Every spring, tens of thousands of elk follow a wave of green growth up onto the high plateaus in and around Yellowstone and Grand Teton national parks, where they spend the summer calving and fattening on fresh grass. And every fall, the massive herds migrate back down into the surrounding valleys and plains, where lower elevations provide respite from harsh winters. These migratory elk rely primarily on environmental cues, including a retreating snowline and the greening grasses of spring, to decide when to make these yearly journeys, shows a new study led by University of California (UC), Berkeley, researchers. The study combined GPS tracking data from more than 400 animals in nine major Yellowstone elk populations with satellite imagery to create a comprehensive model of what drives these animals to move. "We found that the immediate environment is a very effective predictor of when migration occurs," said Gregory Rickbeil, PhD, who conducted the analysis as a postdoctoral researcher in Dr. Arthur Middleton's lab at UC Berkeley. This is in contrast with some other species, such as migratory birds, which rely on changing day length to decide when to move, Dr. Rickbeil pointed out. The results, published in the July 2019 issue of Global Change Biology, suggest that, as climate change reshapes the weather and environment of the park, elk should have the means to adjust their migratory patterns to match the new conditions.
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