Re-introduction efforts include the use of radio collars for tracking.

It was wearing a radio collar at the time.

Three years ago, for instance, crews placed radio collars on many elk in the park.

Now, half a year later, he was trying to trap another wolf to attach a radio collar.

"You wanted to fit them with radio collars," Hammond said.

Han held up a device that looked like a radio collar for a big dog.

He tossed the radio collar in the back of the truck and slid behind the wheel.

Only a single animal has been killed since the herd was equipped with radio collars.

Until the advent of the radio collar 30 years ago, migrations were largely hidden from view.

Other wolves in Montana have ordinary radio collars so researchers can keep track of them.