In a promising sign for the effort to restore the ecosystem of Yellowstone National Park, wolves imported in January are already trying to breed. Although the 14 wolves shipped from Canada to Yellowstone are still cooped up in one-acre pens in Yellowstone's Lamar Valley, rangers have observed male wolves attempting to mount female wolves. Biologists had initially doubted the wolves would produce pups this spring because of the stress of their transplant. Pups may still be a long-shot, because not all mating tries are successful, but at least they're now a possibility. Two of the 15 wolves released into the wilderness of central Idaho are keeping close company and may also have mated. Biologists expect to keep the wolves penned until about the end of March or until grizzly bears emerging from hibernation begin casing the wolf pens.