Park rangers have been killing off more than two dozen mule deer that became hooked on junk food left by visitors.

Thirteen deer have been shot to death since early December, and National Park Service rangers had planned to kill about 12 more by the end of this week, said David Haskell, chief of resource management for Grand Canyon National Park.

The deer became hooked on snack food and candy handed out at Phantom Ranch, losing their natural ability to digest vegetation, Mr. Haskell said. He called junk food the "crack cocaine of the deer world."

"They've become in extremely poor health, almost starving to death," he said.

Mr. Haskell said that the muscles of all the deer at Phantom Ranch had atrophied and that the animals were so tame they walked right up to the rangers who shot them.