Linking Mule Deer Migration to Spring Green-Up in Wyoming

Each year, plants and animals undergo certain life cycle events, such as breeding or flowering. These phenological events are linked to weather and climate, and as temperature and precipitation patterns have changed, some spring events are occurring earlier. These changes in plant phenology can have cascading effects on wildlife such as elk, moose, and mule deer, which depend on plants for food. It’s thought that the quality of forage available in the spring could play a critical role for these big game species, which need to replenish energy depleted during the winter, in order to survive and successfully reproduce. Climate change will alter plant phenology, which in turn is likely to effect when, where, and for how long big game species can access the best quality food.
 
In mountainous areas, spring green-up occurs in a wave, beginning first at lower elevations before reaching higher elevations. Thus, to extend the amount of time that individuals are exposed to the highest quality food, they should follow this wave of spring green-up. The goal of this project is to determine whether mule deer track the spring green-up of vegetation as they migrate from their low elevation winter range to their high elevation summer range. While it’s been hypothesized that mule deer and other herbivores “surf the green wave” – or track spring green-up – the question remains as to whether this behavior occurs or is common among big game species. To answer this question, researchers are tracking the movements of mule deer in Wyoming and are matching the progression of the green wave using GPS telemetry and remote-sensing technology.
 
So far, researchers have found that migratory mule deer do in fact surf the green wave. This result indicates that migratory routes are more than just a link between seasonal ranges; rather, they represent an important source of high-quality vegetation that mule deer can access by carefully timing their movements during spring migration. This means that changes in plant phenology resulting from shifting climate conditions could pose a threat to big game species like mule deer, potentially altering the quality and quantity of forage obtained during migration.