Glacier National Park officials have suspended a study of mountain goats after two animals struck by tranquilizer darts died, the Associated Press has reported.

Amy Vanderbilt of the National Park Service says a dart punctured the rib cage of one mountain goat Tuesday, causing respiratory arrest.

Researchers met with park officials Wednesday and were allowed to resume their study. But another mountain goat died after being darted Thursday.

Vanderbilt says that cause of death is not yet known because the carcass hasn't been recovered.

She says park officials decided to suspend the research permits until they can determine what went wrong.

The three-year study on how climate change affects mountain goats is being conducted by the Wildlife Conservation Society and the University of Montana.