Grand Canyon National Park, Ariz. – AP –

Park rangers are killing off some two dozen mule deer that have become hooked on tourists' junk food, which an official called the "crack cocaine of the deer world."

The Cheetos, Fritos and candy handed out at Phantom Ranch cause the deer to lose their natural ability to digest vegetation, said David Haskell, chief of resource management for Grand Canyon National Park.

Thirteen animals have been shot to death since early December, and National Park Service rangers plan to kill about 12 more by the end of the week, Haskell said.

"They've become in extremely poor health, almost starving to death," he said. "All the deer at Phantom Ranch are so far atrophied muscular-wise."

The animals are so tame that they walk right up to rangers, who then shoot them.

An animal rights group said the Park Service could have prevented the problem by enforcing regulations against feeding wildlife.

"What they're doing essentially is getting rid of their mistakes," said D.J. Schubert, director of investigation of the Fund for Animals. "The deer should not have to pay with their lives."

The. Park Service said it will increase its education program to stop visitors from feeding animals.

The ranch, which serves food and offers lodging, is a popular destination for people who travel to the canyon's bottom by mule. Pesky deer loiter around the concession stand and the campgrounds, begging for treats.

"Once they get this sugar and salt they develop these extreme addictions, and they can't resist it," Haskell said. "They'll go to great lengths to get this type of food."