How people break wolf packs

This article originally appeared on High Country News.

Packs are to wolves what families are to humans: They are the species’ most essential social structure. The dynamics of a wolf pack—who the leaders are, how the members raise cubs, how they hunt their prey, and how they respond to threats—determine the survival of the group.

But until now, most wolf research has focused on the population of the species as a whole, rather than individual packs. Wolf populations tend to remain fairly stable despite human-caused mortality. But we also know that some wolves avoid busy roads, that heavily hunted wolves have high stress hormones, and that human development disrupts wolf habitat. This gap in understanding led a group of National Park Service employees and biologists to ask the following questions: How does human activity change individual wolves? packs?

That question prompted a new study, recently published in the journal Frontiers in Ecology and the Environment. The research analyzed how human-caused deaths – from hunting and poaching to car accidents and research captures – affected nearly 193 wolf packs in five national parks and preserves. The researchers used data collected in those fields between the late 1980s and the present day. A little more than a third of the collared wolves living primarily in those protected national parks died of human causes, and those deaths had negative consequences for some of the packs.

Packs affected by human-caused wolf deaths were less likely to reproduce, and losing a pack leader reduced the chance of the pack staying together or having cubs the following year. The researchers also found that pack size mattered: Packs that were smaller were more likely to disintegrate first, while larger packs were more resilient. “If human families have to deal with the death of family members — like two in a row, or the head of the family — that would be much more upsetting and difficult to get through,” said lead author Kira Cassidy, associate research with the National Park Service’s Yellow Wolf Project. Larger packs have more members waiting in the wings to take on any responsibilities and duties that may be left unfilled due to a sudden void in the pack.

Packs affected by human-caused wolf deaths were less likely to reproduce, and the loss of a pack leader reduced the chance of the pack staying together or having cubs the following year.

Cassidy said she recently saw this in Yellowstone. As of late 2021, before hunting season, the park’s Junction Butte Pack had 28 members, making it a fairly large group. Eight wolves, all young, were legally killed by hunters outside the park. The group came back quickly; In the spring of 2022, there were four litters of calves in the pack, and there are now 25 members. A smaller pack may have broken up and scattered, or not reproduced in that size. “Socially, they’re vulnerable,” said co-author Doug Smith, a recently retired Yellowstone senior wolf biologist.

The study shows the importance of tracking wolf packs, rather than just population numbers, said Mark Hebblewhite, a professor at the University of Montana who is not involved in the research studying wolves and ungulates. This new understanding shows wildlife managers that human boundaries cannot always protect wildlife. “This paper recognizes that national park animals such as wolves and bison are at risk of being removed when they leave the park,” Hebblewhite said. “They spent the whole summer looking at hundreds of cars and thousands of people, and those people don’t do anything bad to them. And then they leave the field, they walk right in front of a dressing camp, and somebody shoots them with a hammer.”

The authors hope that the study will encourage more cooperation between national parks and neighboring states to limit the human effect on wolves living near the edges of protected areas. “This paper could be useful not only to show how important packs are, (but also) how important it is for us to understand how we are responsible for influencing other species,” a Cassidy said. “I’m quite proud that this study gives people the information to say, ‘This is our impact.'”

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