Urbanization is increasing at a rapid pace globally. Understanding the links among environmental characteristics, phenotypes, and fitness enables researchers to predict the impact of changing landscapes on individuals and populations. Although avian reproductive output is typically lower in urban compared with natural areas, the underlying reasons for this discrepancy may lie at the intersection of abiotic and biotic environmental and individual differences. Recent advances in urban ecology highlight the effect of heavy metal contamination on stress physiology. As high levels of glucocorticoid hormones decrease parental investment, these hormones might be the link to decreased reproductive success in areas of high environmental pollution. In this study, we aimed to identify which abiotic stressors are linked to avian reproductive output in urban areas and whether this link is mediated by individual hormone levels. We used fine-scaled estimates (2 m² spatial resolution) of nighttime light, noise, and urban density to assess their impacts on the physiological condition of adult house sparrows (Passer domesticus). We measured circulating levels of lead and glucocorticoid concentrations in 40 breeding pairs of free-living house sparrows and related these physiological traits to reproductive success. Using structural equation modeling, we found that increased urban density levels linked directly to increased plasma corticosterone and lead concentrations that subsequently led to decreased fledgling mass. Sparrows with increased lead concentrations in plasma also had higher corticosterone levels. Although urban areas may be attractive due to decreased natural predators and available nesting sites, they may act as ecological traps that increase physiological damage and decrease fitness. To illustrate, avian development is strongly explained by parental corticosterone levels, which vary significantly in response to urban density and lead pollution. With fine-scale ecological mapping for a species with small home ranges, we demonstrated the presence and impacts of urban stressors in a small city with high human densities.

中文翻译：

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铅和糖皮质激素浓度的增加会降低城市梯度沿线家麻雀的繁殖成功率

全球城市化进程正在快速推进。了解环境特征、表型和适应性之间的联系，使研究人员能够预测不断变化的景观对个体和种群的影响。尽管与自然地区相比，城市的鸟类繁殖产量通常较低，但造成这种差异的根本原因可能在于非生物和生物环境以及个体差异的交叉点。城市生态学的最新进展突出了重金属污染对应激生理学的影响。由于高水平的糖皮质激素减少了父母的投资，这些激素可能与高环境污染地区的繁殖成功率下降有关。在这项研究中，我们的目的是确定哪些非生物压力因素与城市地区的鸟类繁殖产出有关，以及这种联系是否由个体激素水平介导。我们使用精细尺度估计（2 m²空间分辨率）的夜间光线、噪音和城市密度，以评估它们对成年家麻雀（Passer domesticus ）生理状况的影响). 我们测量了 40 对自由生活家麻雀的循环铅浓度和糖皮质激素浓度，并将这些生理特征与繁殖成功相关联。使用结构方程模型，我们发现城市密度水平的增加与血浆皮质酮和铅浓度的增加直接相关，这些浓度随后导致雏鸟质量下降。血浆中铅浓度增加的麻雀也有更高的皮质酮水平。尽管由于天敌减少和可用的筑巢地点，城市地区可能很有吸引力，但它们可能会成为增加生理损伤和降低适应性的生态陷阱。举例说明，亲代皮质酮水平强烈地解释了鸟类的发育，皮质酮水平因城市密度和铅污染而显着不同。