Predator fear effects influence reproductive outcomes in many species. In non-urban systems, passerines often respond to predator cues by reducing parental investment, resulting in smaller and lighter nestlings. Since trophic interactions in urban areas are highly altered, it is unclear how passerines respond to fear effects in human-altered landscapes. Nestlings of passerines in urban areas also tend to be smaller and lighter than their rural counterparts and are often exposed to high densities of potential predators yet experience lower per capita predation—the predation paradox. We suggest fear effects in urban habitats could be a significant mechanism influencing nestling condition in birds, despite lowered predation rates. We manipulated exposure of nesting birds to adult-consuming predator risk in residential yards across a gradient of urbanization to determine the relative influence of urbanization and fear on nestling condition. We found nestlings had reduced mass in nests exposed to predator playbacks as well as in more urban areas. Despite lower per capita predation rates in urban areas, fear effects from increased predator densities may influence passerine fitness through reduced nestling condition. As urban development expands, biodiversity conservation hinges on a deeper mechanistic understanding of how urbanization affects reproductive outcomes.

中文翻译：

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危险的选择：对成年鸟类的恐惧景观减少了城市梯度上的雏鸟条件

捕食者恐惧效应影响许多物种的生殖结果。在非城市系统中，雀鸟通常通过减少父母的投资来响应捕食者的线索，从而产生更小更轻的雏鸟。由于城市地区的营养相互作用发生了很大变化，目前尚不清楚雀鸟如何应对人类改变的景观中的恐惧效应。城市地区的雀鸟雏鸟也往往比农村小鸟更小、更轻，并且经常暴露于高密度的潜在捕食者，但人均捕食量较低——捕食悖论。我们认为，尽管捕食率降低，但城市栖息地的恐惧效应可能是影响鸟类筑巢条件的重要机制。我们操纵了筑巢鸟类在城市化梯度中住宅院子中成年捕食者风险的暴露，以确定城市化和恐惧对雏鸟状况的相对影响。我们发现雏鸟在暴露于捕食者回放的巢穴中以及在更多的城市地区减少了质量。尽管城市地区的人均捕食率较低，但捕食者密度增加带来的恐惧效应可能会通过降低雏鸟条件来影响雀鸟的健康。随着城市发展的扩大，生物多样性保护取决于对城市化如何影响生殖结果的更深入的机制理解。尽管城市地区的人均捕食率较低，但捕食者密度增加引起的恐惧效应可能会通过降低雏鸟条件来影响雀鸟的健康。随着城市发展的扩大，生物多样性保护取决于对城市化如何影响生殖结果的更深入的机制理解。尽管城市地区的人均捕食率较低，但捕食者密度增加带来的恐惧效应可能会通过降低雏鸟条件来影响雀鸟的健康。随着城市发展的扩大，生物多样性保护取决于对城市化如何影响生殖结果的更深入的机制理解。