Nelson Brian S, Beckers Gabriël J L, Suthers Roderick A
Department of Biology, Indiana University, Bloomington, IN 47405, USA.
J Exp Biol. 2005 Jan;208(Pt 2):297-308. doi: 10.1242/jeb.01378.
Bird vocalizations resonate as they propagate through a relatively long trachea and radiate out from the oral cavity. Several studies have described the dynamics with which birds actively vary beak gape while singing and it has been hypothesized that birds vary beak gape as a mechanism for varying vocal tract resonances. Nevertheless, few studies have attempted to quantify the effects of beak gape on vocal tract resonances. We replaced eastern towhee, Pipilo erythrophthalmus L., syringes with a small speaker and obtained recordings of frequency sweeps while rotating each subject in a horizontal plane aligned with either the maxilla or mandible. We describe vocal tract resonances as well as how sound radiates as a function of beak gape. Results are inconsistent with the hypothesis that songbirds vary beak gape as a mechanism for 'tracking' fundamental frequencies in vocalizations. Instead, decreases in beak gape seem to attenuate resonances that occur between approximately 4 and 7.5 kHz. We propose that songbirds vary beak gape as a mechanism for excluding and/or concentrating energy within at least two distinct sound frequency channels.
鸟类的叫声在通过相对较长的气管传播并从口腔辐射出去时会产生共鸣。几项研究描述了鸟类在歌唱时主动改变喙张开度的动态过程，并且有人推测鸟类改变喙张开度是一种改变声道共振的机制。然而，很少有研究试图量化喙张开度对声道共振的影响。我们用一个小扬声器替换了东美洲雀鹀（Pipilo erythrophthalmus L.）的鸣管，并在将每个实验对象在与上颌或下颌对齐的水平面上旋转时获取了频率扫描记录。我们描述了声道共振以及声音如何作为喙张开度的函数进行辐射。结果与鸣禽改变喙张开度作为在发声中“追踪”基频的机制这一假设不一致。相反，喙张开度的减小似乎会减弱大约4至7.5千赫兹之间出现的共振。我们提出，鸣禽改变喙张开度是一种在至少两个不同的声音频率通道内排除和/或集中能量的机制。
