Researchers say they now have at least a partial explanation for the decline in the wolf population on Isle Royale in Lake Superior.
Three wolves from the Chippewa Harbor pack were found dead in an old mine shaft on the remote island in early May. According to researchers at Michigan Technological University, they apparently died early last winter. One was a collared male, one may have been an alpha male, and one was a female.
Researchers say it helps explain why the Chippewa Harbor pack did such a poor job hunting last winter. They describe the pack as having no "game plan" after losing so many members.
Researchers say the dead wolves did not seem to be suffering from lack of food.
National Park Service officials say they will investigate safety issues connected with the mine shaft, which dates from the mid-1800s.
The winter survey identified only nine wolves on the island, with apparently only one female.