Bison population surveys in Yellowstone National Park (USA): 1970-1997

This study presents data from aerial surveys conducted in Yellowstone National Park spanning from 1970 to July 1997, aimed at monitoring the bison population. Surveys were initially conducted four times per year from 1970 to 1990, with a consistent pilot and observer, weather permitting. In 1991, the frequency increased to 9-10 surveys per year. Ideal flying conditions required clear-to-partly-cloudy skies and minimal wind, typically in the early morning to avoid stronger winds later in the day. The flight path commonly began in the northern range and proceeded sequentially southward, though weather conditions such as wind or ground fog sometimes necessitated route adjustments. In instances where surveys could not be completed in a single day, the remaining areas were surveyed the following day, and data were combined. During the early years, data from an elk researcher were sometimes used for the northern range when timing allowed, minimizing overlap in efforts. The objective of the su..., The study area encompassed most of Yellowstone National Park, USA. Aerial survey efforts concentrated on the locales used by the mixed groups (cows with young, usually some mature bulls). Historically, the winter locales used by bison occupied three areas designated the northern range (Lamar Valley), Pelican Valley, and Mary Mountain. The latter encompassed both the centrally located Hayden Valley and the Firehole to the west as one wintering unit because of the movements in both directions across Mary Mountain.
Beginning in the 1980’s as bison use patterns began to change, the west side was considered as part of the Mary Mountain geographic unit. Because adult bulls may wander widely, extra efforts were not made to locate these scattered individuals. The data span 1970 through July 1997. There were four aerial surveys per year (Piper Supercub, same pilot and observer with few exceptions), weather, and desired timing permitting from 1970 through 1990. Thereafter surveys increased to 9-1..., , # Bison population surveys in Yellowstone National Park (USA): 1970-1997

Dataset DOI: [10.5061/dryad.2bvq83c25](10.5061/dryad.2bvq83c25)

## Description of the data and file structure

# *Collection Metadata*

The data span 1970 through July 1997. There were four aerial surveys per year (Piper supercub, same pilot and observer with rare exceptions), weather and desired timing permitting from 1970 through 1990. Thereafter surveys increased to 9-10 per year, circumstances permitting. Flying weather required reasonably wind-free, clear-to-partly-cloudy conditions park-wide, beginning 0800-0900 usually  to be ahead of the strong winds that often developed later in the day. Surveys most commonly began with the northern range and proceeded sequentially toward the east boundary and upper Lamar, Mirror Plateau and Pelican Valley, Hayden Valley, the Firehole, and the west side. However wind and/or ground-fog over open valleys sometimes required a change of route. The same factors occasionally d...,