Data from: A migratory northern ungulate in the pursuit of spring: jumping or surfing the green wave?

The Forage Maturation Hypothesis (FMH) states that herbivores migrate along a phenological gradient of plant development in order to maximize energy intake. Despite strong support for the FMH, the actual relationship between plant phenology and ungulate movement has remained enigmatic. We linked plant phenology (MODIS-NDVI) and space use of 167 migratory and 78 resident red deer (Cervus elaphus) using a space-time-time matrix of "springness", defined as the instantaneous rate of green-up (IRG). Consistent with the FMH, migrants experienced substantially greater access to early plant phenology than residents. Deer were also more likely to migrate in areas where migration led to greater gains in springness. Rather than "surfing the green wave" during migration, migratory red deer moved rapidly from the winter to the summer range, thereby "jumping the green wave". However, migrants, and to a lesser degree residents, did track phenological green-up through parts of the growing season by making smaller-scale adjustments in habitat use. We conclude that, whereas in some systems migration itself is a way to surf the green wave, in others it may simply be a means to re-connect with phenological spring at the summer range.

食物成熟假说（Forage Maturation Hypothesis, FMH）提出，草食动物会沿植物发育的物候梯度迁徙，以最大化自身能量摄入。尽管该假说已获得诸多实证支持，但植物物候与有蹄类动物移动之间的实际关联始终不明朗。我们通过以“返青度”——定义为瞬时返青速率（instantaneous rate of green-up, IRG）——构建的时空矩阵，将植物物候数据（中分辨率成像光谱仪归一化植被指数，MODIS-NDVI）与167只迁徙马鹿（Cervus elaphus）及78只居留马鹿的空间利用情况进行了关联分析。与该假说的预测一致，迁徙个体相较居留个体，能够更早接触到处于发育早期的植物。鹿群更倾向于在迁徙可带来更高返青度增益的区域开展迁徙活动。与“追随绿波”的迁徙模式不同，迁徙马鹿会快速从越冬栖息地转移至夏居栖息地，实则“跨越了绿波”。不过，迁徙个体以及程度较轻的居留个体，会通过小尺度调整栖息地利用策略，在生长季的部分时段追踪物候返青进程。我们最终得出结论：在部分生态系统中，迁徙本身就是一种追随绿波的方式；而在另一些生态系统中，迁徙或许仅仅是为了在夏居栖息地重新对接物候意义上的春季。