Abstract Understanding the mechanisms underpinning nest-site selection offers novel insights about selective forces shaping the breeding ecology of birds, and provides vital information for conservation planning. We evaluated and compared nest-site selection and breeding success of Vermilion Flycatchers (VEFL) and Fork-tailed Flycatchers (FTFL) in areas with and without livestock in the Espinal biome of La Pampa Province, Argentina. VEFL selected nest sites with greater tree cover, whereas FTFL nested in taller trees with narrower trunks. We found a weak positive effect of nest height, diameter of nest-support branches and the absence of livestock on VEFL nest survival, and a weak positive effect of nest orientation on FTFL nest survival. However, although some habitat characteristics varied between the two areas, nest site characteristics of both species in areas with and without livestock did not differ significantly. The nest survival was 12.7% for VEFL and 28.7% for FTFL, and did not differ significantly between these two flycatchers. The breeding ecology of these birds has likely been molded by a broad suite of selective pressures, such as severe weather, brood parasites and predators that characterize habitats in central Argentina.

中文翻译：

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半干旱森林中两种新热带南方候鸟的巢址选择和繁殖成功：有和没有牲畜的地点比较

摘要 了解支持巢址选择的机制提供了关于塑造鸟类繁殖生态的选择力的新见解，并为保护规划提供了重要信息。我们评估并比较了阿根廷拉潘帕省 Espinal 生物群落有和没有牲畜的地区，朱红色鹟 (VEFL) 和叉尾鹟 (FTFL) 的巢址选择和繁殖成功。VEFL 选择树木覆盖较大的筑巢地点，而 FTFL 筑巢在树干较窄的较高树木中。我们发现巢高度、巢支撑分支的直径和家畜的缺乏对 VEFL 巢存活率的微弱积极影响，以及巢方向对 FTFL 巢生存的微弱积极影响。然而，虽然这两个地区的一些栖息地特征有所不同，在有牲畜和没有牲畜的地区，这两种物种的筑巢地点特征没有显着差异。VEFL 的巢存活率为 12.7%，FTFL 为 28.7%，这两种捕蝇器之间没有显着差异。这些鸟类的繁殖生态可能受到一系列选择压力的影响，例如阿根廷中部栖息地的恶劣天气、寄生虫和捕食者。