Podos Jeffrey, Southall Joel A, Rossi-Santos Marcos R
Department of Biology, University of Massachusetts, Amherst, MA 01003, USA.
J Exp Biol. 2004 Feb;207(Pt 4):607-19. doi: 10.1242/jeb.00770.
Recent studies of vocal mechanics in songbirds have identified a functional role for the beak in sound production. The vocal tract (trachea and beak) filters harmonic overtones from sounds produced by the syrinx, and birds can fine-tune vocal tract resonance properties through changes in beak gape. In this study, we examine patterns of beak gape during song production in seven species of Darwin's finches of the Galápagos Islands. Our principal goals were to characterize the relationship between beak gape and vocal frequency during song production and to explore the possible influence therein of diversity in beak morphology and body size. Birds were audio and video recorded (at 30 frames s(-1)) as they sang in the field, and 164 song sequences were analyzed. We found that song frequency regressed significantly and positively on beak gape for 38 of 56 individuals and for all seven species examined. This finding provides broad support for a resonance model of vocal tract function in Darwin's finches. Comparison among species revealed significant variation in regression y-intercept values. Body size correlated negatively with y-intercept values, although not at a statistically significant level. We failed to detect variation in regression slopes among finch species, although the regression slopes of Darwin's finch and two North American sparrow species were found to differ. Analysis within one species (Geospiza fortis) revealed significant inter-individual variation in regression parameters; these parameters did not correlate with song frequency features or plumage scores. Our results suggest that patterns of beak use during song production were conserved during the Darwin's finch adaptive radiation, despite the evolution of substantial variation in beak morphology and body size.
近期对鸣禽发声机制的研究已经确定了喙在声音产生中的功能作用。声道（气管和喙）会过滤掉鸣管产生声音中的谐波泛音，并且鸟类可以通过改变喙的张开度来微调声道的共振特性。在本研究中，我们研究了加拉帕戈斯群岛七种达尔文雀在鸣叫时喙张开的模式。我们的主要目标是描述鸣叫时喙张开度与发声频率之间的关系，并探讨喙形态和体型差异可能对其产生的影响。在野外，当鸟类鸣叫时，对它们进行音频和视频记录（每秒30帧），并分析了164个鸣叫序列。我们发现，在所研究的56只个体中的38只以及所有七个物种中，鸣叫频率与喙张开度呈显著正相关。这一发现为达尔文雀声道功能的共振模型提供了广泛支持。物种间的比较显示回归y轴截距值存在显著差异。体型与y轴截距值呈负相关，尽管未达到统计学显著水平。尽管发现达尔文雀和两种北美麻雀物种的回归斜率不同，但我们未能检测到雀类物种间回归斜率的差异。对一个物种（勇地雀）的分析显示回归参数存在显著的个体间差异；这些参数与鸣叫频率特征或羽毛评分无关。我们的结果表明，尽管喙形态和体型发生了显著变化，但在达尔文雀的适应性辐射过程中，鸣叫时喙的使用模式得以保留。
