GRAND CANYON NATIONAL PARK, Ariz. (AP) — Grand Canyon National Park says it's been overwhelmed by the amount of interest in a program to thin a herd of bison using volunteer shooters.

The National Park Service approved a plan last month to decrease the herd through roundups and by seeking volunteers who are physically fit and proficient with a gun to kill the animals.

Park officials say the roughly 600 bison in the region increasingly are damaging park resources.

Grand Canyon spokeswoman Kirby-Lynn Shedlowski says she initially received dozens of calls a day from people across the country wanting to volunteer. Callers now are directed to a recorded line and asked to check back periodically.

The park, state game officials and the Intertribal Buffalo Council are expected to meet this month to begin crafting program guidelines.