Department of Forest and Wildlife Ecology, University of Wisconsin-Madison, Madison, WI, 53706, USA.
Glob Chang Biol. 2015 Feb;21(2):572-85. doi: 10.1111/gcb.12740. Epub 2014 Oct 16.
Much of the recent changes in North American climate have occurred during the winter months, and as result, overwintering birds represent important sentinels of anthropogenic climate change. While there is mounting evidence that bird populations are responding to a warming climate (e.g., poleward shifts) questions remain as to whether these species-specific responses are resulting in community-wide changes. Here, we test the hypothesis that a changing winter climate should favor the formation of winter bird communities dominated by warm-adapted species. To do this, we quantified changes in community composition using a functional index--the Community Temperature Index (CTI)--which measures the balance between low- and high-temperature dwelling species in a community. Using data from Project FeederWatch, an international citizen science program, we quantified spatiotemporal changes in winter bird communities (n = 38 bird species) across eastern North America and tested the influence of changes in winter minimum temperature over a 22-year period. We implemented a jackknife analysis to identify those species most influential in driving changes at the community level and the population dynamics (e.g., extinction or colonization) responsible for these community changes. Since 1990, we found that the winter bird community structure has changed with communities increasingly composed of warm-adapted species. This reshuffling of winter bird communities was strongest in southerly latitudes and driven primarily by local increases in abundance and regional patterns of colonization by southerly birds. CTI tracked patterns of changing winter temperature at different temporal scales ranging from 1 to 35 years. We conclude that a shifting winter climate has provided an opportunity for smaller, southerly distributed species to colonize new regions and promote the formation of unique winter bird assemblages throughout eastern North America.
近年来，北美气候的许多变化发生在冬季，因此，越冬鸟类是人为气候变化的重要哨兵。虽然越来越多的证据表明鸟类种群正在对变暖的气候做出反应（例如，向极地转移），但这些物种特异性的反应是否导致群落范围的变化仍存在疑问。在这里，我们检验了一个假设，即不断变化的冬季气候应该有利于形成以温暖适应物种为主的冬季鸟类群落。为此，我们使用功能指数——群落温度指数（CTI）——来量化群落组成的变化，该指数衡量了群落中低温和高温栖息物种之间的平衡。我们利用国际公民科学项目“喂鸟器观察计划”的数据，量化了整个北美东部冬季鸟类群落的时空变化（n = 38 种鸟类），并检验了 22 年来冬季最低温度变化对群落的影响。我们采用了刀切分析来确定在群落水平上最具影响力的物种以及导致这些群落变化的种群动态（例如灭绝或殖民化）。自 1990 年以来，我们发现冬季鸟类群落结构发生了变化，越来越多的温暖适应物种组成了群落。这种冬季鸟类群落的改组在较温暖的纬度地区最为强烈，主要是由于当地丰度的增加和南部鸟类的区域殖民化模式。CTI 在从 1 年到 35 年的不同时间尺度上追踪了不断变化的冬季温度模式。我们得出结论，不断变化的冬季气候为较小、分布在较温暖地区的物种提供了机会，使其能够在新的地区殖民，并促进整个北美东部独特的冬季鸟类组合的形成。
