Call-timing plasticity of a treefrog in response to noise

Abstract

Chorusing animals constantly face the challenge of overcoming background noises. To minimize the masking of their own calls by conspecific or heterospecific calls, plasticity in call timing serves as an alternative tactic for chorusing animals. We examined how male rhacophorid treefrogs, Zhangixalus prasinatus, adjust their call timing in response to various noisy environments. When exposed to periodic white noise disturbances with brief silent intervals, the frogs accurately avoided overlapping with the noise and delivered their calls in the silent gaps. Moreover, they delivered long calls earlier than short calls during the silent periods to accommodate the longer duration within a brief silent gap. When exposed to noises of varying frequencies, the frogs specifically avoided medium-frequency noise, which closely matched their own call frequency. This phenomenon was also observed in experiments testing the aggregating behaviour of male frogs; they ceased to aggregate towards conspecific calls when interfered with by medium-frequency noise, whereas high-frequency and low-frequency noise interferences did not elicit the same behaviour. Compared to high-quality males, frogs with low SM_i (scaled mass index) exhibited greater plasticity in call timing, indicating a condition-dependent tactic for energy allocation. Such behavioural plasticity in call timing was reflected in natural soundscape recordings. Our recordings revealed that, as a result of these adaptive strategies, males tended to avoid overlapping their calls with background noises in their natural habitats. Our research provides evidence that call plasticity is an effective strategy for chorusing animals to respond to noise at both individual and population levels. Furthermore, our study suggests that plasticity in call timing is a complex decision-making behaviour involving the consideration of noise properties and an individual's body condition.