Data_Sheet_1_Extreme Hot Weather Has Stronger Impacts on Avian Reproduction in Forests Than in Cities.pdf

Climate change and urbanisation are among the most salient human-induced changes affecting Earth’s biota. Extreme weather events can have high biological impacts and are becoming more frequent recently. In cities, the urban heat island can amplify the intensity and frequency of hot weather events. However, the joint effects of heat events and urban microclimate on wildlife are unclear, as urban populations may either suffer more from increased heat stress or may adapt to tolerate warmer temperatures. Here, we test whether the effects of hot weather on reproductive success of great tits (Parus major) are exacerbated or dampened in urban environments compared to forest habitats. By studying 760 broods from two urban and two forest populations over 6 years, we show that 14–16 days-old nestlings have smaller body mass and tarsus length, and suffer increased mortality when they experience a higher number of hot days during the nestling period. The negative effects of hot weather on body mass and survival are significantly stronger in forests than in urban areas, where these effects are dampened or even reversed. These results suggest that urban nestlings are less vulnerable to extreme hot weather conditions than their non-urban conspecifics. This difference might be the result of adaptations that facilitate heat dissipation, including smaller body size, altered plumage and reduced brood size. Alternatively or additionally, parental provisioning and food availability may be less affected by heat in urban areas. Our findings suggest that adaptation to heat stress may help birds cope with the joint challenges of climate change and urbanisation.

气候变化与城市化是影响地球生物区系的两类最显著的人为驱动环境变化。极端天气事件可产生强烈的生物学效应，且近年来发生频率持续攀升。在城市区域，城市热岛效应（Urban Heat Island）会加剧高温天气事件的强度与发生频次。然而，高温事件与城市微气候对野生生物的联合效应尚未明确：城市种群或因热胁迫加剧承受更严重的负面影响，或已演化出适应更高温环境的耐受能力。本研究以大山雀（Parus major）为研究对象，旨在探究相较于森林生境，高温天气对其繁殖成功率的影响在城市环境中是被加剧还是被缓解。本研究历时6年，对2个城市种群与2个森林种群的760窝雏鸟开展观测，结果显示：若雏鸟在育雏期经历更多高温天数，则14~16日龄雏鸟的体重与跗跖长度均更小，且死亡率显著升高。高温天气对雏鸟体重与存活的负面影响在森林生境中显著强于城市区域：在城市环境中，此类负面影响被缓解甚至完全逆转。上述结果表明，相较于非城市环境中的同种个体，城市雏鸟对极端高温环境的耐受性更强。这种差异可能源于促进热散失的适应性演化，包括体型更小、羽毛特征改变以及窝雏数减少。此外，城市区域的亲鸟育雏行为与食物可获得性或许受高温影响更小。本研究结果表明，对热胁迫的适应性演化或可帮助鸟类应对气候变化与城市化带来的双重挑战。