扬子鳄幼鳄出壳前后的鸣声特征比较

Spectrotemporal Characteristics of Vocalizations of Pre-and Post-hatching Yangtze Alligators (Alligator sinensis)

成年扬子鳄(Alligator sinensis)的声信号已经有过深入的研究,然而其声音的个体发育,特别是幼鳄出壳前后鸣声的时空特征至今还不为人所知。为了解扬子鳄声音的发育过程,记录和分析了21只扬子鳄幼鳄的260个叫声,结果表明,幼鳄出壳前后的鸣声具有相似的特征,即开始向上的频率调节和较长的向下的频率调节。出壳前和出壳后的两组叫声均包括持续叠加的多组谐波,并且绝大多数的鸣声都是在第3谐波显示了最强的能量。分析了出壳前后鸣声的9个参数,即总时长、向上调频的时长、向下调频的时长、基频的起始频率、最高频率、结束频率、向上调频的倾斜度、向下调频的倾斜度、主频。除了向上调频的时长,出壳前后鸣声的其他时长参数均没有表现出显著差异。与之相反的是,出壳前后鸣声的频谱参数,特别是基频的最高频率和主频均表现出显著差异(P<0.05)。出壳前鸣声基频的最高频率为(573±103)Hz,出壳后的声音最高频率(460±52)Hz,出壳前比出壳后高113 Hz;出壳前的声音主频(1 359±229)Hz,出壳后的声音主频(1 123±216)Hz,前者比后者高236 Hz。幼鳄发出主频较高的鸣叫有利于吸引附近母鳄的注意同时避免天敌的捕食。

The vocal signals of adult Yangtze Alligators （Alligator sinensis） have been well characterized. The ontogeny of their vocalizations, however, is poorly understood and calls of pre-hatching and newly hatched alligators have never been described before. In present study, using a digital audio recorder and sound analysis software, we recorded and analyzed 260 calls of 21 pre- and post-hatching alligators. We found that the calls of both groups have similar spectrotemporal characteristics featuring an initial upward frequency modulation （FM） followed by a longer downward FM （Fig. 1）. Calls of pre- and post-hatching alligators similarly contain a rich stack of harmonics with the third harmonic showing the strongest energy （Fig. 2 and Fig. 3）. Nine call parameters （total duration, duration of upward FM, duration of downward FM, initial fundamental frequency [F0], maximum F0, terminal F0, slopes of upward frequency modulation [FM] and of downward FM, and dominant frequency [DF]） were analyzed and compared between pre- and post-hatching alligators. Statistical tests （Independent-Samples T Tests） revealed that all temporal parameters, with the exception of the duration of upward FM, were not significantly different between the two groups. In contrast, all spectral parameters, most notably the maximum F0 and the DF, differed significantly between two groups （P 〈 0.05）. The average maximum F0 for pre-hatching alligators （573 ±103 Hz） was 113 Hz higher than that for post-hatching alligators （460 ±52 Hz）; the average DF for pre-hatching alligators （1 359 ± 229 Hz） was 236 Hz higher than that for post-hatching alligators （1 123 ± 216 Hz） （Fig. 1, Table 1）. These results suggested that the higher dominant frequency of pre-hatching Yangtze Alligator calls is advantageous for calling the attention of nearby maternal alligator while avoiding predation by distal predators.