Low-temperature nights delay the timing of breeding in a wild songbird

Global climate change has posed widespread challenges to the ecological process critical to the fitness of many wild organisms, such as reproductive phenology. Many bird species have advanced their reproductive phenology in response to the increases in spring temperatures. However, the mechanism of how climate influences the timing of breeding is still often unclear in many species. We explored the relationship between the timing of breeding and spring temperatures based on 14 years of data on Hair-Crested Drongos (Dicrurus hottentottus) in the wild. By applying a ‘sliding window’ approach, we aimed to identify the time window and weather variable that best explains the timing of breeding at both population and individual levels. We found that the more nights with a minimum temperature below 17℃, around three weeks earlier than the peak reproduction, delayed the breeding time. Low night temperatures may force females to allocate more energy to thermoregulation and therefore physiologica..., Nests were systematically searched from the entire study area in each season. Once located, we visited each nest regularly, usually every 1–3 days, for recording the laying date (i.e. the date of the first egg in each clutch). Females lay one egg per day until the clutch is full. Clutch size ranges from 2 to 5, with the mode at 4 eggs. Adult Drongos were captured by mist-netting, either during the incubation or nestling provisioning periods near their nesting trees. Captured adults were marked with a metal ring and a unique combination of colour rings. Adults were sexed based on the size of their brood patches: Females have much larger brood patches than males. We placed high-resolution video cameras (Sony HDR-160E or HDR-260E) at around 20 meters from the nest to determine the identity of the adults. None of the nests were abandoned because of the monitoring.,

全球气候变化已对诸多野生生物生存至关重要的生态过程（如繁殖物候）造成广泛挑战。诸多鸟类为响应春季气温升高，已提前自身繁殖物候。然而，多数物种中气候如何影响繁殖时间的机制仍往往不甚明晰。本研究基于14年间针对野生发冠卷尾（Hair-Crested Drongos, Dicrurus hottentottus）的野外观测数据，探索了繁殖时间与春季气温之间的关联。我们采用「滑动窗口（sliding window）」分析法，旨在确定在种群及个体水平上最能解释繁殖时间的时间窗口与气象变量。研究发现，在繁殖高峰前三周左右，最低气温低于17℃的夜晚数量越多，繁殖启动时间越晚。夜间低温可能迫使雌性投入更多能量用于体温调节，进而在生理上……每个季节均会对整个研究区域开展系统性鸟巢搜寻。一旦定位到鸟巢，我们便会定期（通常每1至3天）前往探访，记录产卵日期（即每窝首枚卵的产出日期）。雌性每日产卵一枚，直至窝卵数达到饱和。窝卵数范围为2至5枚，众数为4枚。成鸟可通过雾网法在孵化期或育雏期的巢树附近捕获，为其佩戴金属环与独特配色的彩色脚环组合。通过育斑大小进行性别鉴定：雌性的育斑远大于雄性。我们在距巢约20米处放置高分辨率摄像机（索尼HDR-160E或HDR-260E），以确定成鸟的身份。所有巢均未因监测活动而遭到弃置。