Rainfall and Temperature Explain Colony Variation in Echolocation Calls of the Intermediate Horseshoe Bats...

Geographic variation in acoustic signals of animals is shaped by both environmental conditions and morphology related to vocal production. However, the drivers of call variation among colonies at a landscape scale remain largely uncertain. This study aimed to assess the determinants of colony-level variation in echolocation calls of intermediate horseshoe bats (Rhinolophus affinis) from the southern and northern regions of the Funiu Mountains in central China. We recorded echolocation calls emitted by 129 resting adult bats from eight cave-dwelling colonies and measured the spectro-temporal parameters of their calls. We obtained forearm lengths of bats, climate variables, and the normalized difference vegetation index to evaluate their effects on echolocation call variation among colonies. Our analyses showed that the duration and peak frequency of echolocation calls varied among colonies and between sexes. Males produced echolocation calls of longer durations and lower peak frequencies relative to females. Monthly mean precipitation was positively associated with the peak frequency of echolocation calls in males. The monthly mean temperature was negatively associated with the peak frequency of echolocation calls in females. In both males and females, call duration and peak frequency were not significantly affected by forearm length, altitude, or normalized difference vegetation index. The structural equation model further indicated that monthly mean precipitation and temperature had direct effects on call frequency of males and females, respectively. These results provide correlative evidence in favor of the sensory drive hypothesis, indicating that rainfall and ambient temperature shape echolocation call divergence in horseshoe bats at the landscape scale.