ROBERT A. GARROTT
Professor Fish and Wildlife Management
Ecology Department--Montana State University
Office Phone: (406) 994-2270 FAX: (406) 994-3190 e-mail: rgarrott@montana.edu
Effects of Winter Range on a Pronghorn Population in Yellowstone National Park, Wyoming
Sylvanna J. Boccadori
The
only population of pronghorn antelope (Antilocapra americana) in
Yellowstone National Park (YNP) has showed a recent drop in numbers from over
500 animals in the early 1990’s to <240 animals since 1995. Concern for the
long-term sustainability of this herd led to an examination of the effects that
the winter range has on the habitat use and demographics of this population.
Radio-telemetry data were collected on instrumented adult does from June 1999
through August 2001. While all pronghorn congregated on the winter range from
December through March, there were 2 distinct segments to this population based
on migratory strategy: a resident herd that remained on the winter range
year-round and a herd that migrated to higher valleys within the Park during the
summer. There was evidence of migration north of YNP as well. The current winter
range is located within the northern range of YNP, just west of Gardiner,
Montana. A portion of it lies outside the Park on private, Forest Service, and
conservation easement lands. Results from logistic regression showed that
pronghorn selected for cover and elevation on the winter range and selected
among cover types. Rabbitbrush (Chrysothamnus spp.) and greasewood (Sarcobatus
spp.) cover types were used more than grassland, while big sagebrush (Artemisia
tridentata spp.) types were avoided. Observational data did not show one
cover type being used more for
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feeding and bedding than other cover types. Microhistological analysis of fecal pellets showed that the majority of pronghorn winter diet was comprised of browse, with rabbitbrush being the most prevalent woody species. Due to heavy browsing by ungulates over the past century, seral species such as rabbitbrush have dominated on the winter range while the vigor of the sagebrush community has declined. Adult doe survival probabilities and fawn: doe ratios for non-migratory pronghorn were lower than those for migratory pronghorn. An evaluation of the relationship between adult mortality and recruitment showed that during this study the resident herd was draining the population while the migratory herd was the source of the limited recruitment that occurred.
Publication In preparation
Funding National Park Service, Yellowstone Park Foundation |
Seasonal ranges of pronghorn in Yellowstone National Park, Wyoming. Overlap exists between the summer and winter range because not all animals migrate off the winter range in the summer.
Cover map of the current pronghorn winter range in Yellowstone National Park. |
