Since most of the Nez Perce pack are still in the pen, recapturing the stray is not Bangs' top priority.

CNN: Wolves' return to Yellowstone sparks controversy

The Nez Perce pack was released in April 1996, and immediately lost "pack unity, " the National Fish and Wildlife Service said.

CNN: Wolves' return to Yellowstone sparks controversy

As biologists and rangers approach the Nez Perce pack's chain-link pen deep in the park's interior, they hear a surprising sound -- a wolf barking from outside.

CNN: Wolves' return to Yellowstone sparks controversy