Wolf packs are less likely to stick together after human impacts

A study led by the Yellowstone Wolf Project is shedding new light on how humans are impacting wolf populations in national parks. The researchers found that human-caused mortality triggers instability among wolf packs. In particular, the team found that human activities such as trapping and legal hunting have detrimental effects on reproduction and pack persistence among gray wolf populations. 

“Gray wolf management is rarely simple and transboundary wildlife issues are complicated by disparate management goals,” wrote the researchers. “Despite our study focusing on gray wolves that primarily lived within national parks and preserves, we documented high levels of human-caused mortality, most of which occurred outside protected-area boundaries. Of greater concern, these mortalities had detrimental effects on gray wolf pack-level biological processes.” 

The team analyzed decades of data for gray wolf packs living primarily within Denali National Park and Preserve, Grand Teton National Park, Voyageurs National Park, Yellowstone National Park, and Yukon-Charley Rivers National Preserve. To conduct the study, Yellowstone research associate Kira Cassidy collaborated with experts from all five national parks and from the University of Minnesota Voyageurs Wolf Project. 

“For gray wolves, the biological unit is the pack or the family. We wanted to focus on the impacts of human-caused mortality to the pack, a finer-scale measure than population size or growth rate,” said Cassidy. “We found the odds a pack persists and reproduces drops with more human-caused mortalities.” 

To investigate, the researchers examined wolf packs after at least one member was killed by human causes and compared these groups with packs that had not experienced human-caused mortality 

The study revealed that the likelihood of a pack staying together until the end of the year decreased by 27 percent after human-caused mortality, while the rate of reproduction dropped by 22 percent. The impacts were even more severe when a pack leader died, with the odds of pack persistence dropping by 73 percent and reproduction declining by 49 percent.

Wolves in Voyageurs National Park spent the most time outside of park boundaries. As a result, 50 percent of all deaths among this population were attributable to humans, and poaching was the predominant cause.

“The unique shape of Voyageurs means that there are very few wolf packs that live entirely within the boundaries of the park. Instead, many wolf pack territories straddle the park border and when wolves leave the park, they are at an increased risk of being killed by people,” said study co-author Thomas Gable.

“Rather than viewing this result as a failing, we hope this work encourages a renewed interest in interagency collaboration, where management of gray wolves is defined by compromise and based on science, including weighted space-use and cause-specific mortality data,^ concluded the study authors. “If efforts are made toward this goal, these protected areas and the partners involved can serve as a model for successful transboundary issues worldwide.”

The study is published in the journal Frontiers in Ecology and the Environment.

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By Chrissy Sexton, Earth.com Editor

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