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Wood Bison Transition to Wild Population

Thirty nine days after leaving their captive home at the Alaska Wildlife Conservation Center in Portage, AK, project leaders say wood bison are becoming wild animals and are on course to form a strong, successful herd.

The animals were released into the Lower Innoko/Yukon Rivers area on April 3 to restore the species to historic range in Alaska. Biologists are monitoring the movements and numbers of bison throughout this summer.

Department staff confirmed that at least six calves have been born so far, and more are expected soon. Calving season for the species runs from late April through mid-June.

According to Wood Bison Project leader Tom Seaton, the animals converted immediately to a wild diet of sedges and grasses. The animals have been seen in many places where forage is abundant.

“They separated into group sizes common for wild bison and have spent the last few weeks exploring new habitat. Some of the bison traveled up to 16 miles northeast of the release site, while others stayed within a few miles,” Seaton said.

Most of the animals quickly became wary of people. Biologists on foot and on snowmobile encountered bison within the first week and the bison reacted by being alert, then moving away, as wild animals do. One 11-month old calf returned to the soft release pen area for about two weeks, but then rejoined the herd.

“The wood bison are showing behaviors of a wild population, including feeding, bedding and avoiding humans. The herd is doing well,” Seaton said, adding, “This is an experimental population. They’re not inside a fence anymore, their fate is up to them and nature. We continue to have very high hopes.”

Based on results of other herds established in Canada, biologists knew that some bison would be lost during the transition from captivity to the wild. Over the past two weeks, nine bison ventured onto degrading ice, fell through and drowned. Another five died during the last 39 days and staff are still investigating causes. So far, no bison have died as a result of predation.

Seaton says this level of losses in the new herd were fully expected and normal. “Bad ice is a problem for many wildlife species, and we knew it would be a factor in the Lower Innoko area. Bison released from captivity need time to learn about natural hazards,” Seaton said. “Natural selection is a difficult and challenging process for wild animals, but it ensures that only the strongest and best adapted animals survive to establish the next generation. Through the process, the herd will get stronger and stronger as the years go by.”

Seaton said the losses do not compromise the herd’s chances for success. ADF&G needed to release a minimum of 30 animals to establish the Lower Innoko/Yukon Rivers herd, but with generous support and donations from partner nonprofits and businesses, Alaska was able to transport and release 100 wood bison. Starting with such a large number of bison to the Innoko allowed for losses without endangering the future success of the herd.

Re-introduced populations of wildlife in North America have been known to lose as many as half of the animals before stabilizing. Drowning is a leading cause of the death in wild wood bison populations in Canada, and is also a significant cause of death for moose in Alaska.

Meanwhile, plans are underway to transport 28 adult bulls from the Alaska Wildlife Conservation Center in Portage to the Lower Innoko area. The bulls are significantly larger than the adult cows transported last month, some tipping the scales at more than a ton. They will be trucked to Nenana, loaded onto a barge for a week-long trip down the Tanana and Yukon Rivers before traveling up the Innoko to the release site. The large bulls are scheduled to be released in late May and early June, before the breeding season in late July and early August.