Background Birds can maximize their reproductive success through careful selection of nest-sites. The ‘total-foliage’ hypothesis predicts that nests concealed in vegetation should have higher survival. We propose an additional hypothesis, the ‘predator proximity’ hypothesis, which states that nests placed farther from predators would have higher survival. We examined these hypotheses in the world’s southernmost forests of Navarino Island, in the Cape Horn Biosphere reserve, Chile (55°S). This island has been free of mammalian ground predators until recently, and forest passerines have been subject to depredation only by diurnal and nocturnal raptors. Methods During three breeding seasons (2014–2017), we monitored 104 nests for the five most abundant open-cup forest-dwelling passerines (Elaenia albiceps, Zonotrichia capensis, Phrygilus patagonicus, Turdus falcklandii, and Anairetes parulus). We identified nest predators using camera traps and assessed whether habitat characteristics affected nest-site selection and survival. Results Nest predation was the main cause of nest failure (71% of failed nests). Milvago chimango was the most common predator, depredating 13 (87%) of the 15 nests where we could identify a predator. By contrast, the recently introduced mammal Neovison vison, the only ground predator, depredated one nest (7%). Species selected nest-sites with more understory cover and taller understory, which according to the total-foliage hypothesis would provide more concealment against both avian and mammal predators. However, these variables negatively influenced nest survival. The apparent disconnect between selecting nest-sites to avoid predation and the actual risk of predation could be due to recent changes in the predator assemblage driven by an increased abundance of native M. chimango associated with urban development, and/or the introduction of exotic mammalian ground predators to this island. These predator assemblage changes could have resulted in an ecological trap. Further research will be needed to assess hypotheses that could explain this mismatch between nest-site selection and nest survival.

中文翻译：

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雀形目在世界最南端森林的巢址选择和繁殖成功

背景 通过仔细选择巢址，鸟类可以最大限度地提高繁殖成功率。“全叶”假说预测隐藏在植被中的巢穴应该有更高的存活率。我们提出了一个额外的假设，即“捕食者接近”假设，该假设指出离捕食者越远的巢穴存活率越高。我们在智利合恩角生物圈保护区（南纬 55°）世界最南端的纳瓦里诺岛森林中检验了这些假设。直到最近，这个岛上还没有哺乳动物的地面捕食者，森林雀形目只受到昼夜猛禽的掠夺。方法 在三个繁殖季节（2014-2017 年），我们监测了 104 个巢穴中 5 种最丰富的开放式林栖雀形目（Elenaia albiceps、Zonotrichia capensis、Phrygilus patagonicus、Turdus falcklandii 和 Anairetes parulus)。我们使用相机陷阱识别巢穴捕食者，并评估栖息地特征是否影响巢穴选择和生存。结果 巢穴捕食是巢穴失败的主要原因（71% 的失败巢穴）。Milvago chimango 是最常见的捕食者，掠夺了我们可以识别捕食者的 15 个巢穴中的 13 个（87%）。相比之下，最近引入的哺乳动物 Neovison vison，唯一的地面捕食者，掠夺了一个巢穴 (7%)。物种选择了具有更多林下覆盖和更高林下的巢穴，根据全叶假设，这将为鸟类和哺乳动物捕食者提供更多的隐蔽性。然而，这些变量对巢穴的生存产生了负面影响。选择巢址以避免捕食与实际捕食风险之间的明显脱节可能是由于与城市发展相关的本地 M. chimango 数量增加和/或外来哺乳动物的引入导致捕食者组合的最近变化将食肉动物带到这个岛上。这些捕食者组合的变化可能导致生态陷阱。需要进一步的研究来评估可以解释巢址选择和巢生存之间的这种不匹配的假设。