Breeding timed to match optimal resource abundance is vital for the successful reproduction of species, and breeding is therefore sensitive to environmental cues. As the timing of breeding shifts with a changing climate, this may not only affect the onset of breeding but also its termination, and thus the length of the breeding period. We use an extensive dataset of over 820K nesting records of 73 bird species across the boreal region in Finland to probe for changes in the beginning, end, and duration of the breeding period over four decades (1975 to 2017). We uncover a general advance of breeding with a strong phylogenetic signal but no systematic variation over space. Additionally, 31% of species contracted their breeding period in at least one bioclimatic zone, as the end of the breeding period advanced more than the beginning. We did not detect a statistical difference in phenological responses of species with combinations of different migratory strategy or number of broods. Nonetheless, we find systematic differences in species responses, as the contraction in the breeding period was found almost exclusively in resident and short-distance migrating species, which generally breed early in the season. Overall, changes in the timing and duration of reproduction may potentially lead to more broods co-occurring in the early breeding season—a critical time for species’ reproductive success. Our findings highlight the importance of quantifying phenological change across species and over the entire season to reveal shifts in the community-level distribution of bird reproduction.

定时进行匹配最佳资源丰度的育种对于物种的成功繁殖至关重要，因此育种对环境线索十分敏感。随着繁殖时间随气候变化而变化，这不仅可能影响繁殖的开始，而且会影响其终止，进而影响繁殖期的长短。我们使用广泛的数据集，涵盖芬兰北方地区73种鸟类的超过820K的筑巢记录，以探索四个十年（1975年至2017年）的繁殖期开始，结束和持续时间的变化。我们揭示了具有强系统发生信号但在空间上没有系统变化的育种的一般进展。此外，由于育种期结束比开始时提前，因此有31％的物种在至少一个生物气候带收缩了繁殖期。我们没有发现具有不同迁徙策略或育雏数量的物种在物候响应上的统计学差异。尽管如此，我们发现物种反应的系统性差异，因为在繁殖期的收缩几乎只在常驻和短距离迁徙物种中发现，这些物种通常在本季节早期繁殖。总体而言，繁殖时间和持续时间的改变可能潜在地导致在繁殖的早期共同繁殖更多的亲鱼，这是物种繁殖成功的关键时期。我们的研究结果突出了量化物种间和整个季节的物候变化对揭示鸟类繁殖的社区水平分布变化的重要性。