Date of Award:
Master of Science (MS)
Jessop B. Low
An ecological study on the Morgan Creek and the East Fork of the Salmon River, Idaho, Bighorn Sheep herds was conducted from July 1, 1966 to February 28, 1970.
The Morgan Creek population numbered about 100 animals upon termination of the study. The trend of this population was downward. The East Fork population numbered about 50 animals and the trend appeared to be stable or slightly downward.
Productivity of both herds was low. Lamb mortality was high and recruitment to the breeding herd low. Low recruitment rates coupled with hunting pressure caused a decl ine in the ram component of both herds.
The lungworm-pneumonia complex and scabies mites localized in the ears were common disease-parasite problems for bighorns on the Morgan Creek and East Fork ranges. Poor nutrition was postulated as the reason for endemic disease and parasite problems.
Cougars, coyotes, bobcats and eagles were evaluated as mortaility factors. Evidence did not indicate that any of these were a serious limiting factor. Accidents and poaching also were evaluated as mortal ity factors, but it was not possible to determine the extent to which they contributed to mortality.
Food habits of bighorns and deer were studied on the Morgan Creek winter range. Bighorns were found to use 69 percent grasses, 27 percent browse and 4 percent forbs. The primary grass utilized was Agropyron spicatum 11 anditfie primary browse was Cercocarpus ledifollus.
Considerable competition for forage existed between deer and bighorns. Competition did not occur between bighorns and elk or antelope. Domestic livestock use has converted most of the range in the vicinity of Challis to sagebrush, which is not quality bighorn habitat. Deer numbers have greatly increased because of the habitat change. Livestock now compete with bighorns for the limited amount of remaining grass and deer compete by decimating the mountain mahogany (C. ledifolius. Shortage of protein during the winter is a serious problem for bighorns. Winter range rehabilitation, consisting of sagebrush eradication and accompanied by reduction of deer and domestic livestock usage, is suggested to restore ranges for the benefit of bighorns. Transplanting of bighorns to suitable areas historically inhabited by bighorns is suggested to increase bighorn distribution in Idaho and to stabilize current statewide downward trends In bighorn numbers until winter range rehabilitation problems can be solved.
Breeding occurred in November and December, and lambing in May and June. Twinning did not occur. Several trapping methods were evaluated and a total of 43 bighorns were trapped, Of these, 7 were transplanted, 7 were instrumented with radio transmitters, 23 were neckbanded and 6 accidently killed.
Morgan Creek bighorn sheep migrated an average of 22.4 airline miles to summer ranges. The shortest migration was 19 miles and the longest 28.5 miles. East Fork bighorns were found to migrate about 17 airline mi les to summer range.
Analysis of winter range indicated a canopy coverage of 34 percent for shrubs, forbs and grasses, 42 percent bare soll and erosion pavement and 24 percent natural rock. Forage production was low at 128 to 669 pounds/acre green weight, Big sagebrush contributed 40 percent of the herbage production. Usage on all sites was moderate to excessive. Erosion was very evident, and range condition trend estimated to be downward. Only about 805 percent of the 16,676 acres of winter range within the Morgan Creek study area was quality habitat avai lable to bighorns during most winters. Sagebrush, little used by bighorns, dominated 56 percent of the winter range. Grasses, indicative of quality bighorn habitat, dominated only 17 percent of the winter range.
Idaho's statewide bighorn sheep populations have decreased approximately 50 percent since 1960. Ram components have decreased about 85 percent since 1960. Increased numbers of hunters have harvested fewer rams under the two-week open season 3/4-curl regulation and the point of diminishing returns has begun to operate. Depresslng the ram component below an undetermined level may interfere with reproduction. Therefore, a limited harvest by control led permit regulations and controlled distribution of hunters is recommended.
Morgan, James K., "Ecology of the Morgan Creek and East Fork of the Salmon River Bighorn Sheep Herds and Management of Bighorn Sheep in Idaho" (1971). All Graduate Theses and Dissertations. 1593.
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