ROCKY MOUNTAIN ARSENAL WILDLIFE REFUGE, Colo. — The dwindling of open space where bison can roam is hurting federal efforts to restore herds, forcing refuge managers to kill hundreds of bison and search for land links between protected areas.
But the bison on fenced preserves continue to multiply — 11 calves were born here this spring after recent forced herd reductions. Interior Secretary Sally Jewell says she is working on ensuring large landscapes nationwide, increasingly by collaborating with private property owners.
"One of our biggest challenges across the entire country is habitat fragmentation. It certainly has impacted the bison," Jewell said in a recent interview.
"There's almost no animal it has not impacted. You get a treasure like the Rocky Mountain Arsenal National Wildlife Refuge — 15,000 acres in an urban area. It is really an oasis. But without connectivity to other parts of the landscape, it's going to be difficult to make it anything like what it used to be."
Limited open space has forced culling of bison each year from nearly all the Department of Interior's 17 restoration herds — 10,000 bison on 4.6 million acres in 12 states. These include the most genetically robust bison, a third of bison managed for conservation purposes. Of those 17 herds, 11 are fenced-in.
Once numbering 20 million, bison roamed across North American grasslands before they were hunted to near extinction.
Culling means killing through hunting or hauling to tribal land where bison are used for meat and other products. In some cases, federal managers send excess bison to ranchers and zoos.
Beyond the Rocky Mountain Arsenal refuge north of Denver, annual roundups remove up to 1,000 bison a year from the Yellowstone herd and hundreds from Badlands and Wind Cave national parks in South Dakota and Theodore Roosevelt National Park in North Dakota, federal officials said. Scores more are culled from the Tallgrass National Preserve in Kansas and the Chickasaw National Refuge in Tennessee.
By culling bison, federal managers try to prevent degradation of land from overgrazing. A bison can eat up to 50 pounds of grass a day.
Creating land corridors between protected areas looms as a difficult challenge because of population growth and development. Since 2008, federal biologists have been charged with restoring bison nationwide for their cultural and ecological benefits.
Interior Department officials said they're poised to establish new herds on historical bison range. For example, Grand Canyon National Park managers are evaluating options in northern Arizona. Federal wildlife officials also are looking for opportunities to restore "unfenced low-density bison herds" by working with landowners, tribes, states and nonprofit groups in a way that addresses local concerns.
In Colorado, the Rocky Mountain Arsenal herd of 81 bison, confined to 2,600 acres, rebounded this spring after about 18 bison were removed in December. Refuge plans call for increasing the carrying capacity to 250 bison by expanding pastures — but this requires irrigation and fencing. Bison helped draw 300,000 visitors in 2013, up eightfold since 2011.
"The vision is for connectivity," but there are no current plans for creating corridors to eastern prairie, said Leith Edgar, a U.S. Fish and Wildlife Service spokesman.
"The focus right now is on improving habitat for bison within the Rocky Mountain Arsenal. There is limited habitat now, which is why the herd cannot go above 81. There would be no need to cull if there was enough habitat."
Jewell said President Barack Obama is committed to educating communities about bison, reducing fears that bison disease will hurt cattle and building support for connected ecosystems.
"It's important that we share information, look for compatible uses of landscapes and that we look at maintaining connectivity," she said.
Jewell cited efforts to create bison-friendly landscapes at the Crown of the Continent area in Montana and the Yellowstone-to-Yukon campaign to preserve open land between Yellowstone and Canada's Yukon territory. This bi-national effort, which bestows grants, focuses on ensuring safe migration pathways between protected areas for grizzlies, fish, birds and other animals inhabiting the ecosystem.
These create "test areas where there is a lot of support and a lot of science to help us understand what is possible and what we can do," Jewell said.
"Like the bald eagle, the bison is a symbol of the American Great Plains. We all feel, when we see a bison, that we are looking into our history before settlement."