Last winter, Isle Royale wolf researchers reported a stunning decline in the island's wolf population -- from 16 to nine in one year, leaving only one known female.
Now they know why.
The researchers reported Thursday that they found the bodies of three adult wolves in an abandoned mine shaft. One was a young female -- the island's second female, who could have played a critical role in the pack's survival.
John Vucetich, one of the researchers and a biologist at Michigan Technological University, described the three deaths as a catastrophe. One wolf was a collared male the researchers have been unable to locate since winter; the second was an older male who was probably the alpha male of the pack; the third, a young female born in 2011.
Vucetich said researchers don't know how the wolves fell into the pit, but guessed that snow and ice played a role.
The find clarifies the sudden decline in the island's wolf numbers and may explain the "desultory pattern of travel and low kill rate in this pack," Vucetich said. The pack seemed to have no "game plan" following the large loss of so many individuals.
The collared wolf was nicknamed Romeo because of his eagerness to mate.
The female was lost at a critical juncture in the wolves' history. The shortage of females means the wolves, which have been on the island in Lake Superior since the 1950s and have been closely studied for insights into the survival of isolated animal populations, may well go extinct. There is one other known female on the island. The scientists believe she has mated, but won't know if she's pregnant until they get a glimpse of pups later this summer.
The National Park Service and wolf researchers across the country are now debating whether to bring new wolves to Isle Royale to replenish the pack or let nature take its course -- a precedent-setting decision for management of the nation's wildest places.
As for the mine shaft, it dates to the era of the Pittsburgh and Isle Royale Company, which operated in the Todd Harbor area between 1846 and 1853.
"Random events often play a large role in isolated, island populations, and although tragic, information from this event will ... help us evaluate future management of this population," said Park Superintendent Phyllis Green.