DOI: 10.5061/dryad.2bvq83c25
title: Bison population surveys in Yellowstone National Park (USA): 1970-1997

description: 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
 surveys was to locate and count all visible bison, excluding those
 wandering outside population-use areas. A sharp-eyed pilot made the
 initial count of bison and calves, while the observer cross-checked,
 noting group sizes, animal locations, and any significant observations,
 such as mortality or unusual habitat factors. Data were recorded manually
 and later transcribed to field notebooks. Location descriptions were
 converted into UTM coordinates using the 1961 U.S. Geological Survey
 Topographic Map of Yellowstone National Park with a 10 km UTM grid
 overlay.
description: 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 9-10 per year, circumstances permitting, for a total of 151.
 Two surveys were not complete; these were made to verify Pelican area calf
 numbers (flight 3, June 3, 1970) and the Mary Mountain winter-spring
 distribution change (flight 11, May 1, 1972). Flying weather required
 reasonably wind-free, clear-to-partly cloudy conditions. Occasionally wind
 and/ or ground fog over open valleys dictated a survey could not be
 completed in one day, in which case the rest of the areas usually were
 flown the following day. In the data, these pairs of flights were merged
 and considered a single flight. Further, flights usually were broken only
 between the major geographic wintering areas of the northern and central
 regions. There are indications (to be discussed below) that there is
 little population transfer between these areas in general. Also, during
 the earlier years the bison numbers observed on flights over the northern
 range by an elk researcher (D. B. Houston) occasionally were used when the
 timing was suitable, rather than duplicate the effort. Surveys were
 intended to locate all visible bison within the YNP, with the exception of
 wandering bulls that were beyond population-use areas in unknown and
 unpredictable sites. An exceptionally sharp-eyed pilot (D. Stradley) made
 the overall and calf counts. The observer (MM)
 cross-checked and recorded those numbers, locations, groups size and
 cohesiveness, general conditions, and miscellaneous data such as
 mortality, travel routes, and so forth. All initial data entries were
 recorded manually and transferred to field notebooks as soon as possible,
 usually the same day. Over the course of 27 years of data collection, 11
 field journals were cataloged with detailed information concerning seven
 key variables: location, group size, demographics, dispersion, group
 shape, snow cover, and habitat use. Processing the data
 occurred in three major steps. After agreeing on a spreadsheet format,
 data was hand-translated by the original observer (MM) from journal to
 spreadsheet outline. Location descriptions were translated into UTM
 coordinates by the original observer (U.S. Geological Survey Topographic
 Map of Yellowstone National Park, Wyo.-Mont.-Idaho. 1961ed. with 10 km UTM
 grid overlay). Secondly, the data was entered into a computer spreadsheet.
 Upon completion, on December 15, 1998, over 22,000 lines containing 25
 variables had been entered into the data set. Finally, the electronic data
 set was checked and validated as thoroughly as possible. Because of the
 massive size of the data set, several methods of checking were
 implemented. Data transformations looked for spatial continuity in
 observation sequence. Furthermore, each flight was summarized for the
 number of observed bison. All anomalies suggested by the transformations
 and summaries were back-checked to the original observer’s log. Five major
 passes were made to reconcile our computerized data representation with
 all aspects of the aerial surveys recorded in the field notebooks. This
 work was completed on September 2000. The precision of
 the location description translation process was checked for a random
 sample of a hundred and fifteen observations, stratified over the five
 principle localities. For each observation, a maximum deviation from the
 assigned UTM coordinates consistent with the observer’s description was
 determined in both east/west and north/south directions. From these a
 maximum possible error was calculated for each sampled observation. The
 mean maximum possible error was found to be only 0.324 km (s.d. 0.156)
 with no significant difference among localities. Errors of this magnitude
 are inconsequential for all analysis performed in this study. Fig. 32
 plots all bison observations made during the study. The points in this
 figure have radii about 50% larger than the mean maximal error. The second
 pass through the notebooks also gives us a check of our transcription
 accuracy. Of the 230 transcribed UTMs, 229 agreed exactly with the
 spreadsheets. The final UTM had a small discrepancy in trailing digits
 amounting to an error of about a quarter of a kilometer. Errors of this
 magnitude would not be caught by our continuity checks.
description: # 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 dictated a survey could not be completed in one day, in which
 case the rest of the areas usually were flown the following day and the
 data melded for a single flight total. Thus certain flights numbers in the
 data set have observations on two dates.  Also, during the earlier years 
 the numbers observed on the northern range by an elk researcher
 occasionally  were used when the timing was suitable, rather than
 duplicate the effort. Surveys were intended to locate all visible bison
 with the exception of wandering bulls that were beyond the population-use
 areas in unknown and unpredictable sites. An exceptionally sharp-eyed
 pilot made the overall and calf counts. The observer  cross-checked and
 recorded those numbers, group size and cohesiveness, separated animals and
 their locations, and general conditions, Miscellaneous data such as
 mortality, travel routes and timing, unusual habitat factors, etc. were
 noted on occasion. All initial data entries were recorded manually and
 transferred to field notebooks as soon as possible, usually the same day.
 ### Files and variables #### File: YNP\_BISON.csv and YNP\_BISON.xlsx
 **Description:** YNP Bison data in *.CSV file form; YNP Bison data in
 Microsoft Excel form. ##### Variables * ID: Unique identifier (1, 2,
 3....) * MONTH: Month of observation (1=Janunary, 2= February,...12=
 December) * DAY: Day within month the observation was made * YEAR: Year of
 the observation (70=1970, 71=1971,....) * TIME: Approximate time during
 the day the observation was made. * GROUPSIZE: Number of bison in group *
 CALVES: Number of calves per observation (subset of bisontotal) * BULLS:
 Number of bulls per observation (subset of bisontotal) * UNKNOWN: Number
 of bison (sex or stage unidentified) * BISONTOTAL: Summation of all
 individual bison within a given observation (bulls+calves+unknown) *
 COHESION: Measure of distance between animals in group.  1=Cluster tight
 (0.5-3 animals distances); 2=Medium (3-10 animal distances); 3= Loose
 (over 10 animal distances). * GROUPSHAPE: Geometric form of the group
 (1=globular; 2=linear). * HABITAT1: Primary habitat for observation
 space; Habitat includes: 1=Sedge , 2=Upland , 3=Geothermal, 4=Trees,
 5=subalpine, 6=creek/river,7=road, 8=willows, 9=1988 forest burn,
 10=feedground * HABITAT2: Secondary habitat for observation space; Habitat
 includes: 1=Sedge , 2=Upland , 3=Geothermal, 4=Trees, 5=subalpine,
 6=creek/river,7=road, 8=willows, 9=1988 forest burn, 10=feedground *
 HABITAT3: Tertiary habitat for observation space; Habitat includes:
 1=Sedge , 2=Upland , 3=Geothermal, 4=Trees, 5=subalpine,
 6=creek/river,7=road, 8=willows, 9=1988 forest burn, 10=feedground *
 SNOWCOVER: A two dimensional aerial view of snow coverage across a
 landscape.  0=no snow, 1=patch snow (openings on geothermal, south facing
 exposures, and wind swept areas), and 2=snow covered landscapes. *
 EUTM: Map Coordinate east to west. * NUTM: Map Coordinate north to south.
 * LOC$: General location of subset geographical areas of Yellowstone
 National Park including: Northern, Pelican, Hayden, Firehole, and
 Westside.  * FLIGHT: Ranked 1 to 151 by order of year, month, and day. *
 HERD$: Two main heard locations: Northern or Central ## Access information
 Other publicly accessible locations of the data: None Data was derived
 from the following sources: Notebooks of Dr. Mary M. Meagher 1970-1997.