Radford Andrew N, Ridley Amanda R
School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, UK.
Biol Lett. 2007 Jun 22;3(3):249-52. doi: 10.1098/rsbl.2007.0110.
Many studies of social species have reported variation in the anti-predator vigilance behaviour of foraging individuals depending on the presence and relative position of other group members. However, little attention has focused on how foragers assess these variables. It is commonly assumed that they do so visually, but many social species produce frequent calls while foraging, and these 'close' calls might provide valuable spatial information. Here, we show that foraging pied babblers (Turdoides bicolor) are less vigilant when in larger groups, in the centre of a group and in closer proximity to another group member. We then show that foragers are less vigilant during playbacks of close calling by more individuals and individuals on either side of them when compared with calls of fewer individuals and calls on one side of them. These results suggest that foragers can use vocal cues to gain information on group size and their spatial position within a group. Future studies of anti-predator vigilance should consider the relative importance of both visual and vocal monitoring of group members.
许多关于群居物种的研究报告称，觅食个体的反捕食警惕行为会因其他群体成员的存在和相对位置而有所不同。然而，很少有研究关注觅食者如何评估这些变量。人们通常认为它们是通过视觉来评估的，但许多群居物种在觅食时会频繁发出叫声，而这些“近距离”叫声可能会提供有价值的空间信息。在这里，我们表明，觅食的双色蚁鵙在群体规模较大、处于群体中心以及与另一个群体成员距离更近时，警惕性会降低。然后我们表明，与较少个体的叫声以及一侧的叫声相比，当更多个体以及两侧的个体发出近距离叫声时，觅食者在回放这些叫声时的警惕性会降低。这些结果表明，觅食者可以利用声音线索来获取关于群体规模及其在群体中空间位置的信息。未来关于反捕食警惕性的研究应考虑对群体成员进行视觉和声音监测的相对重要性。
