Energy development disrupts mule deer migration

Each year, mule deer migrate in the American West to follow the green-up of plants as they sprout at various elevations – a phenomenon biologists call “surfing the green wave.” The deer rely on this surfing behavior to find the freshest and most nutritious plants that help them recover from winter and put on fat in preparation for the next lean season. However, according to a new study led by the University of Wyoming (UW) in collaboration with the U.S. Geological Survey (USGS), when energy development disrupts their migration corridors, deer often lose their ability of foraging with the wave of the most nutritious springtime plants.

“Mule deer are known for how precisely they match their movements with spring green-up, so this result was particularly striking,” said study lead author Ellen Aikens, a UW PhD graduate, currently working at the USGS South Dakota Cooperative Fish and Wildlife Research Unit. “The gas wells caused them to let the best food of the year slip away from them.”

The researchers followed a herd of migratory deer that winters in sagebrush basins and summers in the Sierra Madre Mountains for 14 years. During this period, dozens of new wells were drilled for coalbed methane extraction in the middle of a deer corridor. The analysis revealed that, as development intensity increased over time, the deer began to “hold up” when reaching natural gas wells, pausing their spring migration, and letting the wave of green vegetation pass them by, thus becoming decoupled from their best food resources at a critical time of the year. The development of these wells resulted in a 38.65 reduction in green-wave surfing.

These findings can help wildlife managers understand how intact corridors must be in order to retain their ecological functionality, and devise strategies for sustaining mule deer migrations. “The impact is quite clear, but also points to conservation solutions that will allow us to retain viable migrations for generations to come,” explained study co-author Matt Kauffman, a researcher at the USGS Wyoming Cooperative Fish and Wildlife Research Unit at UW. “Once migrations have been mapped, development can be planned in a way that minimizes the disruptions to migrating herds, whether in Wyoming, the American West, or wherever landscapes are rapidly changing.”

“This new research provides the most convincing case, so far, that efforts to minimize development within migration corridors will benefit their long-term persistence amid changing landscapes,” he concluded.

The study is published in the journal Nature.

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By Andrei Ionescu, Earth.com Staff Writer