Effects Of Ambient Noise On The Birdsong

The studies of the effects of ambient noise on the vocal amplitudes, structure and frequency of birdsong were carried out in urban and suburb zones of Hangzhou City and Lin'an in Zhejiang Province and Fuyang in Anhui Province between September 2002 and April 2004. Based on the noise level (55dB), high noise localities (HN) and low noise localities (LN) were selected and the study was done on the relationship between structure and frequency of birdsong and the ambient noise in three cities, from Sep 2002 to Apr 2004.The result of study on the vocal amplitudes of birdsong in Hangzhou City showed that the sound pressure level of songs of Chinese Bulbul, Pycnonotus sinensis, and Eurasian Tree Sparrow, Passer montanus, was significantly related to the ambient noise level based on linear regression analysis (for Chinese Bulbul: Y=0.676X+22.981, R2=0.783, t=13.163, F=173.257, PO.001 and for Eurasian Tree Sparrow: Y-0.751X +17.036, R2=0.738, t=3.674, F=64.893, P=0.001). It suggested that both Chinese Bulbul and Eurasian Tree Sparrow would enhanced their sound pressure levels as the increasing of noise levels in their habitats.The comparative study on the characteristics of song structure and frequency, such as sonagrams, frequency spectrum of the full sentences and the data of principal frequency (PF) of syllable, of Chinese Bulbul in high noise localities (HN) and low noise localities (LN) showed that the number and interval of syllables had differences between HN and LN in three study areas on the song structure of Chinese Bulbuls. More numbers of syllables, more complex song structure and longer interval of syllables were recorded in HN. The songs of Chinese Bulbuls had one obvious main energy peak and one or two harmonics of high frequency with higher energy in HN, but it had only one harmonic of high frequency with lowerenergy asides main energy peak in LN. The minimum PF and maximum PF of all syllables and PF of first syllable (S) and second syllable (S) of each sentence had significant differences between HN and LN in Lin'an and Fuyang. In Fuyang, the third syllable (S) had significant difference because of geographic diversity. In Hangzhou, however, only the first syllable (S) and the second syllable (S ) of every song had significant differences between HN and LN.With the fast development of urbanization, the vocal communication of birds was mostly disturbed by human activities, especially the anthropogenic noise. It was very important for birds to regulate their vocalization to communicate with each other effectively so that the species could survive and brood in noisy environment. The Chinese Bulbuls was able to avoid the effect of the ambient noise by changing the vocal amplitude and frequency and the structure of song of itself, so that it could pass the vocal information accurately hi noisy environment. Just because of its song plasticity that other species lack, Chinese Bulbuls had higher adaptabilities. It's probably the one reason why Chinese Bulbuls could survive and breed in high noise environment in cities and become the wide distributed species. -...