Department of Natural Resources, Cornell University, Ithaca, New York, United States of America.
PLoS One. 2013 Dec 6;8(12):e82384. doi: 10.1371/journal.pone.0082384. eCollection 2013.
The threat sensitivity hypothesis predicts that organisms will evaluate the relative danger of and respond differentially to varying degrees of predation threat. Doing so allows potential prey to balance the costs and benefits of anti-predator behaviors. Threat sensitivity has undergone limited testing in the auditory modality, and the relative threat level of auditory cues from different sources is difficult to infer across populations when variables such as background risk and experience are not properly controlled. We experimentally exposed a single population of two sympatric gull species to auditory stimuli representing a range of potential threats in order to compare the relative threat of heterospecific alarm calls, conspecific alarms calls, predator vocalizations, and novel auditory cues. Gulls were able to discriminate among a diverse set of threat indicators and respond in a graded manner commensurate with the level of threat. Vocalizations of two potential predators, the human voice and bald eagle call, differed in their threat level compared to each other and to alarm calls. Conspecific alarm calls were more threatening than heterospecfic alarm calls to the larger great black-backed gull, but the smaller herring gull weighed both equally. A novel cue elicited a response intermediate between known threats and a known non-threat in herring gulls, but not great black-backed gulls. Our results show that the relative threat level of auditory cues from different sources is highly species-dependent, and that caution should be exercised when comparing graded and threshold threat sensitive responses.
威胁敏感假说预测，生物将评估不同程度捕食威胁的相对危险，并做出不同的反应。这样做可以使潜在的猎物平衡反捕食行为的成本和收益。威胁敏感性在听觉模态中受到的测试有限，并且当背景风险和经验等变量没有得到适当控制时，很难从不同种群中推断出来自不同来源的听觉线索的相对威胁程度。我们通过实验使单一的两个滨鸟物种群体暴露于一系列潜在威胁的听觉刺激下，以比较异种种群警报声、同种警报声、捕食者叫声和新的听觉线索的相对威胁程度。海鸥能够识别出各种不同的威胁指标，并根据威胁程度做出相应的分级反应。两种潜在捕食者（人类声音和白头鹰叫声）的发声与彼此相比，以及与警报声相比，其威胁程度有所不同。对于较大的大黑背鸥来说，同种警报声比异种种群警报声更具威胁性，但较小的银鸥则将两者同等对待。在银鸥中，一个新的线索引起的反应在已知威胁和已知非威胁之间处于中间位置，但在大黑背鸥中则不然。我们的结果表明，来自不同来源的听觉线索的相对威胁程度高度依赖于物种，因此在比较分级和阈值敏感的威胁反应时应谨慎行事。
