BILLINGS — A privately funded conservation reserve taking shape on north-central Montana’s open prairie now spans more than 300,000 acres — or almost 470 square miles — with the addition of a large parcel south of Malta that was disclosed Thursday.

American Prairie Reserve manager James Barnett said the group recently bought a 22,000-acre ranch in Phillips County that will be known as Sun Prairie North.

The Bozeman-based group described the purchase as an important step in its goal to piece together more than 3 million acres of public and private lands. That’s an area larger than Connecticut.

The end-game is the free-flow of wildlife — including up to 10,000 bison — across an area along the upper Missouri River roughly 60 miles south of the Canada border. 

Several of the scattered large plots controlled by the reserve connect with the Charles M. Russell National Wildlife Refuge. 

Some surrounding ranchers say the project is slowly eroding their remote agricultural communities and threatening their way of life. Despite such objections, owners of 14 ranches have voluntarily sold out to the reserve since 2004.

Among the project’s financial supporters are John and Adrienne Mars. The candy-industry billionaires have given more than $20 million to the American Prairie Reserve. Total donations to the project as of last year were $67.3 million.

The reserve currently has about 400 bison, a figure that has been steadily increasing with new births and animals imported from Elk Island National Park in Alberta.

A biological assessment of Sun Prairie North over the next several months will determine if that site also would be suitable for bison, Barnett said. Tens of millions of the animals once roamed the plains of North America before over-hunting nearly drove them to extinction.

“The importance of the property is it’s very centrally located between many of our holdings, which in the long term reduces habitat fragmentation,” Barnett said. “The property is also important for sage grouse, and has good habitat for other wildlife out there like pronghorn, elk and deer.”

Phillips County rancher Leo Barthelmess said the purchase came as no surprise to the area’s closely knit agriculture community but was nevertheless disappointing.

“I’m always disappointed when another neighbor or community leader chooses to sell to the American Prairie Reserve and leave the community,” he said.  

As the reserve has grown, it has come closer and closer to Barthelmess’ property, roughly 20 miles to the north. But he said he would not sell if approached by the group and intends to remain on the land “for years and years and years.”

Public access to parts of the reserve is allowed, and not all of its lands are under conservation easements. 

Some of the parcels acquired have been leased back to their original owners, so the properties still could be used for cattle grazing. That includes a 12-year-lease that will allow ranching to continue on the largest purchase, the 140,000-acre South Ranch bought in 2012.

But over the long-term, the hundreds of miles of fences that crisscross the patchwork reserve would come down.

The aspirations of the project’s backers stretch beyond just bison. They envision a vast grasslands ecosystem restored to its natural origins — populated with a diverse mix of mule deer, mountain lions, big horn sheep and grassland birds.