In northern climates, spring is a time of rapid environmental change: for migrating terrestrial animals, melting snow facilitates foraging and travel, and newly-emergent vegetation provides a valuable nutritional resource. These changes result in selection on the timing of important life-history events such as migration and parturition occurring when high-quality resources are most abundant. We examined the timing of female caribou (Rangifer tarandus, n = 94) migration and parturition in five herds across seven years in Newfoundland, Canada as a function of two measures of environmental change-snowmelt and vegetation green-up. We generated resource selection functions to test whether caribou selected for areas associated with snowmelt and green-up during migration and following calving. We found that caribou migrated approximately one week prior to snowmelt, with the flush of emergent vegetation occurring during the weeks following parturition. The results indicate that caribou "jump" the green wave of emergent forage and do so by tracking the receding edge of melting snow, likely reducing movement and foraging costs related to snow cover. Our research further broadens the ecological scope of resource tracking in animals. We demonstrate that resource tracking extends beyond resources directly related to foraging to those related to movement. We also show that snowmelt provides an environmental cue that may provide a buffer against changing environmental conditions.

中文翻译：

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追踪融雪以跳过绿波：北方有蹄类动物迁徙的物候驱动因素

在北方气候中，春季是环境快速变化的时期：对于陆生动物的迁徙，融雪有利于觅食和旅行，而新出现的植被则提供了宝贵的营养资源。这些变化导致对重要生命历史事件的时间选择，例如在高质量资源最丰富时发生的迁移和分娩。我们研究了加拿大纽芬兰七年间五群雌性驯鹿（Rangifer tarandus，n = 94）迁徙和分娩的时间，作为两种环境变化指标 - 融雪和植被绿化的函数。我们生成了资源选择函数来测试驯鹿是否选择了在迁徙和产犊后与融雪和绿化相关的区域。我们发现驯鹿大约在融雪前一周迁徙，在分娩后的几周内出现了涌现的植被。结果表明，北美驯鹿通过追踪融雪的后退边缘来“跳跃”紧急觅食的绿色浪潮，这样做可能会减少与积雪有关的移动和觅食成本。我们的研究进一步拓宽了动物资源追踪的生态范围。我们证明，资源跟踪从与觅食直接相关的资源扩展到与移动相关的资源。我们还表明，融雪提供了一种环境线索，可以为不断变化的环境条件提供缓冲。草料的绿色浪潮，并通过跟踪融雪的后退边缘来做到这一点，可能会减少与积雪有关的移动和觅食成本。我们的研究进一步拓宽了动物资源追踪的生态范围。我们证明，资源跟踪从与觅食直接相关的资源扩展到与移动相关的资源。我们还表明，融雪提供了一种环境线索，可以为不断变化的环境条件提供缓冲。草料的绿色浪潮，并通过跟踪融化的雪的后退边缘来做到这一点，可能会减少与积雪有关的移动和觅食成本。我们的研究进一步拓宽了动物资源追踪的生态范围。我们证明，资源跟踪从与觅食直接相关的资源扩展到与移动相关的资源。我们还表明，融雪提供了一种环境线索，可以为不断变化的环境条件提供缓冲。