Isle Royale wolves starve as island moose decline

CAPTION: A pack of gray wolves is shown on Isle Royale National Park last month. It's shaping up to be a lean year for wolves and moose on the island. (AP/Michigan Technological University photo)

HOUGHTON (AP) — A significant drop in the moose population on Isle Royale is creating a hunger problem for wolves on the 45-mile-long archipelago in northwestern Lake Superior.

In fact, 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 a pack kill a rival pack’s alpha male from an airplane in January.

The steady decline of moose has put the island’s population at its lowest ebb in the 48 years that biologists have studied the relationship between 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 in a phone interview Wednesday.

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.

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 researchers 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 moose drop-off 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 massive animals, making them easy prey for wolves.

The tick problem eased a bit over 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 doesn’t 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.’’

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