Wolf numbers in Yellowstone National Park declined for the second consecutive year. The decline was expected and considered natural.
The Yellowstone Wolf Project reports the 2009 population at about 58 wolves,
15 percent from the previous year. This is the fourth
decline since wolf reintroduction began in 1995. A population high of 174
wolves was recorded in 2003. In 2004 and 2007, 171 wolves were counted.
Population declines in 1999, 2005, and 2008 were associated with the
disease distemper. So far there is no evidence that distemper was the
cause of the 2009 decline. Probable causes for this last decline were
wolves killing each other, malnutrition, and mange.
The greatest decline occurred on the northern range, the area with the
greatest wolf population density. Wolf numbers there dropped 29 percent,
from 56 to 40 wolves.
The decline in the wolf population in the interior of the park was smaller.
Those numbers dipped from 77 to 68 animals, off 11 percent from the
The number of breeding pairs in the park remained the same at 6. This is
the lowest number of breeding pairs recorded since 2000 when wolves first
met the minimum population requirement for delisting. A "breeding pair" is
defined as a male and female with 2 surviving pups. Poor pup survival, due
primarily to disease, has kept that number low.
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.
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.