Age Differences in the responses of vervet monkeys to terrestrial alarm calls

Here, we explore the development of alarm call responses in wild vervet monkeys (Chlorocebus pygerythrus) living at the Samara Game Reserve, South Africa. Vervet monkeys at this site live in relatively large social groups, and adult responses to alarms have previously shown less uniformity than in other sites where group sizes are smaller. We presented monkeys played back recordings of terrestrial alarm calls produced by individuals of different age/sex classes. We then video-recorded and scored the responses of receivers along an ordinal maturity scale. We used a mixed-effects ordinal logistic regression model within a Bayesian framework to explore how response intensity is affected by the age/sex of the caller, and the age of receivers. Our analysis showed that younger monkeys (<2yrs) exhibit strong evasive responses to call stimuli, regardless of the age/sex class of the caller. The intensity of these responses decreases with age, with responses to non-alarm calls decreasing earlier in
development compared to alarm calls. Adult responses to alarms in this population are equally as likely to be characterized by a general increase in vigilance as they are to consist of an evasive response. We suggest that responses in younger individuals at Samara are mediated by a generalized startle responses to loud, plosive noises. Development of more specific responses throughout ontogeny is likely to be dependent
on learning from adult models, whose milder responses reflect specific to local socioecological conditions at Samara.

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在本研究中，我们探讨了生活在南非萨马拉野生动物保护区（Samara Game Reserve）的野生绿猴（Chlorocebus pygerythrus）对警报声的响应发展。该地区的绿猴生活在相对较大的社会群体中，与群体规模较小的其他地区相比，成年绿猴对警报声的响应在一致性方面表现出较少的统一性。我们向猴子播放了由不同年龄/性别类别的个体产生的陆地警报声录音。随后，我们通过视频记录并评分接收者的响应，按照成熟度等级进行排序。在贝叶斯框架内，我们运用混合效应有序逻辑回归模型来探究响应强度受呼叫者年龄/性别和接收者年龄的影响。我们的分析表明，年轻猴子（<2岁）对呼叫刺激表现出强烈的逃避反应，无论呼叫者的年龄/性别类别如何。这些反应的强度随着年龄的增长而降低，与警报声相比，非警报声的响应在发育早期就减少了。该种群成年对警报声的响应，既可能是由于警觉性的普遍提高，也可能是由于逃避反应。我们认为，萨马拉地区年轻个体的反应是由对响亮、爆裂声的普遍惊吓反应所介导的。在整个个体发育过程中，更具体的反应的发展可能取决于从成年模型的学习，成年模型的较轻微反应反映了萨马拉地区特定的社会生态条件。