Museum of Vertebrate Zoology, University of California, Berkeley, California 94720, USA.
Am Nat. 2010 Jan;175(1):27-37. doi: 10.1086/648560.
Courtship displays frequently include complex signals that females use to pick a mate. Male Costa's hummingbirds (Calypte costae) generate two acoustic signals during courtship: a vocal song produced close to a female and a dive-sound produced during a courtship dive. The song and dive-sound sound similar, and both were assumed to be produced vocally by the syrinx. Here, we show that they are not; whereas the song is produced by the syrinx, the dive-sound is produced by high-frequency fluttering of the outermost tail feathers. The Anna's hummingbird (Calypte anna), sister to the Costa's, also sings a vocal song and produces a dive-sound with the wings and outermost tail feathers that sounds similar to a portion of the song. The interspecific match in signal form between the two species is not as strong as the intraspecific match. Phylogenetic reconstruction indicates that the dive-sounds may have evolved first, suggesting that the song may have evolved to mimic the dive-sound. We propose the "sexual sensory bias" hypothesis as an explanation for the match in form between the song and the dive-sound within each species, in which we suggest that new sexual signals can arise in response to preexisting female preferences for older sexual signals.
求偶展示通常包括复杂的信号，雌性利用这些信号来选择配偶。雄性 Costa 的蜂鸟（Calypte costae）在求偶期间会发出两种声学信号：一种是靠近雌性发出的声乐歌曲，另一种是在求偶俯冲时发出的俯冲声。歌曲和俯冲声听起来很相似，两者都被认为是由鸣管发出的。在这里，我们表明并非如此；虽然歌曲是由鸣管发出的，但俯冲声是由最外面的尾羽高频颤动产生的。Costa 的蜂鸟的姐妹 Anna 的蜂鸟（Calypte anna）也会发出声乐歌曲，并通过翅膀和最外面的尾羽发出类似于歌曲一部分的俯冲声。两种物种之间信号形式的种间匹配不如种内匹配强。系统发育重建表明，俯冲声可能首先进化而来，这表明歌曲可能是为了模仿俯冲声而进化的。我们提出“性感觉偏见”假说作为对每个物种中歌曲和俯冲声形式匹配的解释，我们认为新的性信号可以响应女性对旧性信号的预先存在的偏好而产生。
