CASPER, Wyo. — The migratory portion of an elk herd near Cody has hit historically low calf numbers because of drought and increased predation, according to a study released Wednesday.
Drought limits pregnancy, explained Arthur Middleton, one of the authors of the paper “Animal migration amid shifting patterns of phenology and predation: lessons from a Yellowstone elk herd,” published in the journal Ecology. The lower pregnancy levels come at a time when elk also face increased predation from grizzly bears.
The migratory elk will likely not disappear. But their future is uncertain in part because of possible continued drought that some scientists link to climate change.
Grizzly bear numbers have increased in the greater Yellowstone ecosystem. Their diet in some areas is also shifting more toward elk calves than it did before a recent decline in cutthroat trout, Middleton said.
Much of the predation comes from grizzly bears, not from wolves as many would believe, he said. Middleton completed the research while working for the Wyoming Cooperative Fish and Wildlife Research Unit at the University of Wyoming. He is now with the Yale School of Forestry and Environmental Studies.
This study means wildlife managers need to continue limited hunting pressure on migratory animals and liberal hunting opportunities on resident elk, said Wyoming Game and Fish biologist Douglas McWhirter, who also helped with the paper.
Middleton started research on the Clark’s Fork herd when wildlife biologists in the Cody region noticed the migratory elk returning from their summer range with fewer and fewer calves. Migratory elk classically survive better than resident elk because they follow higher quality food.
The opposite seemed to be true in the Cody region. Resident elk from the same herd as the migratory elk found areas with irrigated fields to eat, few predators and more limited hunting on private land, McWhirter said.
“All of those things combined together, what a perfect place for an elk to be and thrive,” he said.
That didn’t explain why the migratory elk continued to have fewer calves.
Researchers discovered after three years of following elk with GPS collars that pregnancy rates were lower in migrating elk. About 90 percent of the resident elk became pregnant each year compared to about 70 percent of the migratory elk.
Migratory cow elk nursing calves were not becoming pregnant. They couldn’t seem to find enough nutrition to finish nursing and produce another calf, Middleton said.
Then once the calves were born, they faced increase predation, especially by grizzly bears, he said.
Bringing calf numbers back up may be more complicated than simply increasing hunting quotas on wolves or black bears, he said.
Habitat projects could help, but options are limited in the wilderness and backcountry areas frequented by migrating elk.
“This highlights how challenging it is to do wildlife management in the Yellowstone ecosystem,” Middleton said. “It’s growing in complexity and hard to manage in that context.”