Yellowstone National Park’s bison population is estimated to be 3,700 bison following the park’s annual summer survey — down from last year’s count of 3900. The estimate is based on a series of aerial surveys. Specifically, there are an estimated 2,300 bison on the Northern Range this summer, with 1,400 in the Central Interior herd. Winter mortality, the report goes on, was estimated at 500 bison while there were 583 calves-of-the-year observed in a June aerial survey. The peak bison population estimate was recorded in the summer 2005 when 5,000 bison were estimated to be roaming the park. Spokesman Al Nash says the observed rate of population change this past year is within the natural range of expectation for wild bison. Nash says the population estimate is used to inform adaptive management strategies under the Interagency Bison Management Plan.