Division of Evolution, Ecology and Genetics, Research School of Biology, Australian National University, Canberra 0200, Australia.
Proc Biol Sci. 2009 Dec 7;276(1676):4173-9. doi: 10.1098/rspb.2009.1110. Epub 2009 Sep 2.
Animals often form groups to increase collective vigilance and allow early detection of predators, but this benefit of sociality relies on rapid transfer of information. Among birds, alarm calls are not present in all species, while other proposed mechanisms of information transfer are inefficient. We tested whether wing sounds can encode reliable information on danger. Individuals taking off in alarm fly more quickly or ascend more steeply, so may produce different sounds in alarmed than in routine flight, which then act as reliable cues of alarm, or honest 'index' signals in which a signal's meaning is associated with its method of production. We show that crested pigeons, Ocyphaps lophotes, which have modified flight feathers, produce distinct wing 'whistles' in alarmed flight, and that individuals take off in alarm only after playback of alarmed whistles. Furthermore, amplitude-manipulated playbacks showed that response depends on whistle structure, such as tempo, not simply amplitude. We believe this is the first demonstration that flight noise can send information about alarm, and suggest that take-off noise could provide a cue of alarm in many flocking species, with feather modification evolving specifically to signal alarm in some. Similar reliable cues or index signals could occur in other animals.
动物通常会形成群体以提高集体警戒，从而能够更早地发现捕食者，但这种社交的好处依赖于信息的快速传递。在鸟类中，并非所有物种都有警报声，而其他被提议的信息传递机制效率低下。我们测试了翅膀的声音是否可以编码有关危险的可靠信息。处于警戒状态下起飞的个体飞得更快或上升得更陡峭，因此可能会在警报声和常规飞行中产生不同的声音，这些声音可以作为警报的可靠提示，或者是诚实的“指标”信号，其中信号的含义与其产生方式相关联。我们发现，冠鸽（Ocyphaps lophotes），一种具有改良飞行羽毛的鸟类，在警戒飞行中会发出独特的翅膀“哨声”，并且只有在播放警报哨声后，个体才会发出警报起飞。此外，对振幅进行了调整的播放实验表明，响应取决于哨声的结构，如节奏，而不仅仅是振幅。我们认为这是首次证明飞行噪音可以传递有关警报的信息的证明，并表明起飞噪音可能会为许多成群结队的物种提供警报的线索，而羽毛的改良则专门用于在某些物种中发出警报。类似的可靠线索或指标信号可能会在其他动物中出现。
