Alaska Fish & Wildlife News
October 2024
Re-Wilding Wood Bison
Soft release, anchoring, and lessons learned
Giant wood bison roamed the expansive sedge meadows of Alaska for thousands of years before disappearing early in the 20th century. Now, close to 150 wood bison in two herds are foraging in the meadows and mixed forest of Interior and Southwest Alaska.
This summer, 58 wood bison, originally from Canada, were transported to the Minto Flats State Game Refuge west of Fairbanks. This wetland meadow complex of almost half a million acres lies in just about the geographic center of the state. These bison are getting a “soft release” that will help anchor them to their new home on the range.
About 400 miles southwest, another group of wood bison roams the Lower Yukon River region near its confluence with the Innoko River. They were released there in 2015, the first wood bison to be restored to the wild anywhere in the United States. Over the past nine years the population has had its ups and downs and is adapting to the landscape. Biologists applied lessons learned from these animals to the transfer and re-wilding of the 58 new bison.
All these wood bison are originally from Canada’s Elk Island National Park, which is a carefully managed source population used to reintroduce wood bison throughout their original range in Canada, and now Alaska.
Wood bison are closely related to plains bison, but are spectacularly well-adapted to northern life (see the companion article). The original range of wood bison extended across central and northwestern Canada and into Interior and Southcentral Alaska. They were near extinction by the early 1900s, with a few isolated populations remaining in northern Alberta and the Northwest Territories.
Restoring bison
Tom Seaton has been involved with wood bison for 15 years and serves as the Wood Bison Restoration Project biologist for Fish and Game. When restoring wood bison to the wild, there are several key considerations. As might be expected, habitat with good forage is primary.
“Does the area have the forage to support bison?” he said. “Are there enough grasslands to allow for growth in the population over the next century? Is there enough room for 500 or more bison? That is the minimum number of individuals needed to ensure genetic mixing and to keep the population genetically diverse over time.”
Bison have been on the Lower Yukon for almost a decade and Seaton, who is also a pilot, has flown there many times from his base in Fairbanks to monitor the animals. Every year in June, a team flies an aerial survey using a camera-equipped aircraft to assess the population. About a dozen animals are collared, which enables biologists to locate groups of bison. They’ve found that during hard winters, mortality had been high. During easier years Seaton has been impressed by the growth of the population, sometimes near 20 percent. When he and his colleagues flew down in June this year, they found it was a banner year for calves.
“We saw 21 calves, which is a lot for a population of 70-some animals,” Seaton said. The difficult winters may have winnowed the population down to the hardiest bison. “Our minimum count in June of 2024 was 74 bison.”
Based on the distribution of animals and the forest cover in some areas, the survey team suspects that there are more animals. A survey planned for early winter may confirm that.
Weathering winter
Snow is a key factor affecting bison survival over winter. Forage in the Lower Yukon-Innoko area is high quality and abundant, but when snow conditions inhibit access to that forage, winters can be challenging. Over the past decade, three unusual winters were especially difficult for wood bison. He's learned that snow conditions, especially in late winter, are critically important for bison.
He said a bison has to sweep the snow away with its face to reach the forage, and a bison can do that through 40 inches of snow if it is soft. Layers of crust and ice can be a problem.
Another key questions is, when does the snow melt? “Some years it melts as early as March. Some years it lasts until late May.”
Moose, bison, caribou, sheep and deer survive winter by gaining weight all summer and storing up body reserves in muscle and fat. That only takes them so far.
“They are getting some forage in the winter, and that affects the rate of weight loss, but in winter it’s not enough. They run out of reserves. They need to make it to green up before those reserves are exhausted in order to survive. We can lose 30 percent, 40 percent, or more of a population of moose, caribou, deer, sheep, or bison in an area in a winter.”
In the decade prior to the bison release in the Innoko, there were several low-snow years and people complained of not having enough snow to adequately run snowmachines. But weather data in western Alaska shows that since 2015, snow has been unusually deep and persisted into spring, compared to the last 100 years.
“It’s been the harshest late winter conditions in a century,” Seaton said. Losses those years include an estimated 30 to 40 percent of the moose in the area south of Fairbanks, GMUs 20A and 20D, losses of plains bison in the Delta Junction herd, and losses of as much as three-quarters of the Dall sheep in some areas. “Let’s hope that in the future we get back to more of a normal winter weather pattern.”
Historical patterns may be a poor predictor of future conditions these days, but difficult snow conditions have been less frequent in Minto Flats, occurring about once every 30 years, Seaton said. “There was a difficult one in the late ‘60s, in the early ‘90s, and an extreme ice storm in 2021.”
Minto Flats: the soft release pen and anchoring
Early this summer, a crew spent almost six weeks along the Tanana River, near the mouth of the Kantishna, preparing the release site. About a dozen staff and volunteers built a soft release pen, a 100-acre enclosure that will be home to the wood bison this fall and winter as they adjust to life in the wild. That gradual acclimation is known as a soft release.
“Soft release is far more likely to result in a successful establishment of wild populations, from carnivores to ungulates,” said Wildlife Biologist Darren Bruning. “It’s a proven and highly effective technique.”
Bruning has close to forty years of experience managing wildlife. He worked with plains bison in Delta Junction and all of Alaska’s wood bison. He’s had considerable experience caring for animals and preparing them for transport, moving them, and releasing them into the wild - projects ranging from bison to otters to bighorn sheep.
“Animals are stressed when they are captured, however you do it,” he said. “Then they get poked and prodded, and then taken to a place they don’t know. It’s disorienting. You don’t just open the gate and say go!”
Two-and-a-half miles of fencing enclose 100 acres of prime habitat. The eight-foot-high wire game fence was fastened to trees, not posts, using tie wire and not fence staples. Brush and logs were used to fill in low spots. There are no corners, just smooth curves. It follows the land and the ridges that roughly encompasses a wet sedge meadow and some upland mixed forest.
“It works really well and when we’re done, there are no staples to pull and no damage to the trees,” Tom Seaton said. “Having such a nice big pen, the bison will get used to the forage, which is really helpful with this re-wilding.”
It is big. For comparison, a football field including the end zones is 1.32 acres. So, this area could hold 66 football fields.
“It’s good habitat,” Bruning said. “All the area, a mile out, five miles out, all has high quality forage like this.”
Seaton said it’s pretty wet in the middle of the pen, but in the winter, that’s where they’ll spend a lot of their time. “These wet meadows become dry prairie in mid-winter, and the sedge becomes 90 percent of the diet.”
In addition to the pen, the crew built a half mile long “alleyway” from the off-loading site on the riverbank to the pen.
“The pen and alleyway - it’s the eighth wonder of the world,” Bruning said. “A lot of bushcraft and incredibly hard work went into building it, it’s really sturdy. If bison don’t have a great reason to feel they have to leave the area, they won’t challenge the fence.
Moving bison
Bruning has been involved with every wood bison release in Alaska. “At this point we’ve moved more than 200 bison without mortality, or major injury or issues,” he said.
Bison are transported in large, customized shipping containers. In July, 41 bison were trucked from the Large Animal Research Station in Fairbanks to Nenana, and in late August, 17 bison were trucked from the Alaska Wildlife Conservation Center near Girdwood to the same location – Ruby Marine in Nenana on the Tanana River. From there, bison got a seven to nine hour barge ride down the Tanana River to the Minto Flats State Game Refuge site, near the mouth of the Kantishna River.
Bruning said planning, preparation and knowing how to act around bison reduces the stress as much as possible. A veterinarian accompanies the biologists and barge crew.
“Their demeaner while we are transporting them is very calm,” he said. “We minimize the time we are in their presence. We don’t talk around them and there are no sudden, unexpected loud noises. There’s plenty of food so they’re not grumpy. The barge crew has been amazingly great. They want to know how to act around the bison, and they are to be commended how they’ve embraced minimizing stress for the bison.”
“The river is cool, air is moving. Once we are at the site, it takes a good solid two-and-a-half to three hours to get everything ready to offload them. Then we open the containers to let bison walk off the barge, it probably takes an hour and a half to offload. They walk to the soft release pen at night. Nighttime provides an extra calming factor. The darkness is comforting to them.”
When they arrive at the meadow, they have time to orient and breathe. “They are smelling the air, the grass, recognizing those smells, recognizing there’s water and food,” Bruning said. “Their stress levels diminish. They are alive and well and stabilizing. They see they are with their own kind; they re-form their social structure, they eat and drink, getting used to the landscape.”
The bison will spend the winter in the pen and be released to the wild in late spring. Those nine months in the pen will help anchor the bison to the area.
At least two people will spend the winter at the site, as well as visitors, including Luke Rogers, Bruning and Seaton. They’ll provide some supplemental food and monitor the herd and the fence. They will have snow machines and will walk or ski the perimeter every day. Wall tents and a couple WeatherPorts will provide shelter, and they’ll melt snow for drinking water.
Anchoring bison
“We’re holding them for a pretty long time, “ Bruning said. “That helps anchor bison to the site. It becomes their home.”
In the spring, it’s likely that cows will calve in the soft release pen. Seaton said cows almost always include the calving site in their home range. That makes it part of their seasonal range.
“We’ll release them when there’s a flood of good forage on the landscape, right at green up,” he said. “It’s an easier time for them, they don’t have to walk long distances, they’ll gain weight fast and not be searching for food. At green up, the calves are quite small and not able to travel very far, and the cows know that. Those cows with calves are the leaders in this matriarchal society, and the slow pace of the calves minimizes the speed of the entire group. A particular group of cows will stay together for most of their life. The calves stay until they are about three, then males go off and do their own thing.”
Three years is a relatively long time for an animal to care for its young. That social structure is one reason why bison are so adaptable to many different habitats. “They learn,” Seaton said. “They figure out how to prosper in different places, and pass that on to their young.”
More on bison and Minto Flats
Minto Flats State Game Refugehttps://www.adfg.alaska.gov/index.cfm?adfg=mintoflats.main
Wood bison restoration in Alaska – webpages include history, herd status and updates, FAQs and additional links
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