Dozens of Alaska wood bison succumbed to hard weather and hungry wolves last winter, causing an experimental herd population to drop below where it was when the herd was introduced to the western Interior in 2015.
Wood bison are a larger subspecies of the plains bison found in the Lower 48. They have larger, blockier humps and shorter, pointier beards. They’re the largest native land mammals found in North America. Before 2015, wood bison were extinct in Alaska but oral histories and bone records indicate that large herds lived here hundreds of years ago, and a few survived into the early 20th century.
Alaska’s current population of wood bison was imported from Canada and released near the village of Shageluk in the Innoko River basin of Western Alaska. For more than 20 years, the Alaska Department of Fish and Game had been planning to reintroduce wood bison to Alaska to enhance grazing ecosystems, provide another large animal for people to hunt, and help the international effort to restore the sub-species from the near extinction it reached in the 1950s.
The Alaska herd numbered 130 bison when an airplane and a barge transported the animals to their new range in 2015. After this winter’s die-off and low birth-rate of new calves, the herd now numbers 91 bison, according to a population survey done by the state Fish and Game department in June. It’s “possible, but unlikely” that additional bison weren’t counted in the population survey, said wood bison project leader Tom Seaton, a Fairbanks-based biologist with the Alaska Department of Fish and Game.
Hunting goal delayed
There had initially been hopes in Alaska that the herd would grow fast enough to allow some hunting within about six years. That estimate now looks overly optimistic.
“From the first three years of evidence, it’s going to be longer than that. It’s going to be longer than a decade. It’s going to depend on what the weather’s like,” Seaton said.
The herd’s management plan calls for allowing a small bison hunt when the herd reaches a population of about 250 animals.
Seaton said this past winter was especially hard on the wood bison because of frequent snow and rain that fell in the Innoko River basin from late February to late April. Wood bison use their faces to wipe away snow and reach grass and sedges to eat below. As the snow gets deeper or develops more hard layers, the bison have to expend more energy to eat.
Biologists knew that deep snow was a risk in the Innoko River, but the area was chosen to avoid conflicts with future oil and gas developments in other areas that were being considered for the bison release such as Minto Flats and Yukon Flats, Seaton said.
Other large animals in the western Interior had their lowest calving rates in 20 years this spring, indicating this winter was extraordinarily difficult.
These animals include moose populations around the wood bison herd and plains bison from the Farewell Herd. The Farewell Herd bison are descendants of plains bison imported from Montana in 1928. The Farewell Herd bison live east of the new wood bison herd.
Since their release, the wood bison have wandered in different directions, traveling as far north as the Brooks Range and as far southwest as the Yukon-Kuskokwim Delta. But the herd has generally kept within a 75-mile north-to-south range bordered by the village of Holy Cross to the south and the ghost town of Holikachuk to the north and to within a 20-mile east-to-west range.
Wolves get a
taste for bison
Biologists believe wolves played a significant role in the wood bison decline this spring in concert with the deep snow and slow thaw. It’s unusual for wolves to pose a serious threat to wood bison. Adult male wood bison weigh more than 2,000 pounds, a good 25 percent bigger than the largest moose. Female wood bison are smaller, but still massive, growing to about 1,200 pounds. But this winter’s conditions made it easier for wolves to hunt the massive animals.
“Wolves had a major advantage during these two months (March and April) because they could run on top of the snow and bison (and moose) had a very difficult time moving. As the weeks went by, the wolves got stronger from eating so well and the herbivores got weaker from the increased harassment by wolves and the lack of access to forage,” Seaton wrote. “It is estimated that about one-quarter of the bison deaths in spring 2018 were directly from wolf predation; harassment by wolves most likely contributed to loss of body reserves and subsequent death of others.”
When the wood bison were first released, drowning was a major cause of death. At least nine bison stepped onto rotting ice and drowned during the first spring in 2015. The death rate dropped as bison got used to their range over the next two years and the birth rate climbed.
Plans for more wood bison
Wood bison have continued to multiply in Canada and surplus bison there are available for re-introduction in Alaska.
This fall, the Alaska Department of Fish and Game plans to start planning for future wood bison releases in Alaska, Seaton said.
• • •
Contact Alaska News Miner staff writer Sam Friedman at firstname.lastname@example.org or follow him on Twitter: @FDNMoutdoors.