AimSeasonality governs species composition at a given place and time. However, the effects of climate and land‐use change can vary by season, altering species composition. These changes can lead to a loss of distinct seasonal community composition, representing a novel form of biotic homogenisation. We ask if breeding and winter bird communities are becoming more similar over time. If so, is homogenisation occurring more rapidly in winter than in the breeding season, and has the presence of individual species changed between seasons?LocationNortheastern United States.Time Period1989–2019.Major Taxa StudiedTwo hundred thirty‐eight bird species.MethodsWe use data from The National Audubon Society's Christmas Bird Count and the North American Breeding Bird Survey to test if winter and breeding bird communities have become more similar (homogenised). We evaluate this change using the Sørensen dissimilarity index, and its components of turnover (species replacement) and nestedness (a subset of a more species rich community) and describe the mechanism in which the seasonal winter and breeding bird communities are changing.ResultsWe found that winter and breeding bird communities are homogenising, driven by significant decrease in turnover and a marginal decrease nestedness. When viewing breeding and wintering communities separately, we observe different trends. Breeding communities are becoming more unique with decreasing turnover and nestedness. Winter communities are becoming more similar to each other, with decreasing turnover and nestedness. More breeding species are declining and species that are typically found in the winter and year‐round residents are the main contributors to the homogenisation between seasons.Main ConclusionsWe show for the first time homogenisation between winter and breeding bird communities over time across the northeastern United States. This insight into how individual species are faring between seasons, and how they impact community structure, can be used when implementing conservation measures for maintaining ecological functioning and integrity.

中文翻译：

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鸟类群落季节性的侵蚀


目的季节性控制特定地点和时间的物种组成。然而，气候和土地利用变化的影响可能因季节而异，从而改变物种组成。这些变化可能导致独特的季节性群落组成的丧失，代表了一种新的生物同质化形式。我们询问繁殖和冬季鸟类群落是否随着时间的推移变得越来越相似。如果是这样，同质化在冬季发生的速度是否比繁殖季节更快，并且各个物种的存在在季节之间是否发生变化？位置美国东北部。时间段 1989-2019。主要分类单元研究了 238 种鸟类。方法我们使用来自国家奥杜邦协会的圣诞节鸟类计数和北美繁殖鸟类调查，以测试冬季和繁殖鸟类群落是否变得更加相似（同质化）。我们使用 Sørensen 相异性指数及其周转（物种替换）和嵌套（物种更丰富的群落的子集）组成部分来评估这种变化，并描述季节性冬季和繁殖鸟类群落变化的机制。结果我们发现由于周转率显着下降和筑巢量略有减少，冬季和繁殖鸟类群落正在同质化。当分别观察繁殖群落和越冬群落时，我们观察到不同的趋势。随着周转和嵌套的减少，繁殖群落变得更加独特。冬季群落彼此变得更加相似，周转率和嵌套度不断减少。更多的繁殖物种正在减少，通常在冬季和常年栖息的物种是季节间同质化的主要贡献者。主要结论我们首次展示了美国东北部冬季鸟类群落和繁殖鸟类群落之间随着时间的推移的同质化。在实施维持生态功能和完整性的保护措施时，可以利用对各个物种在季节之间的生存情况及其如何影响群落结构的深入了解。