Adaptive adjustment of the FM component of calls in CF-FM bats is not involved in avoidance of conspecific jamming

Abstract

Echolocating bats observe their surroundings through continuous vocalization and echoreception. Sounds from nearby conspecifics may have a similar spectrum and high intensity. Bats emitting frequency-modulated (FM) echolocation calls avoid conspecific jamming sounds by altering their call frequency jamming avoidance response (JAR). Bats emitting constant frequency (CF)-FM can use other strategies to avoid jamming due to the different functions of the two acoustic components. In this study, seven Rhinolophus sinicus bats were used to conduct sound detection in both single individuals and pairs. We studied how these bats adjust the terminal FM (tFM) component of their calls when flying with conspecifics, and we tested whether acoustic adjustments are made to avoid jamming. Echolocation calls had shorter durations, reduced pulse intervals and higher tFM peak frequency and terminal frequency in the presence of conspecifics. The frequency differences of the tFM component between two bats did not increase in paired flights compared to their baseline difference, and the magnitude of spectral adjustments was independent of the baseline separations between bats. These results suggest that these bats do not use a JAR strategy to mitigate interference in the tFM component of calls. The call adjustments of CF-FM bats are more likely to be attention behaviours rather than being used for avoiding acoustic interference. Bats differentiate their own echoes and pulses from those of conspecifics through their respective acoustic signatures.