Yellowstone wolf numbers decline
by National Park Service press release
January 13, 2009
The number of wolves in Yellowstone National Park declined last year. Itís the first drop in wolf numbers in the park in three years.
The Yellowstone Wolf Project reports the 2008 population at 124 wolves, down 27 percent from the 171 wolves recorded in 2007.
The greatest decline occurred on the northern range, the area with the greatest wolf population density. The wolf population there dropped 40 percent, from 94 to 56 wolves.
The decline in the wolf population in the interior of the park was smaller. That population dipped from 77 to 68 animals, off 11 percent from the previous year.
A similar population decline most recently occurred between 2004 and 2005, when overall wolf numbers in Yellowstone dropped from 171 to 118 animals.
The number of breeding pairs in the park also declined from 10 to 6. This is the lowest number of breeding pairs recorded since 2000 when wolves first met the minimum population requirement for delisting.
The reintroduction of wolves to Yellowstone National Park began in 1995. Wildlife biologists affirm that the Yellowstone wolf population has recovered, and that wolf population numbers can be expected to fluctuate as they do for other wildlife species.
Previous population declines in 1999 and 2005 were attributed to the impacts of disease, especially on wolf pups. This past year, distemper, mange, and wolves killing each other are the likely causes of the population decline.
Distemper is fairly common in wildlife and is believed to be the major contributor to the recent decline in the population of wolf pups in the park. The often fatal virus can be found in and readily transmitted between wolves and other animals such as coyotes, foxes, raccoons, and skunks. Biologists will capture and sample wolves to confirm that distemper is indeed affecting wolves. In 1999 and 2005 distemper was found in both wolves and coyotes.
Mange is a parasitic infection of the skin. It can weaken the animal, making it susceptible to infections and other problems which can lead to death.
Finally, wolves often kill each other over competition for food or territory. Population density could contribute to an increase in wolf-on-wolf mortality.
Multi-year research projects are underway to help wildlife biologists better understand the impacts of disease and of animal social dynamics on wolf population changes.