From USA Today:

It took a couple of months and thousands of hopefuls to find a quartet that fits the requirements for New Moon‘s wolf pack.

No. 1 on the list: Native American or First Nation ancestry, because their characters belong to the Quileute tribe, based in La Push, Wash., both in the book and in real life.

“They had to have papers that proved their heritage,” says director Chris Weitz, who was the one who insisted on hiring within the community. “And they had to be in good physical shape.”

The Twilight sequel is filming now, and between takes, the actors usually are working out with barbells, doing push-ups or chowing down on steak, Weitz says. “They went through wolf camp together, and they are in constant training. It paid off as a bonding thing for them and helped them to get to know one another. They drove each other to get more buff.”

No amount of weightlifting, however, would allow them to act out the wolf portion of their performances; the beasts are about the size of horses and race around on all fours.