Solar radiation is a potentially important covariate in many wildlife habitat studies, but it is typically addressed only indirectly, using problematic surrogates like aspect or hillshade. We devised a simple solar radiation index (SRI) that combines readily available information about aspect, slope, and latitude. Our SRI is proportional to the amount of extraterrestrial solar radiation theoretically striking an arbitrarily oriented surface during the hour surrounding solar noon on the equinox. Because it derives from first geometric principles and is linearly distributed, SRI offers clear advantages over aspect‐based surrogates. The SRI also is superior to hillshade, which we found to be sometimes imprecise and ill‐behaved. To illustrate application of our SRI, we assessed niche separation among 3 ungulate species along a single environmental axis, solar radiation, on the northern Yellowstone winter range. We detected no difference between the niches occupied by bighorn sheep (Ovis canadensis) and elk (Cervus elaphus; P = 0.104), but found that mule deer (Odocoileus hemionus) tended to use areas receiving more solar radiation than either of the other species (P < 0.001). Overall, our SRI provides a useful metric that can reduce noise, improve interpretability, and increase parsimony in wildlife habitat models containing a solar radiation component.
Dietary comparisons based on fecal analysis of mule deer, elk, bighorn sheep, and cattle using mule deer winter ranges along the east slope of the Rocky Mountains indicated that elk, bighorn, and cattle diets were much more similar to each other than to mule deer diets. The greatest overlap between elk, bighorns, and mule deer occurred during late winter when creeping juniper became an important dietary item for all 3 species. Rank-order comparisons indicate that rankings of items in the graminoid and forb forage classes for diets of the 4 ungulate species were significantly correlated with availability of these items. Correlations between availability and diet rank-order were poor for items in the woody forage class. Differences in the diets of the 4 ungulate species were more pronounced at the forage class level than at the plant species/genus level. Resource management along the East Front of the Rocky Mountains in northcentral Montana is becoming one of the most important land use issues in the state. The lo-km-wide strip where the prairie and mountains meet encompasses winter ranges for wild ungulates summering in the Bob Marshall Wilderness, supports a viable cattle industry, and has recently become the center of intense oil and gas exploration activity. Development of oil and gas reserves in the area could alter the existing relationship between livestock and game species by converting rangeland to well sites, roads, or storage facilities and by increasing disturbance and harvest of native ungulates. To contend with these changes in land use, range mangers will require more precise knowledge of the manner in which native and domestic ungulates use available forage than was necessary in the past. This study compares diets of mule deer (Odocoileus hemionus), elk (Cervus elaphus) bighorn sheep (Ovis canadensis), and cattle from sites where concentrations of native ungulates winter. A partial assessment of dietary selectivity is included. Study Area The study area, located approximately 110 km northwest of Great Falls, Mont. (Fig. l), was characterized by shortgrass prairie intergrading with a narrow foothill region of fescue (Festuca sp.)wheatgrass (Agropyron sp.) grassland and limber pine (Pinusflexilis)woodland/savannah. Mule deer, elk, and bighorn sheep winter along the foothill zone from December through May. Most cattle grazing in the foothills occurs from May through October on private, U.S. Forest Service, and Bureau of Land Management holdings.
SummaryFrom September 1971 to March 1972, Chanler's mountain reedbuck (Redunca fulvorufula chanleri Rothschild) were studied on the Arthur Cole Ranch near Gilgil, Kenya. Observation of groups in a volcanic crater on the ranch revealed a marked adherence to activity (high levels in early morning, low levels during midday and high levels in late afternoon) and daily movement patterns (nights and early mornings on slopes, mid‐day at slope bases, and upslope movement in late afternoon or evening). Weather, time of day and month of observation tended to influence counts of mountain reedbuck in cinder cone areas of the ranch.RésuméDe septembre 1971 à mars 1972, les cobs de montagne de Chanler (Redunca fulvorufula chanleri Rotschild), ont étéétudiés au Ranch Arthur Cole prés de Gilgil au Kenya. L'observation de groupes dans un cratère volcanique de la ferme révèle une régularité nette de l'activité (intense tôt le matin, réduite au milieu du jour et reprenant en fin d'après‐midi) et de l'actogramme quotidien (les nuits et petits matins sur les flancs, au milieu du jour au pied des flancs et sur les crêtes en fin d'après midi et le soir). Le temps, l'heure et le mois d'observation ont une influence sur les comptages de ces cobs de montagne dans les zones volcaniques du ranch.
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