Yellowstone's wolves in decline

By Corey Binns

It was not a good year for Yellowstone’s wolves. Of the 69 pups born in the park during 2005, only 22 survived. Canine parvovirus, usually found in domestic dogs, is the likely culprit for the biggest population drop in the 11 years since wolf reintroduction. In 1999, the population pulled through a suspected parvo outbreak, but pup survival was 40 percent then, far better than last year’s number. Parvo immunity is passed along in the mother’s milk, but once pups stop nursing, they become vulnerable.

The hardest hit packs inhabit Yellowstone’s Northern Range, where only 8 of the 49 pups survived. "It’s shocking," says Yellowstone Wolf Project Leader Douglas Smith (see "Yellowstone’s Heroine Wolves," February 2005). In the northern areas, the wolves live closer together, which helps spread parvo. Plus, a road goes right through the region, providing easy access for domestic dogs and the virus. Smith says a pet dog probably brought parvo to Yellowstone. The virus lasts up to five years in the soil and spreads easily—an animal can become infected just by sniffing contaminated scat. Laws require park visitors to pick up after their dogs, but not everyone does.

Most research shows that, over the long-term, parvo does not hurt wolf populations. However, Smith speculates that the future may be bleak for Yellowstone’s well-protected wolves because their social system differs from that of other wolf populations. In the park, he’s seen a few older animals live to exert a strong influence over the pack. "Seven- and eight-year-old matriarchs are calling the shots," says Smith. At the current population level, the wolves will have a chance to recover, he predicts, because the virus tends to be episodic. But the loss of so many individuals from one generation concerns him. Seven years from now, the wolves’ social system may suffer from a lack of matriarchs. By killing off so many pups, the parvo outbreak may just have reduced the pool of potential pack leaders of tomorrow.

Wildlife Conservation Magazine