TRAVERSE CITY, Mich. Gnawing leisurely on the remains of a moose carcass, the wolf pack's alpha male seemed unaware that mortal danger was coming ever closer.
Suddenly the eight-member rival pack burst into view. The alpha scrambled to his feet, but too late. Howling and barking, the enemy chased him down and mercilessly attacked, killing the hapless victim within a couple of minutes.
It's not unusual for the gray wolves on Isle Royale National Park to target each other, said John Vucetich, a Michigan Tech University wildlife biologist who witnessed the carnage from an airplane in January. But the rival pack's brazen invasion of another's territory was a sign the wolves are hungry. The reason is a steady decline of moose, now at their lowest ebb in the 48 years that scientists have studied the two species in Isle Royale's closed environment.
"One of the ways the wolves struggle through a food shortage is to try and usurp territory from their neighbors," Vucetich said.
He and fellow researcher Rolf Peterson estimated the moose population at 450 this winter, down from 540 last year. Only four years ago, they totaled an abundant 1,100 in the national park, located in northwestern Lake Superior and accessible only by boat or airplane.
Meanwhile, the wolf census held at 30 for the second consecutive year. But their numbers are sure to drop because there won't be enough moose to feed them all, the scientists said. Presently, there are about 15 moose for every wolf. The normal ratio is 40 to 50 moose per wolf.
"The bulk of the moose population at any point is invulnerable to wolves, because they're young and vigorous enough to fight off the wolves," Peterson said. Wolves feast mostly on calves and elderly moose, both of which are in short supply, he said.
The population decline results in part from the aging of a "baby boom" generation dating from the early 1990s, when wolf numbers plummeted because of a parvovirus outbreak, he said. Also, a tick infestation in recent years weakened the animals, making them easy prey for wolves.
The tick problem eased during the past year but remains a threat. Another is a gradual decline of the moose's primary food supply as the island's forests evolve from primarily birch and aspen to less nutritious spruce and balsam fir, Vucetich said.
The changing forest cover has caused a sharp drop in beaver, an alternative food source for wolves, Peterson said.
The moose's historic low does not mean it is in any danger of disappearing, he said. Its decline will enable vegetation to recover from overbrowsing when the herd was thriving, and fewer will be killed as wolf numbers inevitably fall.
"One-third of the kills this winter were calves," Peterson said. "The wolves need to go down to give more calves a chance of reaching adulthood."
Most of the park's 30 wolves belong to one of three packs. But one of them, dubbed the Chippewa Harbor pack, is in danger of disintegrating after losing its alpha male and valuable turf to the rival East Pack, Vucetich said.
The Chippewa Harbor pack is "done for" if it fails to find a strong replacement for the alpha male and loses its alpha female, he said.
"The others would disperse. Some would join other packs, some would starve," Vucetich said. "It's a live by the sword, die by the sword kind of thing."