Efffects of winter recreation on bighorn sheep

Authors(s): K. Legg

Publication: Effects of winter recreation on wildlife of the Greater Yellowstone Area: a literature review and assessment. Report to the Greater Yellowstone Coordinating Committee. Yellowstone National Park, Wyoming.

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Publication Date: 0000-00-00

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Abstract: POPULATION STATUS AND TREND Bighorn sheep (Ovis canadensis) were historically found throughout the mountains of western North America. Prior to the arrival of European man, their population is estimated to have been between 1.5 and 2 million. Bighorn sheep numbered fewer than 42,000 in 1974 (Wisthart 1978 in Reisenhoover et al. 1988). This decline was caused by competition with livestock, introduction of diseases, hunting, and loss of habitat during European settlement of the West (Buechner 1960, Keating 1982). With the establishment of management areas and hunting regulations, bighorn sheep have reoccupied some of their historic ranges, although populations have not reached pre-settlement sizes. The creation of Yellowstone National Park in 1872 provided needed protection for the Rocky Mountain bighorn. In the early 1900s, fewer than 150 bighorn sheep were thought to exist in Yellowstone, and by 1912 managers estimated that 200 bighorns were in the park (Seton 1913, Mills 1937). Presently, bighorn sheep are found in limited areas of suitable habitat throughout the Greater Yellowstone Area (GYA); estimates of their numbers are included in Table 1 (see online source). Larger populations are found along the eastern boundary of Yellowstone, with some populations having more than 1,000 animals. Today, bighorn populations continue to have some of the same problems that bighorns had when European settlers first arrived. In the winter of 1981?82, a chlamydia (a contagious infection of the eye) outbreak on the Mt. Everts winter range in Yellowstone reduced the bighorn population by more than 50 percent, from 487 to 159 (Meagher et al. 1992, Caslick 1993). Since that time the bighorn population has increased only slightly, and in 1996, 167 bighorns were observed on the same winter range surveyed before the outbreak (Lemke 1996). Other populations in the GYA have declined as well (Jones 1994; Legg 1996; L. Irby, Montana State University, personal communication; S. Stewart, Montana Fish, Wildlife and Parks, personal communication; L. Roop, Wyoming Game and Fish Department, personal communication). The most recent decline was noted in the Madison Range population near Quake Lake, Montana, during the winter of 1996?97. It is believed that disease, predation, and human impacts such as illegal hunting, loss of habitat, and winter recreational use of winter ranges have contributed to these declines. The loss of habitat and the fact that bighorns use traditional migration routes are the primary problems facing bighorn sheep today and are often mentioned as concerns for bighorn sheep management (Constan 1975; Horejsi 1976; Martin 1985; Reisenhoover et al. 1988; Environmental Protection, Fish and Wildlife Service 1993). LIFE HISTORY Adult ewes become mature at 2? years. The breeding season occurs from November through late December, typically on winter range. Lambing occurs from mid-May through June, either near the winter range or during spring migration (May through July), and often along steep, precipitous cliffs. Fall migration is from October through December. The timing of both migrations depends upon weather and snow levels. Bighorn sheep typically remain in separate ewe/lamb and ram groups except during the rut. Males leave ewe/ lamb groups between age 2?3. HABITAT Bighorn sheep utilize different ranges in the winter and summer, and they have an established migration route between these areas. The knowledge of these traditional ranges and migration routes is passed down from one generation to the next. By a bighorn?s fourth year, it has learned its band?s traditional home ranges and migration patterns (Geist 1971, Reisenhoover et al. 1988) and will use them the rest of its life. Any alteration of these habitats or routes could be detrimental for a population of bighorn sheep. The amount of available winter range for Rocky Mountain bighorn sheep is usually more limited than the amount of summer range because of snow depth and spatial distribution. Because of this, winter range can be the critical habitat factor in the survival of bighorn sheep. Bighorns typically use lower elevation ranges in the winter because of low snow coverage in these areas, although some winter at higher elevations on windswept south-southwest facing slopes, usually above the thermocline (Oldemeyer et al. 1971). These higher elevation winter ranges can be problematic because bighorns have limited access to forage. The greater snow depths surrounding the small, available areas of forage habitat make movement from patch to patch difficult. Habitat features that are important for bighorn sheep survival include the distance to escape terrain, slope, salt availability, elevation, aspect, forest cover, shrub availability, biomass and nitrogen content of palatable grasses, and snow depth/snow pack. HUMAN ACTIVITIES Protecting critical winter range by limiting human impacts is important for maintaining bighorn sheep in the GYA. Winter recreational use near or on bighorn sheep winter ranges may affect bighorns during the rut, during winter on the winter ranges that have limited amounts of available habitat, or in the spring during the lambing season. The following types of recreational use could potentially affect bighorn sheep: hikers, wildlife photographers/observers, ice climbers, hunters, snowshoers, skiers, snowmobilers, sled dogs, and dogs on or off leashes. On ranges where bighorns are hunted, they are more sensitive to the presence of humans (Horejsi 1976). Any human activity on bighorn sheep winter range, especially within 100 yards of escape terrain, could affect bighorn sheep survivability. Recreational activities may cause stress in bighorn sheep leading to increased heart rate and energy expenditures (MacArthur et al. 1982) and/or cause displacement from preferred foraging areas to less optimal habitat (Horejsi 1976, Hicks and Elder 1979). Bighorns typically forage during the warmest part of the day to minimize energy loss. If bighorns alter their foraging activities either spatially or temporally, they increase their exposure to predators, decrease the quality and quantity of food available to them, and increase their energy loss. Any decrease in energy intake or increase in energy expenditure as a result of human recreational activity may lead to the death of an already winter-stressed animal either directly by starvation or indirectly by lowering resistance to diseases or predation. The effects of human recreation can be considered an additive factor in lowering survivability in bighorns (Horejsi 1976). MacArthur et al. (1982) showed elevated heart rates and fleeing behavior in bighorn sheep when approached by humans. This behavior was very apparent when humans surprised the bighorns or at any time dogs were present. The heart rate of the bighorns did not decrease with successive approaches, although if a predictable human behavior occurred (i.e., direction and timing of approach), the bighorns became habituated and little response would be noticed except when a dog was present. If bighorns had been harassed earlier by a predator or human, then the current harassment caused a greater response than normal. In Montana, snowmobiles may have contributed to a decline in a bighorn sheep population in the Rock Creek drainage. The stress from the snowmobilers added to the natural stresses incurred during the winter (Berwick 1968). Human disturbance was also found to be a limiting factor for a population of bighorns in the Sierra Nevada Range. Herd size, human distance to the bighorns, and the elevational relationship of humans to bighorns were important factors in determining the reaction of bighorn sheep when approached by humans (Hicks and Elder 1979). Boyle and Samson (1985) noted that rock climbing on or near bighorn sheep escape terrain can affect bighorns. Horejsi (1976) believes that improved access and more leisure time has increased recreational activities (from snowmobiling to walking the dog), which has resulted in more harm to wild bighorns. Because humans behave differently than natural predators (they often persist in following the bighorns to their escape terrain), they can displace bighorns from traditional areas. There is the possibility that bighorn sheep may sometimes congregate near humans as a protection from predators, although the harassment by humans has to be less than the chance of predation. Along the Gallatin Ridge trail, there are two bighorn sheep summer ranges in the Hyalite and Tom Miner basins. There are many areas of bighorn habitat along the 30-mile-long ridge, but bighorn sheep were observed at locations having high visitor use relative to the rest of the area (Legg 1996). In winter, bighorns may not use the human/ predator relationship to select habitat, as winter habitats are already limited to a few select areas. POTENTIAL EFFECTS Recreationists may cause increased stress for bighorn sheep during critical winter months, which may influence their survivability. Human use on the winter range during the breeding season could interfere with breeding by adding more stress to the rams and ewes. This may decrease the overall productivity of the population and increase the probability of predation and death. Bighorns may abandon high quality winter range that is used heavily by humans, or they may limit their use to a small area near escape terrain. These limitations will decrease the available habitat used by bighorns or push them into areas with a greater potential for predation. If bighorns are unable to forage during the day because of recreationists, they will use more energy to forage when it is colder. Development on winter ranges or along migration corridors will decrease the already limited habitat available for bighorns. During the lambing season ewes could be pushed into less optimal habitat, exposing the lambs to predators and environments with harsher weather. Bighorn sheep in the GYA are particularly affected by human use of the following Potential Opportunity Areas: (2) Primary transportation routes (3) Scenic driving routes (6) Backcountry motorized areas (9) Backcountry nonmotorized areas (10) Downhill sliding (nonmotorized) (12) Low-snow recreation areas MANAGEMENT GUIDELINES - Human approach to the critical areas of bighorn habitat should be limited. A buffer zone should be established around bighorn sheep escape terrain. - Human activities should be limited to roads or trails to minimize disturbance to bighorn sheep (MacArthur et al. 1982). - Dogs should be prohibited on any bighorn sheep winter range (MacArthur et al. 1982). - The remaining bighorn sheep habitat should be protected to ensure that migration corridors will remain intact and that traditional ranges are maintained. - Special protection measures should be enforced during brief critical periods such as breeding, lambing, and severe winter weather (Boyle and Samson 1985). - Activities such as ice climbing, wildlife photography/observation, and hiking that occur on lower elevation winter ranges should be monitored very closely. If there is any indication that bighorn sheep are being displaced either spatially or temporally, the activities should be stopped or managed to protect the bighorns. - Skiing, snowmobiling, mountaineering, and snowshoeing will most likely only affect bighorn sheep wintering at higher elevations. The encounters between these recreationists and the bighorns may be infrequent enough that there would be little or no impact to the animals. However, if use increases at these higher elevation winter ranges, managers need to monitor the situation in order to prevent the loss of bighorn sheep on isolated winter ranges. LITERATURE CITED Berwick, S. H. 1968. Observation of the decline of the Rock Creek, Montana, population of bighorn sheep. Thesis, University of Montana, Missoula, Montana, USA. Boyle, S. A., and F. B. Samson. 1985. Effects of nonconsumptive recreation on wildlife: a review. Wildlife Society Bulletin 13:110?116. Buechner, H. K. 1960. The bighorn sheep in the United States; its past, present, and future. Wildlife Monographs Number 4. Caslick, J. W. 1993. Bighorn sheep in Yellowstone: a literature review and some suggestions for management. National Park Service, Yellowstone National Park, Wyoming, USA. Constan, K. J. 1975. Fish and Game Planning, Upper Yellowstone and Shields River drainages. Montana Department of Fish and Game, Environment and Information Division Federal Aid to Fish and Wildlife Restoration Project FW-3-R:128?183. Helena, Montana, USA. Environmental Protection, Fish and Wildlife Service. 1993. Management plan for bighorn sheep in Alberta. Wildlife Management Planning Series Number 6. Edmonton, Alberta, Canada. Geist, V. 1971. Mountain sheep, a study in behavior and evolution. University of Chicago Press, Chicago, Illinois, USA. Hicks, L. L., and J. M. Elder. 1979. Human disturbance of Sierra Nevada bighorn sheep. Journal of Wildlife Management 43(4):909?915. Horejsi, B. 1976. Some thoughts and observations on harassment of bighorn sheep. Pages 149?155 in T. Thorne, chairman. Proceedings of the Biennial Symposium of North American Bighorn Sheep Council. Jackson, Wyoming, USA. Jones, L. C. 1994. Evaluation of lungworm, nutrition, and predation as factors limiting the recovery of the Stillwater bighorn sheep herd. Thesis, Montana State University, Bozeman, Montana, USA. Keating, K. A. 1982. Population ecology of Rocky Mountain bighorn sheep in the upper Yellowstone River drainage, Montana/ Wyoming. Thesis, Montana State University, Bozeman, Montana, USA. Legg, K. L. 1996. Movements and habitat use of bighorn sheep along the upper Yellowstone River Valley, Montana. Thesis, Montana State University, Bozeman, Montana, USA. Lemke, T. 1996. Annual report. Montana Fish, Wildlife and Parks, Helena, Montana, USA. MacArthur, R. A., V. Geist, and R. H. Johnson. 1982. Cardiac and behavioral responses of mountain sheep to human disturbance. Journal of Wildlife Management 46:351?358. Martin, S. 1985. Ecology of the Rock Creek bighorn sheep herd, Beartooth Mountains, Montana. Thesis, Montana State University, Bozeman, Montana, USA. Meagher, M., W. J. Quinn, and L. Stackhouse. 1992. Chlamydial-caused infectious keratoconjunctivitis in bighorn sheep of Yellowstone National Park. Journal of Wildlife Disease 28(2):171?176. Mills, H. B. 1937. A preliminary study of the bighorn of Yellowstone National Park. Journal of Mammalogy 18:205?212. Oldemeyer, J. L., W. J. Barmore, and D. L. Gilbert. 1971. Winter ecology of bighorn sheep in Yellowstone National Park. Journal of Wildlife Management 35:257?269. Reisenhoover, K. L., J. A. Bailey, and L. A. Wakelyn. 1988. ?In my opinion,? assessing the Rocky Mountain bighorn sheep management problem. Wildlife Society Bulletin 16(3):346?352. Seton, E. T. 1913. Wild animals at home. Doubleday, Page & Company, Garden City, New York, USA. PREPARED BY: Kristin Legg, Wildlife Biologist, National Park Service, Pipestone National Monument, Pipestone, Minnesota, USA. (Formerly at Yellowstone National Park.) PRESENTED AT: Northern Bighorn Sheep and Mountain Goat Biennial Symposium, April 1996, Whitefish, Montana, USA.

Keywords: animal, mammal, ungulate, sheep, bighorn sheep, Ovis canadensis, population, mortality, human activity, wildlife, management, bibliography, livestock, disease, hunting, habitat, food, forage, Greater Yellowstone Ecosystem, Yellowstone National Park, predation, poaching, migration, breeding, distribution