A group of 100 wood bison has been sent into the open wild near Shageluk. It’s the final step in a reintegration process that has been in the works for nearly 20 years.

Last month the bison were transported by plane from the Alaska Wildlife Conservation Center in Portage to the small western Alaska city. They’ve been held in temporary pens ever since.

Alaska Department of Fish and Game biologist Tom Seaton opened the gates to the pens early Friday. The bison followed his snowmachine across the Innoko River to grass meadows in the Lower Innoko/Yukon Rivers. The Division of Wildlife Conservation spokesperson Cathie Harms said they had already started behaving like wild animals.

Each of the bisons was outfitted with a radio collar in order to study their roaming patterns and how their new habitat is affecting them.

This is the first population of wild wood bison in the United States in more than a century, according to the AWCC. The animals were native to the Alaska, but were driven to extinction by over-hunting. The AWCC received about a dozen wood bison from Canada in 2003.