Centre for Ecological and Evolutionary Synthesis (CEES), Department of Biosciences, University of Oslo, P.O. Box 1066 Blindern, NO-0316, Oslo, Norway.
The Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences, P.O. Box 5003, NO-1432, Aas, Norway.
Ecology. 2016 Apr;97(4):1058-1068. doi: 10.1890/15-1191.1.
Autumn has to a large extent been neglected in the climate effect literature, yet autumn events, e.g., plant senescence and animal migration, affect fitness of animals differently than spring events. Understanding how variables including plant phenology influence timing of autumn migrations is important to gain a comprehensive understanding of the full annual cycle of migratory species. Here we use 13 yr of data from 60 male and 168 female red deer (Cervus elaphus) to identify triggers of autumn migration. We relate the timing of autumn migration to environmental variables like snow fall, temperature, and plant phenology (NDVI), and to onset of hunting, sex, and migration distance. Severe weather has been suggested as the main trigger of autumn migration, but we found that the majority of the individuals had left the summer range well before snow fall (80.3%) and frost (70.5%), and also before the peak deterioration in forage quality (71.9%). Declining temperatures were associated with a higher daily migration potential. Onset of hunting showed the largest effect on migration potential, with a marked increase during the first days of hunting. Individuals still present in the summer range when snow fall, frost, or peak forage deterioration occurred showed a significantly higher migration potential around these events. Males were less responsive to environmental cues, suggesting rutting activity, starting earlier in males, initiate movement prior to such conditions. Also, individuals with longer migration distances had a higher migration potential late in the season than individuals with shorter migration distances. Our study shows that factors beyond weather and plant phenology, such as onset of hunting, may be important triggers of autumn migration. Severe weather and forage deterioration were important triggers for the individuals experiencing this, which suggests a hierarchical response to environmental cues. The trade-off between staying longer in the summer range and increased energy expenditures if surprised by severe weather is asymmetric, and leaving well in advance can be seen as a risk-averse tactic.
秋季在气候效应文献中很大程度上被忽视了，但秋季事件，如植物衰老和动物迁徙，会对动物的适应力产生不同于春季事件的影响。了解包括植物物候在内的变量如何影响秋季迁徙的时间，对于全面了解迁徙物种的完整年度周期非常重要。在这里，我们使用了 60 只雄性和 168 只雌性红鹿（ Cervus elaphus ） 13 年的数据来确定秋季迁徙的触发因素。我们将秋季迁徙的时间与环境变量（如降雪、温度和植物物候（NDVI））以及狩猎开始、性别和迁徙距离联系起来。恶劣天气被认为是秋季迁徙的主要触发因素，但我们发现大多数个体在降雪（80.3%）和霜冻（70.5%）之前，以及在饲料质量恶化的高峰期（71.9%）之前，就已经离开了夏季栖息地。温度下降与更高的每日迁徙潜力有关。狩猎的开始对迁徙潜力的影响最大，在狩猎的最初几天，这种影响显著增加。当降雪、霜冻或饲料质量高峰期发生时仍留在夏季栖息地的个体，在这些事件发生前后，迁徙潜力明显更高。雄性对环境线索的反应较小，这表明，雄性的发情活动开始得更早，会在这些条件出现之前就开始移动。此外，迁徙距离较长的个体在赛季后期的迁徙潜力高于迁徙距离较短的个体。我们的研究表明，除了天气和植物物候之外，狩猎的开始等因素可能是秋季迁徙的重要触发因素。恶劣天气和饲料恶化是经历这些事件的个体的重要触发因素，这表明对环境线索的反应是分层次的。在夏季栖息地停留更长时间和因恶劣天气而增加能源支出之间的权衡是不对称的，提前离开可以被视为一种避险策略。
