Winter Habitat Selection by Mountain Sheep

Abstract

During winter 1975-76, 197 observations of groups of wintering mountain sheep (Ovis canadensis) provided data on habitat selection near Thompson Falls in northwestern Montana. Sheep selected against upper elevations, drainage bottoms, upper slopes on ridges, areas with a slope steepness of 10-35%, east and southeast aspects, areas greater than 320 m from steep terrain, and closed forests. Preferences (P < 0.1) were shown for cliffs, areas with slope steepness greater than 80% and closer than 320 m to steep terrain or cliffs, and shrubland-grassland and open forest vegetation types. Adult ram groups were observed at higher elevations (P < 0.05) than ewe-juvenile or young ram groups. Sheep apparently sought warmer elevations throughout the winter. There was general agreement on the selection of habitat as estimated from direct observations and fecal group counts. J. WILDL. MANAGE. 46(2):359-366 The importance of winter range in the welfare of mountain sheep has been expressed by several investigators (Honess and Frost 1942, Smith 1954, Buechner 1960, Oldemeyer et al. 1971, Rutherford 1972). However, the mixture of meterological, topographic, and biotic variables which provide adequate winter range has received limited study. Knowledge of variables selected would provide criteria for selecting transplant sites containing adequate winter range. Rutherford (1972) observed that evaluation of potential transplant sites is complicated because mountain sheep are selective and their habitat requirements are not well understood. Our objectives were to quantitatively describe the habitat used by mountain sheep in winter, identify the selection of sites among those available, and evaluate the preference of mountain sheep for biotic and abiotic environmental variables on winter range. STUDY AREA The Thompson Falls mountain sheep winter range is along the southeast end of the Cabinet Mountains just north of the Clark Fork River midway between Plains and Thompson Falls, Montana (Brown 1974). Poorly developed soils and numerous talus slopes emanating from rugged crags of exposed bedrock cover much of the 1,660-ha study area. The valley floor is at 730 m, with the mountains rising to over 1,800 m in less than 2.4 km with south-southwest exposures predominating. Climate is Pacific maritime and January is the coldest month with temperatures averaging -3.1 C (range -37.8 to 13.3 C). Mean annual precipitation is 57.2 cm with greatest amounts falling during November-January. The winter of 1975-76 was slightly milder than average in severity. Plant communities were bryoids on talus slopes, shrubland-grassland complexes, low to mid-elevation Douglas-fir (Pseudotsuga menziesii)-common snowberry (Symphoricarpos albus) communities, and higher Douglas-fir-mallow ninebark (Physocarpus malvaceus) communities. Major grass species present were bluebunch wheatgrass (Agropyron spicatum), pine reedgrass (Calamagros1 Funded by the National Rifle Association, Wildlife Management Institute, Montana Forest and Conservation Experiment Station, and Montana Cooperative Wildlife Research Unit. 2 Present address: Soil Conservation Service, Roseburg, OR 97470. J. Wildl. Manage. 46(2):1982 359 This content downloaded from 207.46.13.111 on Sun, 22 May 2016 04:21:07 UTC All use subject to http://about.jstor.org/terms 360 WINTER HABITAT SELECTION BY MOUNTAIN SHEEP' Tilton and Willard tis rubescens), and rough fescue (Festuca scabrella). Other important shrubs were Rocky Mountain maple (Acer glabrum), Saskatoon serviceberry (Amelanchier alnifolia), snowbrush ceanothus (Ceanothus velutinus), Lewis mockorange (Philadelphus lewisii), antelope bitterbrush (Purshia tridentata), and common chokecherry (Prunus virginiana).