing to explore the role of singing, including song variability, in natural bat behavior outside of the roost.