Wolves turn to elk calves for dinner

BILLINGS, Mont. — After two years of preferring bull elk on their winter menu, wolves in Yellowstone National Park have switched back to elk calves, which are easier to kill and more plentiful this year, a new study shows.

An early winter study of the wolves in December showed that they were primarily killing young elk, followed by older females and then bulls, said Doug Smith, Yellowstone’s lead wolf biologist.

“My guess is it was just a super mild fall and early winter. When things are mild, wolves don’t have an edge — and the easiest to kill are calves,” Smith said.

Calf numbers have also been up, so more of them were available for predators, Smith said.

On the park’s Northern Range, where more than half the park’s wolves live, about 75 percent of the wolf kills were calves, while 15 percent were bulls and 10 percent were females.

“Prime age” elk were the least frequently killed, Smith said.

Last year, a layer of hardened snow and ice kept food out of reach for many elk and bison. With limited food, they weakened and were easier prey for wolves, who also fed on bull elk in 2004. Wolves fed primarily on calves over the previous nine winters.

Wolf biologists survey the population every December and March to get a feel for what they’re eating and how the overall population is faring.

There were a record 174 wolves in the park in 2003. Disease trimmed those numbers to 118 in 2005.

“They bounced back this year,” Smith said.

Of the 75 pups born in 2006, 60 survived to December. There are now an estimated 136 wolves in 13 packs in the park.

The Northern Range, which is only about one-tenth of the park, has about 75 wolves in seven packs, up from 54 wolves last year but below the record high of 100. There are six packs in the interior of the park. The largest is the Delta pack, with 16 members.