城市噪声使树麻雀鸣唱的最低频率升高

Urban Noise Increases the Minimum Frequency of Tree Sparrow(Passer montanus)Songs

随着城市化进程的不断加快,城市噪声水平显著升高。噪声会掩盖鸟类的声音信号,这无疑会影响鸟类的交流。在嘈杂的城市环境中,鸟类通常以高频率鸣唱来避免声信号被掩蔽。然而,较低的发声频率才是雄性品质的重要表征,提高发声频率可能会影响声信号对雌性的吸引力。因此,鸟类会在提高发声频率和保持较低频率之间进行权衡。为确定城市噪声对树麻雀(Passer montanus)鸣唱行为的影响,在沈阳市选取6个研究地点,比较了沈阳市区和近郊不同噪声水平下树麻雀繁殖期的鸣唱特征。在2019年4月至7月,使用定向麦克风录制了320只繁殖期树麻雀的鸣唱,并使用声级计测定噪声水平。研究结果显示,城市研究地点的噪声水平显著高于郊区研究地点。与安静郊区相比,城市嘈杂环境中的树麻雀鸣唱的最高频率、最低频率和主峰峰频显著较高,频宽更大,而时长没有差别。树麻雀鸣唱的最高频率、频宽、主峰峰频和时长均与噪声水平无显著相关,而最低频率与研究地点的噪声水平呈显著正相关。上述结果说明,在噪声环境中,树麻雀选择提高最低频率以利于声信号的传输。

With the continuous acceleration of urbanization,noise levels in urban areas have significantly increased,which could mask the communication signals and thus pose a challenge to vocal communication of birds.Because the frequency of urban noise is generally low,birds could sing at high frequencies to avoid being masked in noisy urban environments.Lower frequency of vocalizations is an important indicator of male quality,however,the higher frequency of vocalizations would reduce the attractiveness of the vocalizations to females.Consequently,there is a trade-off for birds between raising and keeping vocalization frequency.With the aim to examine the effects of urban noise on vocalization of Tree Sparrows(Passer montanus),we compared the breeding songs of tree sparrows at six study sites in Shenyang with different noise levels from April to July 2019.We recorded the songs of Tree Sparrows at breeding stage using directional microphones and measured noise levels using a calibrated sound pressure level meter.Differences in song parameters and noise levels between urban and suburban sampling sites were analyzed by nested ANOVA.The Unary linear regression analysis was carried out on the mean of song parameters and the mean of noise for six study point tree sparrows,with noise level as an independent variable.Our results showed that the urban sites had higher noise levels than the suburban sites(P<0.01,Table 2).Tree Sparrows in the urban sites had significantly higher maximum frequency(P<0.01),higher minimum frequency(P<0.05),higher peak frequency(P<0.01),and wider bandwidth(P<0.01)(Table 2).There was no significant difference of vocalization duration between tree sparrows in urban and suburban sites(P>0.05,Table 2).The maximum frequency(P>0.05),bandwidth(P>0.05),peak frequency(P>0.05),and duration(P>0.05)were not significantly correlated with the noise(P>0.05)(Fig.3).The minimum frequency was positively correlated with the noise level(P<0.01,Fig.3).Our results indicated that,Tree Sparrows choose to increase the minimum frequency for better signal transmission in noisy environments.