Pair of wolves cross to Isle Royale, but they don't stay long
Two wolves took advantage of an ice bridge to travel to Isle Royale National Park from the north shore of Lake Superior last month, but left within a few days, researchers said Tuesday.
No breeding took place during the wolves' five-day foray onto the island, meaning no new genes were introduced to the park's dwindling and inbred wolf population.
A radio collar worn by one of the two wolves showed the pair crossed to Isle Royale on Feb. 22 and left on Feb. 27, about a 14-mile trip one-way, said Rolf Peterson, a Michigan Technological University wolf researcher who followed the wolves' tracks during their visit on Isle Royale. Recent warmer weather means the opportunity for other wolves to cross probably is over for the year, as the ice bridge begins to break up.
The wolves traveled two-thirds of the way up the island from the southwest end before turning around. Before heading back to the mainland, the two newcomers were near a couple of Isle Royale's resident wolves and probably communicated, but didn't breed with the resident wolves, Peterson said. The two wolves also didn't kill any moose while on Isle Royale.
"The wolf population is in poor shape," Peterson said. "It suggests it takes more than an ice bridge to solve that problem."
Isle Royale's wolf population is at its lowest level yet — less than 10 animals were reported last year — due to genetic inbreeding caused by the barrier of Lake Superior keeping the wolf population cut off from wolves on the mainland, Peterson said. Wolves have on occasion crossed the frozen lake between the mainland and Isle Royale — but statistics show the frequency of ice bridges forming also is dwindling.
Ice bridges formed 80 percent of the time in the 1960s, but now are down to about once every five to 10 years, Peterson said.
One wolf crossed onto Isle Royale when an ice bridge formed in 1997, the last time a non-resident wolf mated with Isle Royale's wolf population. The next time an ice bridge formed was in 2008, when two radio-collared wolves left Isle Royale, Peterson said. Last year's bitterly cold winter also brought an ice bridge and one radio-collared wolf left Isle Royale, dying on the mainland.
Although an ice bridge can bring more wolves to Isle Royale, it will take more than that to add new genes to the resident wolf population, said Peterson, who spends eight months of the year on Isle Royale.
Reproduction among the resident wolves has declined in the past four years because the wolves are now in the second generation sired by the immigrant wolf who crossed in 1997, Peterson said. That means that parents and offspring or siblings are breeding, but wolves can't inbreed and be viable, Peterson explained, adding that researchers know all the resident wolves have spinal abnormalities.
The inbreeding has "led to a collapse in the last five to six years," Peterson said.
With so few years with ice forming now, it's up to the National Park Service to figure out what, if any, steps should be taken to help the wolf population and maintain the predator-prey balance between wolves and moose on the island, he said.
Last year the National Park Service opted against an emergency genetic rescue of wolves on Isle Royale by artificially introducing new wolves to the island. Park officials chose to instead conduct a long-term environmental review on the park's diminished wolf population.
Wolves are relatively new to the 45-mile-long, 143,000-acre island complex off Minnesota's North Shore at the Canadian border. The island's first wolves crossed Lake Superior ice to get there in 1949, and their numbers have ranged from a previous low of 11 in 1993 to a high of 50 in 1980.