Alaska's first wild-born and bred wood bison calves were spotted by wildlife biologists Monday, representing a major success for the experimental reintroduction of a species, which has long been extinct in the Last Frontier.

"It was a wonderful sight. What it meant to me is the beginning of those animals being truly wild," said wildlife biologist Tom Seaton, head of the program with the Alaska Department of Fish and Game, which first posted the news on its Facebook page.

Wood bison have been extinct in Alaska for more than a century. Last spring, Fish and Game released a herd raised in captivity into the wild. In the year that followed, some bison died, while calves bred in captivity joined the herd.

Monday's sighting represents the first calves born and bred in the Alaska wilderness.

"That was kind of the moment we've been waiting for," said Seaton, who piloted the plane that spotted the bison calves.

Alaska's herd of about 125 bison is the only wild wood bison population in the United States, according to Fish and Game. Most have stayed within 30 miles of where they were released, near the Southwest village of Shageluk, Seaton said.

The bison's reintroduction has been an experiment, Seaton said.

"All of the animals that went out obviously spent their lives in captivity and there was some doubt whether they could cope," Seaton said. Now, some of those doubts can be put to rest, he said.

Calving season has just begun and will run through mid-June, Seaton said. He expects to see around 30 wild-bred calves this year.

"This week marks the dawn of an era: the era of WILD wood bison conservation in the USA, with Alaska at the helm," the department wrote on its Facebook page.