The annual summer census of bison in Yellowstone National Park shows there are roughly 3,300 bison in the park's two main bison herds, a number that is up a bit from a year earlier but far below the nearly 5,000 bison counted four summers ago.
Yellowstone officials based the population estimate on a series of aerial surveys conducted in June and July.
The population now includes 2,800 adult and yearling bison, and 500 calves of the year, the park reported Friday. The population is about equally distributed between the Central Interior and Northern Range herds. The population was estimated at 3,000 bison last summer; and at 2,900 adult and yearling bison in late winter. The peak population estimate of 4,900 bison was recorded the summer 2005, said the park.
While much has been made about bison management in the park, particularly about the hazing of bison that leave the park in winter and spring for traditional wintering and calving grounds, Yellowstone officials say the observed rate of population change this past year is within the natural range of expectation for wild bison. The rate at which wildlife populations increase in abundance is a reflection of the combined effects of reproduction and mortality, and is heavily influenced by age structure of the population, and habitat conditions encountered over the course of time, they said.
This population estimate is used to inform adaptive management strategies under the Interagency Bison Management Plan (IBMP). Specific management actions may be modified based on expected late winter population levels as corroborated by the summer population estimate.
The IBMP is a cooperative plan designed to conserve a viable, wild bison population while protecting Montana’s brucellosis-free status. The five cooperating agencies operating under the IBMP are the National Park Service, the U.S. Forest Service, the Animal and Plant Health Inspection Service, the Montana Department of Livestock, and the Montana Department of Fish, Wildlife and Parks.