Data from: Increasing temperature, not mean temperature, is a cue for avian timing of reproduction

Timing of reproduction in temperate zone birds is strongly correlated with spring temperature, with an earlier onset of breeding in warmer years. Females adjust their laying between years to be synchronized with local food sources and thereby optimize reproductive output. However, climate change currently disrupts the link between predictive environmental cues and spring phenology. To investigate direct effects of temperature on the decision to lay, and its genetic basis, we used pairs of Great Tits (Parus major) with known ancestry and exposed them to simulated spring scenarios in climate-controlled aviaries. In each of three years, we exposed birds to different patterns of changing temperature. We varied the timing of a temperature change, the daily temperature amplitude and the onset and speed of a seasonal temperature rise. We show that females fine-tune their laying in response to a seasonal increase in temperature, whereas mean temperature and daily temperature variation alone do not affect laying dates. Luteinizing hormone concentrations and gonadal growth in early spring were not influenced by temperature or temperature rise, possibly posing a constraint to an advancement of breeding. Similarities between sisters in their laying dates indicate genetic variation in cue sensitivity. These results refine our understanding of how changes in spring climate might affect the mismatch in avian timing and thereby population viability.

温带鸟类的繁殖时机与春季气温呈显著相关，在更温暖的年份，其繁殖启动时间更早。雌鸟会在不同年份调整产卵时间，以匹配当地食物资源的周期，进而优化繁殖产出。然而，当前的气候变化正打破了预测性环境线索与春季物候之间的关联。为探究气温对产卵决策的直接影响及其遗传基础，我们选取了血统已知的大山雀（Great Tits, *Parus major*）成对个体，将其置于可控气候鸟舍中，并模拟春季环境场景。在连续三年的实验中，我们让鸟群暴露于不同变化模式的气温条件下：调整气温变化的时机、每日气温振幅，以及季节性升温的起始时间与速率。研究结果表明，雌鸟会根据季节性升温微调产卵时间，而仅靠平均气温或单日气温波动则不会对产卵日期产生影响。早春时节的黄体生成素（Luteinizing hormone）浓度与性腺发育（gonadal growth）并未受到气温或季节性升温的影响，这可能会对繁殖提前形成一定限制。同窝雌性个体在产卵日期上的相似性，表明雌鸟对环境线索的敏感度存在遗传变异。本研究结果完善了我们对春季气候变化如何引发鸟类繁殖物候错配，进而影响种群存续能力的认知。