October 19, 2009
Distemper Linked To Yellowstone Wolf Pup Deaths
Since wolves were reintroduced in Yellowstone in the 1990s, there have been significant variations in the size of the Park wolf population. In an article in our February 2009 issue of Yellowstone eNews, we told you that 2008 counts showed a marked decline in the number of wolves in the Park. Now, a new study links canine distemper to last year’s wolf pup deaths and helps explain the decline.
Since wolf reintroduction, there have been three years when the pup survival rate was extremely low: 1999, 2005, and 2008. Canine parvovirus was believed to be the cause of the wolf pup deaths in 1999 and 2005. Wildlife biologists speculated this because parvovirus is known to cause a high mortality rate in domestic dogs, and was suspected in the high death rate of wolves at Isle Royale National Park in Michigan in the early 1980s.
Results of newly published research point to canine distemper as the cause of the low pup survival rates. Over a period of 17 years, researchers took blood samples from wolves and coyotes in Yellowstone National Park, looking for exposure to a number of canine diseases.
The blood test results indicate that some diseases like parvovirus are chronic in Yellowstone’s wild canines. However, signs of distemper appeared only in the years when pup mortality was high. Since distemper weakens the immune system and makes infected animals susceptible to other infections, it can be difficult to determine the actual cause of death.
So what do the results of this study mean for the future of wolves in Yellowstone? According to Dr. Doug Smith, Yellowstone Wolf Project Leader, the population will not likely suffer long-term effects from the 2008 outbreak.
“Our research indicates that the wolf population seems to fare well despite some chronic infections, and rebounds well from periodic exposure to distemper,” said Dr. Smith.
Official counts of the Yellowstone wolf population are generally performed annually in late fall and early winter. By the end of December 2009, there will be an updated population estimate that will help determine the current health status of Yellowstone wolves.
While the research was unable to conclusively determine the episodic source of the canine distemper, data suggest it is not linked to the region’s domestic dog population.
The research was conducted by the Yellowstone National Park Center for Resources, the University of Minnesota, and the nonprofit Yellowstone Ecological Research Center. Funding was provided, in part, by Yellowstone Park Foundation support of the Yellowstone Wolf Project and the Yellowstone Wildlife Health Program.
If you are interested in reading more on this topic, the full findings of the study were recently posted to PLoS ONE, a peer-reviewed online journal that posts reports of original research in science and medicine.