Leadership
Wolf Leader Pairs Stay Together for Life
Research at Yellowstone Park provides new insights into these predators' lives.
Posted August 25, 2020 Reviewed by Ekua Hagan
This year marks the 25th anniversary of the return of wolves to Yellowstone National Park. The return not only reestablished these apex predators in part of their historic range, but it has also provided a unique opportunity to study the details of wolves’ lives.
Until 1995, wolves had been absent from Yellowstone for close to 70 years, victims of habitat loss and extermination campaigns. In 1973, the Endangered Species Act was passed and wolves were among the first mammals to be listed. After years of planning, the U.S. Fish and Wildlife Service put a reintroduction plan into place. From 1995 to 1997, 41 wolves were captured in southern Canada and released in Yellowstone.
Since then, the wolves have made themselves at home. Kira Cassidy, a researcher with the National Park Service’s Yellowstone Wolf Project, says that since 2009, the wolf population in Yellowstone has been steady around 100.
Since the reintroduction, Yellowstone’s wolves have been monitored using radio collars. The collars allow Cassidy and her colleagues to keep track of all the packs and more easily find them to observe wolf behavior. This includes studies every winter where crew members are tasked with watching a particular pack from sunup to sundown for 30 straight days. Through observational studies like these, the Yellowstone Wolf Project is discovering new information on pack composition and leadership, hunting behavior, and inter-pack conflict.
These discoveries are changing the way we think about wolves. For instance, scientists aren’t so keen on the term “alphas” to describe a pack’s dominant pair anymore. A more appropriate term might be “leaders.”
Wolf leaders don’t gain their position through aggression or conflict, says Cassidy. “What we have found out, not just in Yellowstone but elsewhere, is that wolf packs are families. And those leaders are generally the mother and father of the rest of the pack,” she says.
Family Values
Cassidy and Yellowstone Wolf Project leader Doug Smith recently presented new findings on pair bonds between pack leaders at the Animal Behavior Society 2020 Virtual Conference. Using observations from the time of reintroduction through 2019, they identified 152 distinct dominant pairs.
The majority of these pairs only terminated when one or both leaders died (~76%) or when one leader switched to a subordinate role in the pack (~14%), which can sometimes happen in the case of an injury.
Their divorce rate was exceptionally low. “Of all the pairs that formed over 25 years, only 9% ended up separated from each other,” says Cassidy.
Female wolves usually make out better than males following divorces. Wolf society is matrilineal, with the territory passed down from mother to daughter or sister to sister. After a divorce, wolf females tend to stay with their pack and territory and re-pair with another male, while males leave and try to find a new territory.
Cassidy says that it's tough to say why pairs divorce, since they only saw ten instances of it. Four of those times, the divorced female accepted a group of males into her pack and bonded with the most dominant one. Having extra males around could help a pack out in a few different ways. More males (which tend to be bigger than females) could mean the ability to take down larger prey, like bison or a bull elk. Also, in the fights that happen when packs run into each other, having more adult males is an advantage.
Experience and Wisdom
These territorial fights are a major part of wolf life; in fact, they are the number one cause of wolf mortality.
In another recent study, Cassidy and colleagues analyzed the outcomes of wolf pack fights. They thought it would simply be a matter of numbers, with the larger pack winning. That’s the pattern found in other species, such as chimpanzees and lions.
But when the researchers looked for a factor that could help a smaller pack win even if they were outnumbered, they were surprised to find the most important variable was just having an old wolf present.
Old wolves are likely pack leaders, and although they are not as physically strong anymore, they still make a lot of decisions for the pack. But they don’t participate as much in fights.
Cassidy says they see this in hunts, too. “The older wolves let the younger, faster, stronger wolves in the pack make the kill and then they will come in to eat at the end,” she says. “We found that even though they don’t do a lot of the fighting, their presence makes a huge difference in these fights.
“If you live in a big pack and everyone is taking care of each other and valuing these elderly wolves, then you’ll do much better when fighting with other packs, reduce your mortality, and increase everyone’s survival.”
Lupine Lessons
For Cassidy, it is a special experience to be able to see so much of an elusive animal and follow their individual stories. One of the packs she studies, for instance, has been in existence since the reintroduction.
“I think there were six of them brought down from Canada and released in 1995,” she says. “And now, seven generations later, wolves from that same lineage are still there.”
While analyzing data for the wolf pairs project, Cassidy noticed some unique behavior in this pack. On two separate occasions in their history, the lead male died during hunting and his partner waited a long time — over a year — before finding a new mate.
Cassidy says a wait this long is extremely rare. “For the most part, 75% of the time, they have a new mate within two weeks,” she says. “Most of the time, it’s within a few days, even. For a pack to operate so long without a lead male, seemingly with no problems, is unusual.”
One of those females even had pups. The researchers don’t know who she ended up breeding with but “it was clearly a temporary arrangement,” according to Cassidy. This female had pups in the spring but did not allow a male to join as her mate until summer when a new male arrived. He hung out with her pups at a rendezvous point before fully meeting other members of the pack and being allowed to stay.
Cassidy says that we humans can learn some things from wolf behavior. “I am constantly impressed by their resilience in the face of hardship,” she says. “And I think what we’re finding out about pair behavior adds another layer to that. Wolves have to cooperate to catch every meal. And they are doing this with another wolf that they clearly care about and want to stay with.”
Another pack that Cassidy has fond feelings for is one that formed about the same time she started her job with the National Park Service, in 2007. At that time, there were two wolves just under two years old forming a new pack. One of Cassidy’s first assignments was to go watch them.
“They ended up staying together for almost nine years, until the male disappeared and then the female died,” says Cassidy. “In Yellowstone, wolves live for an average of three to four years. These two were both exceptionally old, almost eleven years — ancient in the wolf world.
“We’ve only had a handful that live to be over ten, so for both of them to live to be that old and stay together that whole time is really unique. I watched them for so many years and thought they were the best example of a good relationship I had ever seen.”
References
Cassidy, K.A. and Smith, D. W. Do gray wolves mate for life? Patterns in pair bonds from Canis lupus in Yellowstone National Park, WY. Animal Behavior Society 2020 Virtual Conference (July 28-31, 2020).
