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Wolf killing and the consequences of disturbing pack dynamics

By
Christine Peterson with WyoFile, via the Wyoming News Exchange

The last few years have been tough for gray wolves. Idaho passed a law to kill up to 90% of the state’s wolves. Montana killed 270 in one season. Wisconsin killed about 220 before the species went back on the Endangered Species List. Some 25 wolves killed in the Yellowstone National Park area in 2022 came from the park itself. 
 
Proponents of the cull say too many wolves are on the landscape, and even removing large portions of packs won’t make much impact on overall populations. Short of the mass annihilation of a century ago, they’ll bounce back. They’ll be fine. 
 
But a large study published earlier this year looking at wolves within five national parks across Canada and the U.S. shows that while wolf populations may recover quickly, their social structures don’t. 
 
And, the authors argue, the way wolves function on a landscape — how breeding pairs order their packs, how and when they choose to reproduce, for example — is an important part of our natural systems. So the mortality of a single animal could have significant implications. 
 
“You kill the wrong wolf at the wrong time, that pack could blink out or won’t reproduce,” said Doug Smith, recently retired wolf biologist with Yellowstone National Park who co-authored the paper. “Their social dynamics are fragile. We made no value judgment on killing wolves. We’re just saying this is 100% what happens if you do.”
 
In Wyoming outside of the national parks, where wolves have been managed by the state for the better part of a decade, biologists say they’ve found a way to allow wolf hunting, keep livestock depredations in check and preserve stable pack structures. It’s possible with enough data and attention to wolf management, said Ken Mills, Wyoming Game and Fish’s wolf biologist. 
 
Understanding what happens when wolves die requires first knowing how wolf packs function. 
 
“Because wolves are social and populations are built on packs, you won’t have a collection of individual wolves. That’s elk and deer,” Smith said. “Wolf packs don’t exist as individuals, they exist as groups in packs.”
 
Each pack has, in general, three age classes: The breeding pair and their offspring, which are non-breeding adults and pups. Depending on the size of a pack, there could be three to five non-breeding adults. If one of the breeding wolves dies, another one of the adults could step up to breed unless they’re related, in which case a wolf from outside moves in, Smith said. 
 
Some packs will be as small as four or five individuals, others like Yellowstone’s Junction Butte Pack can be as large as 20 — though Smith said that’s uncommon. The average Yellowstone pack size hovers around 10 individuals.
 
Packs then claim certain territories, and they don’t take those claims lightly.
 
The biggest killer of wolves is wolves, largely in territorial disputes, said Kira Cassidy, lead author on the new paper and research associate with Yellowstone Wolf Project. Most packs tend to stick to their ranges unless another pack dissolves or becomes particularly vulnerable, usually due to the loss of adults. 
 
Packs naturally break up and re-form even without human-caused mortalities from hunting, car collisions, trapping or poaching. About eight to 10 packs typically occupy Yellowstone, though on average, Cassidy said one dissolves and another forms each year. 
 
When a pack does dissolve, remaining members typically strike out on their own initially. 
 
“There’s usually only a handful [of individuals] left,” Cassidy said. “They become dispersers or lone wolves by default.”
 

 
Rarely they may join an established pack — Yellowstone biologists have only recorded an unrelated adult joining an established pack as a subordinate a couple dozen times in the last 28 years. If they’re lucky, these lone animals pair up and find a niche territory they can claim as their own. But more often than not, they’re dead within a year. 
 
Dispersing wolves are more likely to run into humans while seeking food, or they die trying to scavenge another pack’s kill.  
 
“They’re exposed to a lot of mortality out there, much more than just the short time the hunting quota is open,” Cassidy said.
 
In the winter of 2021, politics in Montana changed. Lawmakers decided to lift wolf quotas around Yellowstone, opening the area bordering the park to a free-for-all. In Idaho, meanwhile, lawmakers passed a bill allowing year-round wolf trapping on private property, unlimited purchase of wolf tags and any method of take for any wild canines. Wolf killing began in earnest. 
 
Wolves from packs in Yellowstone strayed from the park into Montana and were shot. 
 
As Cassidy watched this unprecedented killing of park wolves, she said, she began to realize this was a chance to determine how packs respond not only to losing individuals, but if it mattered which individuals were killed.
 
Not long after the park wolves were killed, Cassidy — who came to Yellowstone National Park 16 years ago to study wolves, predominantly their social structures —  started noticing differences. Packs like the Junction Butte Pack lost about a quarter of its members, but most were pups and yearlings and the pack stayed intact. Smaller packs like Phantom Lake Pack simply dissolved. But the role of the pack member  killed also had a bearing. When the oldest members, one or both of the breeding pair, died, the pack was much more likely to disintegrate.
 
What she found in Yellowstone was not unique to the system. Combined with parks and protected areas across North America, it showed a pattern. A pack was 27% less likely to survive if any member died of human causes, her report concludes. If a pack leader died, the pack was 73% less likely to make it to the end of the year intact. 
 
Just like in a human family unit, Cassidy said, lose a leader and the void can be tough to fill. 
 
What all of this means depends on who you ask. For retired biologist Smith, it means a greater understanding of how a natural system functions, which provides managers the data they need to make informed decisions about wildlife. 
 
For Mills, the Wyoming biologist, it reinforces what he already knew. Higher wolf density outside of Yellowstone has a clear correlation to higher livestock depredations. But keeping numbers steadily around 160 with at least 10 breeding pairs has shown over the last decade to keep livestock depredations to a relative minimum. 
 
In 2016, the U.S. Fish and Wildlife Service killed about 90 wolves for preying on livestock in Wyoming’s trophy game area when numbers were high — due in part to the fact that wolves were on the Endangered Species List. Since then, the number of wolves killed by agency officials because of conflict plummeted: 15 in 2022 and 14 in 2021. Total 2022 mortality in the trophy game area, including hunting, lethal removal and natural mortality, was 53. Even with hunting, packs in Wyoming tend to stay together for an average of six to seven years, Mills said. One pack, the Beartooth Pack, has survived relatively unbroken since 2000.
 
“The evidence suggests if we manage wolves at high densities, like they were when they were relisted in 2014, then wolf population exceeds carrying capacity,” Mills said. Then, instead of wolves curbing reproduction or dying off from lack of wild food, they started eating livestock.
 
Mills agrees that hunting can impact pack social structures. It’s why Wyoming structured its hunting seasons in a way that provides opportunity but avoids times when breeding individuals are most vulnerable, he said. Years of data have now shown that keeping most packs intact and wolf numbers below what the landscape will support will maintain wolf packs and help minimize conflict. 
 
Packs can have their own cultures engrained in individual members, Cassidy said, and some packs are more interested in eating livestock than they are elk, deer or other wild prey. If agencies use a scalpel approach, they can eliminate that pack and its replacement may be more inclined to focus on elk and less on cattle. 
 
Mills has also realized that maintaining packs that stay out of trouble keeps Wyoming above the 10 breeding pairs threshold. Consistently kill wolves too close to breeding season or in breeding season and packs may dissolve or fail to reproduce that year. 
 
It’s a balance, Mills notes, but one he feels Wyoming has been able to maintain over the years. 
 
Now, more than a year later, Yellowstone’s overall wolf population has remained largely unchanged around 108 wolves. Packs also increased. Yellowstone lost two packs after the 25 park wolves were killed, and gained four with no signs of those dissipating. And after the 2021-2022 season, Montana reinstated a hunting limit of six around the park.
 
For Cassidy, pack lineages should be valued by humans as important biological processes just like big game migration routes. 
 
“No one wants a wolf population that is 80% pups, and the best way to get away from that is to help preserve some of the pack lineages,” she said. “Acknowledging our impact is important in understanding how we’re operating in the world and how animals are operating around and beside us, even just that understanding works to a better coexistence.”
 
WyoFile is an independent nonprofit news organization focused on Wyoming people, places and policy. 
 

 

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