BackgroundThere is limited knowledge about the breeding strategies of birds inhabiting in South American temperate forests. This is particularly true for open-cup forest passerines breeding at high latitudes (> 42°). To better understand the ecology of these species, in this study we described and compared the breeding strategies (i.e., nest dimensions, nest height from the ground, egg laying rhythm, clutch size, length of the developmental periods, breeding phenology, and diversity of nesting substrate) of five passerine birds that inhabit sub-Antarctic ecosystems.MethodsDuring three breeding seasons (2014–2017), we monitored 103 nests of the five most abundant open-cup forest-dwelling passerines (Phrygilus patagonicus, Anairetes parulus, Turdus falcklandii, Elaenia albiceps, and Zonotrichia capensis) on Navarino Island (55°S), Cape Horn Biosphere Reserve, southern Chile. Additionally, we compared the breeding strategies of T. falcklandii to another population breeding at lower latitude (39°S).ResultsMost of the species started laying eggs the last week of September; only E. albiceps started 2 months later. During the breeding season of 2016–2017 both E. albiceps and Z. capensis started laying eggs earlier than the previous year. Anairetes parulus and Z. capensis were the most specialized in terms of nesting substrate. Turdus falcklandii had larger clutch sizes and nested closer to the ground on Navarino Island compared to the northern population, which might put this and other ground nesting species of this island at a higher risk of predation by the recently introduced American mink (Neovison vison).ConclusionsOur five study species breed exclusively in open-cups (not in cavities) in sub-Antarctic forests, and some of them built their nests closer to the ground compared to populations breeding at lower latitudes. This may be associated with the lack of terrestrial predators on Navarino Island. Our study opens further questions about the mechanisms driving differences in breeding strategies among populations.

中文翻译：

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智利纳瓦里诺岛亚南极森林中开杯筑巢鸟类的繁殖策略

背景对栖息在南美温带森林的鸟类的繁殖策略知之甚少。对于在高纬度（> 42°）繁殖的开杯森林雀类尤其如此。为了更好地了解这些物种的生态，在本研究中，我们描述并比较了繁殖策略（即巢尺寸、巢距地面的高度、产卵节奏、离合器大小、发育期长度、繁殖物候和多样性栖息在亚南极生态系统中的五只雀鸟的筑巢基质）。方法在三个繁殖季节（2014-2017 年），我们监测了五种最丰富的开杯森林栖息雀鸟（Phrygilus patagonicus、Anairetes parulus、Turdus falcklandii、纳瓦里诺岛 (55°S) 上的 Elaenia albiceps 和 Zonotrichia capensis)，合恩角生物圈保护区，智利南部。此外，我们还比较了福克兰伊蚊与另一个低纬度（39°S）种群的繁殖策略。结果大多数物种在 9 月的最后一周开始产卵；只有 E. albiceps 在 2 个月后开始。在 2016-2017 年的繁殖季节，E. albiceps 和 Z. capensis 都比前一年更早开始产卵。Anairetes parulus 和 Z. capensis 在筑巢基质方面最为专业。与北部种群相比，Turdus falcklandii 具有更大的离合器尺寸，并且在纳瓦里诺岛上筑巢更靠近地面，这可能会使该岛的这个和其他地面筑巢物种面临更高的被最近引入的美国水貂（Neovison vison）捕食的风险。结论我们的五个研究物种仅在亚南极森林中的开放杯中（而不是在洞穴中）繁殖，与在低纬度繁殖的种群相比，其中一些物种的巢穴更靠近地面。这可能与纳瓦里诺岛上缺乏陆地捕食者有关。我们的研究进一步探讨了导致种群间育种策略差异的机制。