Data from: Hidden survival heterogeneity of three common eider populations in response to climate fluctuations

(1) Understanding how individuals and populations respond to fluctuations in climatic conditions is critical to explain and anticipate changes in ecological systems. Most such studies focus on climate impacts on single populations without considering inter- and intra-population heterogeneity. However, comparing geographically dispersed populations limits the risk of faulty generalizations and helps to improve ecological and demographic models. (2) We aimed to determine whether differences in migration tactics among and within populations would induce inter- or intra-population heterogeneity in survival in relation to winter climate fluctuations. Our study species was the Common eider (Somateria mollissima), a marine duck with a circumpolar distribution, which is strongly affected by climatic conditions during several phases of its annual cycle. (3) Capture-mark-recapture (CMR) data were collected in two arctic (northern Canada and Svalbard) and one subarctic (northern Norway) population over a period of 18, 15 and 29 years, respectively. These three populations have different migration tactics and experience different winter climatic conditions. Using multi-event and mixture modelling, we assessed the association between adult female eider survival and winter conditions as measured by the North Atlantic Oscillation index. (4) We found that winter weather conditions affected survival of female eiders from each of these three populations. However, different mechanisms seemed to be involved. Survival of the two migrating arctic populations was impacted directly by changes in the NAO, whereas the subarctic resident population was affected by the NAO with time lags of two to three years. Moreover, we found evidence for intra-population heterogeneity in the survival response to the winter NAO in the Canadian eider population, where individuals migrate to distinct wintering areas. (5) Our results illustrate how individuals and populations of the same species can vary in their responses to climate variation. We suspect that the found variation in survival response of birds to winter conditions is partly explained by differences in migration tactic. Detecting and accounting for inter- and intra-population heterogeneity will improve our predictions concerning the response of wildlife to global changes.

(1) 理解个体与种群对气候波动的响应机制，是解释并预测生态系统变化的关键所在。现有此类研究大多聚焦气候对单一种群的影响，却未考虑种群间及种群内部的异质性。然而，对比地理分布分散的多个种群，可降低错误泛化的风险，同时有助于优化生态与种群统计模型。(2) 本研究旨在探究种群间与种群内部的迁徙策略差异，是否会引发越冬气候波动相关的存活率种群间及种群内部异质性。研究物种为普通绒鸭（Somateria mollissima），这是一种环极分布的海鸭，其年生活史的多个阶段均会受到气候条件的显著影响。(3) 研究采集了标记重捕（Capture-mark-recapture, CMR）数据，分别来自两个北极种群（加拿大北部与斯瓦尔巴群岛）以及一个亚北极种群（挪威北部），对应的监测时长分别为18年、15年与29年。这三个种群具备不同的迁徙策略，且经历的越冬气候条件存在差异。本研究采用多事件与混合模型，以北大西洋涛动（North Atlantic Oscillation, NAO）指数为衡量指标，评估了成年雌性绒鸭存活率与冬季气候条件之间的关联。(4) 研究发现，冬季气候条件会对这三个种群的雌性绒鸭存活率产生影响，但背后的作用机制各不相同。两个迁徙型北极种群的存活率直接受北大西洋涛动变化的调控，而亚北极居留型种群的存活率则会受到滞后2至3年的北大西洋涛动影响。此外，在加拿大绒鸭种群中，我们发现了存活率对冬季北大西洋涛动响应的种群内部异质性证据——该种群的个体会迁徙至不同的越冬区域。(5) 本研究结果阐明了同一物种的不同个体与种群，对气候变异的响应模式存在差异。我们推测，鸟类越冬存活率响应的差异，部分可由迁徙策略的不同来解释。探明并纳入种群间与种群内部的异质性，将有助于提升我们对野生动物响应全球变化的预测能力。