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1950-1979

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https://hdl.handle.net/10217/100535

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Browsing 1950-1979 by Subject "Animal ecology"

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    ItemOpen Access
    Summer ecology of bighorn sheep in Yellowstone National Park
    (Colorado State University. Libraries, 1968) Woolf, Alan, author
    A study of the summer ecology of bighorn sheep was conducted in Yellowstone National Park, Wyoming, from June 1966 to September 1967. Study objectives were to census the bighorn population, map the summer distribution, determine summer herd structure and behavior, observe daily feeding habits, and determine the effects of competition on summer ranges. The minimum number of bighorn summering in Yellowstone Park is 558. There were seven main summer herds: the NE herd, the lower Yellowstone and North park herd, the Washburn-Canyon-Specimen herd, the Gallatin herd, the NW herd, the East boundary herd, and the Bechler herd. Most summer range was in the northeast part of Yellowstone Park. Migrations to summer ranges was incomplete in some cases, and the sheep displayed tolerance for a variety of summer habitats. Ewe herd (includes yearlings):lamb ratios were 100:59 in 1966 and 100:48 in 1967. The 1967 ewe:yearling ratio of 100:28 indicated favorable yearling survival from 1966. Grasses, grass-like plants, and forbs formed the bulk of the summer diet. Carex hepburnii was the dominant plant on subalpine summer ranges and was the staple food throughout the summer. In one study site, grasses made up 80.9 and forbs 19.1 per cent of the diet. Interspecific competition was negligible during the study, but potential competition exists between bighorn and elk for space. The greatest potential danger on summer ranges may be intraspecific competition resulting in reduced tolerance to diseases and parasites.
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    ItemOpen Access
    Winter ecology of bighorn sheep in Yellowstone National Park
    (Colorado State University. Libraries, 1966) Oldemeyer, John Lee, author
    A bighorn sheep study was conducted on the northern winter range of Yellowstone National Park, Wyoming from June 1965 to June 1966. The objectives of the study were to census the bighorn population, map the winter bighorn distribution, determine plant composition and utilization on important bighorn winter ranges, observe daily feeding habits, and assess the effect of competition on bighorn sheep. Two hundred twenty nine bighorn sheep wintered on the northern winter range. These herds were located on Mt. Everts, along the Yellowstone River, on Specimen Ridge, and along Soda Butte Creek. The ewe to ram ratio was 100:78, the ewe to lamb ratio was 100:47, and the ewe to yearling ratio was 100:20. Range analysis was done on MacMinn Bench, Specimen Ridge, and Druid Peak. Range condition was best on Specimen Ridge and poorest on Druid Peak. Grass utilization varied from 50 per cent on MacMinn Bench to over 80 per cent on one key area on Druid Peak. Browse utilization was over 60 per cent throughout the winter range. Grasses made up 61.4, forbs 17.2, and shrubs 21.5 per cent of the bighorn's diet. The most important forage plants were bluebunch wheatgrass (Agropyron spicatum), Idaho fescue (Festuca idahoensis), phlox (Phlox sp.), Douglas rabbitbrush (Chrysothamnus viscidiflorus), and winterfat (Eurotia lanata). Competition between elk and bighorn sheep was mild during the study. Because of lighter than normal snowfall, elk were not forced to occupy bighorn winter ranges. Competition with elk was greatest on Specimen Ridge, where over 200 elk spent most of the winter.