The howls of two, maybe three, pups have joined those of the other eight wolves on Isle Royale — proof of new life for the famous but dwindling packs of predators.

Rolf Peterson, a researcher who's been tracking the wolves for several decades, said he heard the new voices on July 3 while at a campground on the west end of the island. The next morning, he saw small tracks alongside those of the three adults that occupy that end of the national park.

"I was surprised," he said Friday. "It was nice to hear them."

The births signal a remarkable resilience for the wolves, whose numbers have fallen to their lowest point since they were first counted, in 1959. Peterson and other wolf experts fear that, because the animals are the descendants primarily of two wolves, they may all be too closely related.

The event also provides some breathing room for what could be a precedent-setting decision by the National Park Service on whether to introduce new wolves to the island in order to preserve the critical balance between the predator and their primary prey, moose.

"It is always exciting when we learn about successful reproduction of wildlife in the park, and the birth of two wolf pups is especially good news," said park superintendent Phyllis Green. But, she added, "We are still concerned about the population."

The number of wolves on the island in Lake Superior has dropped from 24 in 2009 to eight last spring, which are split into two packs — one at each end of the island — and two loners.

The population took a particularly severe hit in the winter of 2011-12, when three wolves fell to their deaths in one of the many abandoned mine pits on the island, including a young female and an alpha male. Peterson and his co-researcher John Vucetich, both from Michigan Technological University, described those deaths as catastrophic. Then, for the third time in the history of the study, there were no pups born that spring.

The new pups belong to the west end pack, said Peterson. Their parents are a four-year-old male and a three-year-old female, who were each born to different packs. Peterson said wolves tend to seek mates from packs other than their own.

Now the young wolves have to survive the fall and winter, the most difficult time for them to find food — primarily a diet of moose calves and blueberries. The calves, which are a main source of food in spring and summer, are big enough by autumn to be harder to kill, and they can still escape into the water.

"Wolves have gotten the easy ones already," Peterson said.

Beavers, a secondary source of food in winter, can hide in the water until ice forms, around October.

But once winter comes, then even the adult moose are hampered by deep snow and are vulnerable to wolves on the frozen lakes.

If the pups survive their first winter, their chances are as good as those of any adult wolf, Peterson said.

Their arrival adds a new twist to the ongoing debate among National Park Service officials and wolf experts about whether to embark on a precedent-setting "genetic rescue" of the wolves. That would involve artificially introducing one or more new wolves to the island — a decision to interfere with natural processes that could have far-reaching implications for wildlife management at other national parks as well. Some say that the wolves will prevail; others say that even if they don't, it's best to let nature determine the outcome.

"They are in good position to start breeding again and repopulate the island," said Dave Mech, a wolf expert with the U.S. Geological Society in Minnesota. "I don't think they should interfere. Let's see what happens."

Peterson, who advocates bringing new blood into the packs, said the birth of the puppies does not persuade him that the wolves are safe from extinction. They are still not reproducing at rates that would be normal, he said.

"But at least they haven't shut down completely," he said.