Wolves are notoriously difficult to observe and follow in most places. This was the first time scientists have been able to measure how successful individual wolves were at hunting, year after year.

The study revealed that wolves reach their hunting peak at age 2 or 3, even though the animals live for an average of five or six years and sometimes reach age 10 or even older.

Packs with a larger proportion of older wolves killed fewer elk than did more youthful packs. Scientists have long assumed that one adult wolf would be as dangerous as the next.

"The take-home message is that an adult wolf is only maximally lethal for about 25 percent of its adult life span," said MacNulty, whose study appeared in the journal Ecology Letters. "Carnivores simply aren't as ferocious as we think they are."

Considering differences among individual wolves can add nuance to the way scientists think about an entire wolf pack and its ability to affect the ecosystem, said John Fryxell, an ecologist at the University of Guelph in Ontario. Given what we know about aging in general, he added, the findings aren't totally surprising.

"Would you be surprised if an 80-year-old didn't win a marathon and wouldn't be the most likely survivor in a plane crash?" Fryxell asked. "It's exactly what you'd expect, but the fact is, people have not necessarily looked for it (in wolves)."

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