How healthy is Yellowstone National Park's wolf population? While wildlife biologists say the wolves overall are doing well and that the recovery program launched in 1995 has indeed succeeded, this past year was tough for the park's keystone predators.
Disease and infighting are being blamed for a drop of more than 25 percent in the numbers of wolves in Yellowstone. While the drop from 171 wolves in 2007 to 124 in 2008, or 27 percent, seems staggering, back in 2005 the numbers showed a slightly greater drop, from 171 wolves counted in 2004 to 118.
Plus, Yellowstone officials say last year's decline was the first drop in wolf numbers in the park in three years.
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.
The number of breeding pairs in the park also declined from 10 to six. This is the lowest number of breeding pairs recorded since 2000 when wolves first met the minimum population requirement for delisting.
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.