FLAGSTAFF, Ariz. (AP) -- Day three and the shooters were waiting under the cover of pine trees for the rain to let up. Thirty minutes later, a single branch snapped, revealing a small herd of bison in the distance.
Before a young cow was identified as the target, the massive animals disappeared into a thicket at the Grand Canyon's North Rim.
"No shots and no bison," said Charles Gorecki, one of about a dozen volunteers selected to participate in a highly anticipated and highly criticized lethal removal program at the Grand Canyon.
Gorecki and the rest of his crew came up empty-handed after a week that required shooting proficiency tests, safety training and walking at least 30 miles (48 kilometers) in elevations that can leave flat-landers short-winded. Three other groups fared better, shooting and field dressing a total of four bison.
Up to 500 bison are roaming the far northern reaches of Grand Canyon National Park, trampling archaeological and other resources and spoiling the water, park officials say. Hunting pressure on the adjacent national forest has pushed most of the animals into the park.
Critics say rather than killing the bison, the animals should be relocated to other areas or given to Native American tribes under an existing effort.
Lethal removal was one of the tools outlined in a 2017 plan approved after an environmental review, but the guidelines weren't established until more recently with the pilot program this fall.
More than 45,000 people applied in a lottery for 12 spots to help cull the herd and make bison less comfortable at the park. One person backed out and another failed the shooting proficiency test, leaving 10 volunteers from around the U.S. working to kill up to 10 bison.
"We were following bison and trying to find bison and disturbing bison by the mere fact of trying to remove them," said Grand Canyon wildlife biologist Greg Holm, who was among most of the crews. "So they had some activity this fall that I don't think they've ever experienced in the park."
As big as they are, they skillfully evaded most of the shooters.
"It was still a learning experience for all of us involved," said Gorecki, a military veteran who works at the University of North Dakota in Grand Forks. "We got an appreciation that they are very quiet and cunning. These animals, if they catch wind of us from hundreds of yards (away) in thick forest, you'll never ever see them. These are not big, fluffy forest cows."
Each volunteer selected up to three people who were on standby to help cut up the bison and pack the meat out. The groups that shot a bison divided the meat and donated parts of the animals to the Navajo and Zuni tribes in Arizona and New Mexico, Holm said.
A crew led by the National Park Service killed one bison in a trial run in August. The meat was given to the Kaibab Band of Paiute Indians, Holm said.
Officials at the Grand Canyon haven't put a price tag yet on the program, but Holm said some of the cost is for overtime pay for park employees. They'll meet soon to determine whether to do it again, he said.
Various groups pushed the park service to call off what they argued is a hunt and suggested relocating the bison to southern Colorado instead. Hunting is prohibited within national parks, but the agency has authority to kill animals that harm resources using park staff or volunteers.
Olympic National Park in Washington state turned to volunteers to reduce the number of mountain goats, and Rocky Mountain National Park in Colorado and Theodore Roosevelt National Park in North Dakota used volunteers for help with elk.
Bison were introduced to northern Arizona in the early 1900s as part of a crossbreeding experiment. The state manages the animals that can be hunted nearby in the Kaibab National Forest.
The main tool in reducing the population at the Grand Canyon has been to corral them near the North Rim entrance and ship them to Native American tribes through the Intertribal Buffalo Council. The park has relocated 124 over the past three years -- enough to start seeing the reproductive rate slow, Holm said. The goal population is around 200.
"Ideally, the more females we can ship out, the better," he said. "But we also do the dance around not wanting to shift away a bunch of females because they have the knowledge to teach the younger generation."
The Modoc Nation in Oklahoma received 16 of the bison last year.
"It's great for us, it's great for our heritage, and they're beautiful animals," said Charlie Cheek, assistant to tribal Chief Bill Follis. "We enjoy working with them, and they're good for our tribe."
The Santee Sioux Nation in Nebraska received 23 bison from the Grand Canyon this year. The Cherokee Nation got 13 that boosted the herd at a tribal ranch in Kenwood, Oklahoma, to more than 200, said Principal Chief Chuck Hoskin Jr. Bison have been an essential source of food, clothing, shelter and tools for tribes and used in ceremonies, he said.
"These newly acquired bison will help revive some ancient cultural traditions, as well as provide expanded economic opportunities for future generations of Cherokee," he said Wednesday.