Characterization of acoustic traits and seasonal calling pattern of Dryophytes japonicus rain calls: a potential bioindicator of climate change

초록

Amphibians are sensitive to environmental change owing to their permeable skin and ectothermic nature. Frog calls can serve as bioindicators because call features and calling activity vary according to environmental factors. Treefrogs emit both advertisement and rain calls. Unlike advertisement calls, which are emitted at night and to attract mates, few studies have examined rain calls emitted during daytime. This study investigated the acoustic properties and seasonal calling patterns of Dryophytes japonicus rain calls, recorded in lowland woodlands near rice paddies. Rain calls occurred during daytime in both the breeding and nonbreeding seasons, whereas advertisement calls occurred exclusively after sunset during the breeding season. The rain calls had lower dominant frequencies, fewer notes, shorter note durations, and more rapid note repetition rates than advertisement calls. The calling activity for rain calls was significantly influenced by the time of day, air temperature, and humidity, regardless of the season. Unlike advertisement calls, rain calls are emitted during the daytime in the breeding and nonbreeding seasons, suggesting that they have specific functions and should be investigated in the future. Given the vocalizations of D. japonicus during the breeding and nonbreeding seasons, along with its pronounced sensitivity to environmental factors, the calling activity of D. japonicus may be used as a bioindicator of climate change.

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