DENVER — An argument over whether wolves should be returned to Rocky Mountain National Park to reduce an overabundance of elk is moving to a federal appeals court.

The 10th U.S. Circuit Court of Appeals in Colorado will hear arguments in the case Thursday.

The park sometimes has so many elk that they overgraze the trees, shrubs and grass, leaving other animals without enough food and habitat. The park uses National Park Service personnel and trained volunteers to periodically shoot and kill a specified number of elk.

WildEarth Guardians sued in 2008, saying officials didn't fully consider reintroducing wolves to prey on elk. The group also said using volunteers to shoot elk amounts to hunting, which is prohibited in national parks.

A district court judge rejected the claims and WildEarth Guardians appealed.

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  • This image provided by the Rocky Mountain National Park, Colorado shows some wildlife inside the park Wednesday Oct. 26, 2011. A snowstorm moved in to the area on Tuesday night, dumping 12 to 16 inches of snow. (AP Photo/Rocky Mountain National Park)

  • This image provided by the Rocky Mountain National Park, Colorado shows an elk standing inside the park Wednesday Oct. 26, 2011. A snowstorm moved in to the area on Tuesday night, dumping 12 to 16 inches of snow. (AP Photo/Rocky Mountain National Park)

  • Trail Ridge Road Opens In Rocky Mountain National Park

    ROCKY MOUNTAIN NATIONAL PARK - MAY 23: Alex and Deborah Gibson (L) of Estes Park, Colorado and Dick and Shirley Eakinas of Winnsboro, Texas toast the opening of the Trail Ridge Road and Enos Mills, the park's earliest proponent with champagne May 23, 2003 in Rocky Mountain National Park, Colorado. The road was opened for the season May 23 after crews spent a month plowing through the 15-foot-deep snowdrifts. Rising to an altitude of 12,183 feet above sea level the road is the highest contiguous paved highway in the country. The park is anticipating It's third busiest weekend, next to the Fourth of July and Labor Day. (Photo by Kevin Moloney/Getty Images)

  • Trail Ridge Road Opens In Rocky Mountain National Park

    ROCKY MOUNTAIN NATIONAL PARK - MAY 23: Tourists travel along Trail Ridge Road Road May 23, 2003 in Rocky Mountain National Park, Colorado. The road was opened for the season May 23 after crews spent a month plowing through the 15-foot-deep snowdrifts. Rising to an altitude of 12,183 feet above sea level the road is the highest contiguous paved highway in the country. The park is anticipating It's third busiest weekend, next to the Fourth of July and Labor Day. (Photo by Kevin Moloney/Getty Images)

  • Trail Ridge Road Opens In Rocky Mountain National Park

    ROCKY MOUNTAIN NATIONAL PARK - MAY 23: Ranger Diane Hen explains the biology of Rocky Mountain Elk as tourists spy for the animals May 23, 2003 in Rocky Mountain National Park, Colorado. The park is anticipating It's third busiest weekend, next to the Fourth of July and Labor Day. (Photo by Kevin Moloney/Getty Images)

  • Trail Ridge Road Opens In Rocky Mountain National Park

    ROCKY MOUNTAIN NATIONAL PARK - MAY 23: Francine Weber (L) of Columbus, Ohio and Tony Chamberlain of Urbana, Ohio walk along piles of snow on Trail Ridge Road Road May 23, 2003 in Rocky Mountain National Park, Colorado. The road was opened for the season May 23 after crews spent a month plowing through the 15-foot-deep snowdrifts. Rising to an altitude of 12,183 feet above sea level the road is the highest contiguous paved highway in the country. The park is anticipating It's third busiest weekend, next to the Fourth of July and Labor Day. (Photo by Kevin Moloney/Getty Images)

  • Trail Ridge Road Opens In Rocky Mountain National Park

    ROCKY MOUNTAIN NATIONAL PARK - MAY 23: Cars drive down the Trail Ridge Road May 23, 2003 in Rocky Mountain National Park, Colorado. The road was opened for the season May 23 after crews spent a month plowing through the 15-foot-deep snowdrifts. Rising to an altitude of 12,183 feet above sea level the road is the highest contiguous paved highway in the country. The park is anticipating It's third busiest weekend, next to the Fourth of July and Labor Day. (Photo by Kevin Moloney/Getty Images)

  • Trail Ridge Road Opens In Rocky Mountain National Park

    ROCKY MOUNTAIN NATIONAL PARK - MAY 23: Danny Basch, of Estes Park, Colorado packs his daughter Annalise, 2, for a ski run above Trail Ridge Road May 23, 2003 in Rocky Mountain National Park, Colorado. The road was opened for the season May 23 after crews spent a month plowing through the 15-foot-deep snowdrifts. Rising to an altitude of 12,183 feet above sea level the road is the highest contiguous paved highway in the country. The park is anticipating It's third busiest weekend, next to the Fourth of July and Labor Day. (Photo by Kevin Moloney/Getty Images)

  • Trail Ridge Road Opens In Rocky Mountain National Park

    ROCKY MOUNTAIN NATIONAL PARK - MAY 23: People walk near the Trail Ridge Road May 23, 2003 in Rocky Mountain National Park, Colorado. The road was opened for the season May 23 after crews spent a month plowing through the 15-foot-deep snowdrifts. Rising to an altitude of 12,183 feet above sea level the road is the highest contiguous paved highway in the country. The park is anticipating It's third busiest weekend, next to the Fourth of July and Labor Day. (Photo by Kevin Moloney/Getty Images)