American pronghorn antelope in the Yellow Water Triangle, Montana : a study of social distribution, population dynamics, and habitat use /

Abstract

Excellent descriptions of geology, soils, climate, vegetation, and history ol the study area are provided in Gieseker et al (1953), Cole (1 956), Bayless (1969), and Jorgensen (1979). The following summarizes those accounts while adding details particularly relevant to antelope eeology. Location The Yellow Water Triangle (266 mi^) is near the geographie center of Montana (Fig. 2); 62% of the land area falls within Petroleum County and 38% within Fergus County (Jorgensen 1979). The area is enclosed by U.S. Highway 87 (20 mi from Grass Range to FlatwiUow Road), Montana Highway 200 (23 mi from Grass Range to Winnett), Montana Highway 244 (18 mi from Winnett to FlatwiUow Road), and FlatwiUow Road (5 mi from U.S. Highway 87 to Montana Highway 244). Drainages of two minor permanent streams (FlatwiUow and McDonald Creeks) and three intermittent streams (Pike, Elk, and YeUow Water Creeks) paraUel one another across the study area. The name "YeUow Water" is derived from the discoloration of the stream by yellowish bentonite from certain geologieal formations (Jorgensen pers. comm.). Geology and Soils Relief slopes upward from east to west. AU geologieal formations tilt easterly and thus have lower strata exposed at higher elevations toward the west. Elevations range from 3,000 ft at Winnett to 4,500 ft atop Button Butte in the northwest quarter near Grass Range. The topography varies from flat to gently roUing along an elevational gradient that increases an average of approximately 20 ft/mi along MeDonald Creek between Winnett and Grass Range. Most topographical rehef stems from geological relics of hiUs, buttes, and ridges or stream erosion vaUeys, coulees, and draws cut below the level of the prairie plateau. Most of these topographic relics have immediate elevational changes of less than 100 ft.

Pronghorn habitat suitability in the Texas Panhandle

“…According to the model, much of the pronghorn habitat in District 2 is found within designated herd units with most of the habitat representing areas that are non‐wooded with moderate precipitation and variable levels of agriculture. Dependence of pronghorn on open areas has been documented in previous studies (Buechner , Yoakum , Pyrah , Ockenfels et al , Yoakum et al ). Much of the forage preferred by pronghorn is found in grassland and shrubland communities (Einarsen , Buechner , Wentland , Amstrup , Pyrah ) with little tall shrub and tree encroachment (Buechner , Pyrah , Ockenfels et al , Bright and van Riper ).…”

“…Dependence of pronghorn on open areas has been documented in previous studies (Buechner , Yoakum , Pyrah , Ockenfels et al , Yoakum et al ). Much of the forage preferred by pronghorn is found in grassland and shrubland communities (Einarsen , Buechner , Wentland , Amstrup , Pyrah ) with little tall shrub and tree encroachment (Buechner , Pyrah , Ockenfels et al , Bright and van Riper ). Our habitat model shows a higher HSI in areas with the least amount of woodland and greatest amounts of non‐woody vegetation, whether introduced or native.…”

“…Our habitat model shows a higher HSI in areas with the least amount of woodland and greatest amounts of non‐woody vegetation, whether introduced or native. The overall lack of pronghorn habitat near woodlands is supported by previous studies on pronghorn habitat preference, primarily their avoidance of wooded areas (Wydeven and Dahlgren , Pyrah , Ockenfels et al , Bright and van Riper ). Pronghorn preference of shrublands and grasslands during summer (Bayless , Danvir ), that also tend to have lower vegetation profiles, is also supported by the model (Fig.…”

“…Vegetation composition, which was ranked third by experts, was also present in the MAXENT analysis through the distance to agriculture and distance to woodland variables. Pronghorn prefer areas with low vegetation profiles (Buechner , Pyrah , Ockenfels et al ) and diverse species of native shrubs, grasses, and forbs (Einarsen , Buechner , Hailey , McDonald ).…”

“…Precipitation has a direct relationship to water and forage availability (Buechner , Pyrah , Brown et al ), which, in turn, affects habitat suitability. According to the pronghorn habitat suitability model, importance of precipitation is somewhat varied.…”