| Summary: | 碩士 === 國立臺灣大學 === 森林環境暨資源學研究所 === 105 === The time, space and frequency range of sounds are limited resources for animals communicating by sounds. With increasing sounds in environment, the sound signals interfere with each other, resulting in acoustic competition among animals. To reduce acoustic competition, sympatric animals often differentiate their acoustic frequency range or time to produce sound. In lower elevation forests of Taiwan, it is often found that avian sounds are severely suppressed by sounds of cicadas. In order to determine whether cicadas interfere with avian vocal behavior and examine important factors in the sound competition between cicadas and birds, I used automated acoustic recorders to monitor the sounds of the local birds and cicadas in Erziping area of Yangmingshan National Park. Also, I conducted indoor playback experiments on wild Light-vented Bulbuls (Pycnonotus sinensis) to examine the effects of cicada species, cicada sound frequency and intensity on their vocal behavior. Field recordings in Erziping showed that cicada sounds interfered with avian vocal behavior. Bird species with higher overlap of sound frequency with the cicada Tanna sozanensis were more likely disturbed by the cicadas and avoided producing sound with the cicadas simultaneously. Indoor playback experiments showed that Light-vented Bulbuls significantly reduced calling when sounds of Tanna sozanensis were played. This avoidance tendency was more significant with higher intensity of cicada sounds or higher overlap with sound frequency of Light-vented Bulbuls. This study confirms that cicadas seriously disturb avian vocal behavior and frequency overlap and sound intensity are key factors. Broad frequency and high intensity of cicada sounds would force birds to avoid calling simultaneously with cicadas in order to reducing acoustic competition. However, this impact of cicada sounds on avian vocal behavior might be limited if their sound frequencies was less overlapped. Acoustic competition between cicadas and birds should be taken into consideration for future studies of avian vocal behavior in lower elevations of Taiwan.
|
|---|
