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WILDLIFE SPECIES:  Ovis canadensis


WILDLIFE SPECIES: Ovis canadensis
AUTHORSHIP AND CITATION : Tesky, Julie L. 1993. Ovis canadensis. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: [].
ABBREVIATION : OVCA COMMON NAMES : bighorn sheep mountain sheep TAXONOMY : The currently accepted scientific name for the bighorn sheep is Ovis canadensis Shaw [6,13]. Subspecies are listed below [13]. Ovis canadensis subsp. canadensis (Rocky mountain bighorn sheep) Ovis canadensis subsp. auduboni Merriam (Audubon's bighorn sheep) Ovis canadensis subsp. californiana Douglas (California bighorn sheep) Ovis canadensis subsp. cremnobates Elliot (Peninsular desert bighorn sheep) Ovis canadensis subsp. mexicana Merriam (Mexican desert bighorn sheep) Ovis canadensis subsp. nelsoni Merriam (Nelson's Peninsular bighorn sheep) Ovis canadensis subsp. sierrae (Sierra Nevada bighorn sheep) Ovis canadensis subsp. weemsi Goldman (Weem's desert bighorn sheep) ORDER : Artiodactyla CLASS : Mammal FEDERAL LEGAL STATUS : Nelson's Peninsular and Sierra Nevada bighorn sheep are listed as Endangered [28]. OTHER STATUS : Information on state- and province-level protection status of animals in the United States and Canada is available at NatureServe, although recent changes in status may not be included.


WILDLIFE SPECIES: Ovis canadensis
GENERAL DISTRIBUTION : The former range of the bighorn sheep extended from the Northern Rocky Mountains of Canada south to the mainland of Mexico and Baja California [22]. It is now found in relatively isolated pockets in the Coast and Cascade ranges and the Sierra Nevada, and in the Rocky Mountains south of the Peace River to Mexico [6]. ECOSYSTEMS : FRES20 Douglas-fir FRES21 Ponderosa pine FRES23 Fir-spruce FRES26 Lodgepole pine FRES29 Sagebrush FRES30 Desert shrub FRES32 Texas savanna FRES33 Southwestern shrubsteppe FRES34 Chaparral-mountain shrub FRES35 Pinyon-juniper FRES36 Mountain grasslands FRES37 Mountain meadows FRES38 Plains grasslands FRES39 Prairie FRES40 Desert grasslands FRES44 Alpine STATES :
BLM PHYSIOGRAPHIC REGIONS : 1 Northern Pacific Border 2 Cascade Mountains 3 Southern Pacific Border 4 Sierra Mountains 5 Columbia Plateau 6 Upper Basin and Range 7 Lower Basin and Range 8 Northern Rocky Mountains 9 Middle Rocky Mountains 10 Wyoming Basin 11 Southern Rocky Mountains 12 Colorado Plateau 13 Rocky Mountain Piedmont 16 Upper Missouri Basin and Broken Lands KUCHLER PLANT ASSOCIATIONS : K003 Silver fir - Douglas-fir forest K004 Fir - hemlock forest K005 Mixed conifer forest K010 Ponderosa shrub forest K011 Western pondersoa forest K012 Douglas-fir forest K015 Western spruce - fir forest K016 Eastern ponderosa forest K018 Pine - Douglas-fir forest K019 Arizona pine forest K020 Spruce - fir - Douglas-fir forest K021 Southwestern spruce - fir forest K022 Great Basin pine forest K024 Juniper steppe woodland K023 Juniper - pinyon woodland K028 Mosaic of K002 and K026 K029 California mixed evergreen forest K031 Oak - juniper woodlands K032 Transition between K031 and K037 K035 Coastal sagebrush K037 Mountain-mahogany - oak scrub K038 Great Basin sagebrush K039 Blackbrush K040 Saltbush - greasewood K041 Creosotebush K042 Creosotebush - bursage K047 Fescue - oatgrass K050 Fescue - wheatgrass K051 Wheatgrass - bluegrass K053 Grama - galleta steppe K054 Grama - tobosa prairie K057 Galleta - three-awn shrubsteppe K058 Grama - tobosa shrubsteppe K059 Trans-Pecos shrub savanna K052 Alpine meadows and barren K063 Foothills prairie K064 Grama - needlegrass - wheatgrass K065 Grama - buffalograss K066 Wheatgrass - needlegrass K067 Wheatgrass - bluestem - needlegrass K068 Wheatgrass - grama - buffalograss K069 Bluestem - grama prairie K070 Sandsage - bluestem prairie K074 Bluestem prairie SAF COVER TYPES : 204 Black spruce 205 Mountain hemlock 206 Engelmann spruce - subalpine fir 208 Whitebark pine 210 Interior Douglas-fir 218 Lodgepole pine 220 Rocky Mountain juniper 230 Douglas-fir - western hemlock 237 Interior ponderosa pine 238 Western juniper 239 Pinyon - juniper SRM (RANGELAND) COVER TYPES : NO-ENTRY PLANT COMMUNITIES : Bighorn sheep occupy a variety of plant communities ranging from alpine meadows, woodlands, mixed-grass prairie, shrub-bunchgrass, and dry pinyon-juniper (Pinus-Juniperus spp.) [2,7,14,25,27]. They avoid dense forests [6]. Summer ranges of bighorn sheep in southeastern Oregon vary from subalpine meadows or grasslands to sagebrush (Artemisia spp.)/grasslands or shrublands. Winter ranges are usually shrub/grasslands and shrublands. Communities dominated by trees or tall shrubs such as aspen (Populus spp.), cottonwood (Populus spp.), fir (Abies spp.), pine, juniper, mountain-mahogany (Cercocarpus spp.), squaw apple (Peraphyllum ramosissimum), and cherry (Prunus spp.) may occur throughout both summer and winter ranges [26]. On two bighorn sheep winter ranges in the upper Yellowstone River Valley, vegetation types in which bighorns were observed included bluebunch wheatgrass (Pseudoroegneria spicata), needle-and-thread (Stipa comata), and Idaho fescue (Festuca idahoensis) grasslands; sagebrush (primarily A. tridentata) and black greasewood (Sarcobatus vermiculatus) shrublands; open Douglas-fir (Pseudotsuga menziesii) woodland; and the vegetation mosaics associated with cliffs and draws [14]. Bighorn sheep range in Glacier National Park includes bunchgrass communities dominated by bluebunch wheatgrass, Idaho fescue, rough fescue (F. scrabrella), and Saskatoon serviceberry (Amelanchier alnifolia); and seral vegetation of subalpine fir (Abies lasiocarpa) habitat types [24]. Other plant species common on bighorn sheep range include bitterbrush (Purshia tridentata), mountain muhly (Muhlenbergia montana), russet buffaloberry (Shepherdia canadensis), bearberry (Arctostaphylos uva-ursi), blue grama (Bouteloua gracilis), rabbitbrush (Chrysothamnus spp.), bluegrass (Poa spp.), buffalograss (Buchloe dactyloides), western wheatgrass (Pascopyron smithii), and sedges (Carex spp.) [2,7,11,24,25].


WILDLIFE SPECIES: Ovis canadensis
TIMING OF MAJOR LIFE HISTORY EVENTS : Breeding season - Bighorn sheep are polygamous. Ewes are monesterous. Rams of most subspecies rut in November and December. However, desert bighorn sheep may rut for up to 9 months, with rutting reaching a peak in August and September [6]. Age at sexual maturity - The age at which ewes attain sexual maturity is quite variable and is dependent mainly on their physical condition [6]. Most bighorn sheep become mature at 2.5 years of age. Large-bodied rams may reach sexual maturity within 18 months, but smaller rams may take as long as 36 months. Very old ewes generally do not breed [6]. Gestation and lambing - The gestation period is 5.5 to 6 months. The majority of ewes give birth to one lamb per year. Lambing of northern bighorn sheep occurs between late April and late June, with most lambs born before the end of May. Desert bighorn sheep ewes give birth throughout the year; however, the peak is from January to April [6]. Development of lambs - Bighorn sheep lambs are precocious and within a day or so climb almost as well as their mothers. Within 2 weeks lambs can eat grass. They are weaned between 1 and 7 months. By their second spring bighorn sheep are totally independent of their mother. Ewes reach their adult weight by 4 to 5 years of age, while rams do not achieve maximum weight until they are 6 or 7 years old [6]. Life span - Mortality is high for bighorn sheep 1 to 2 years of age, drops to a relatively low rate for 2 to 8 years of age, then increases to a maximum for those older than 8 to 9 years. Bighorn sheep that live past 8 or 9 years may live to 15 to 17 years of age, but 10 to 12 years is more common [6]. Bighorn sheep are territorial. By 4 years of age, individuals have established home ranges that are utilized throughout their life span [6]. PREFERRED HABITAT : Bighorn sheep inhabit remote mountain and desert regions. They are restricted to semiopen, precipitous terrain with rocky slopes, ridges, and cliffs or rugged canyons [6,26]. Forage, water, and escape terrain are the most important components of bighorn sheep habitat [26]. Winter range - Generally, bighorn sheep have two distinct, separate summer and winter ranges [6]. Most of the year is spent on the winter range, where the elevation is typically below 10,826 feet (3,300 m). The aspect is usually south or southwest. Rams often venture onto the more open slopes, although rugged terrain is always nearby. Desert bighorn sheep rarely stray far from the base of a mountain and usually are found on eastern aspects, where they use dry gullies. During severe weather, if snow becomes unusually deep or crusted, bighorn sheep move to slightly higher elevations where wind and sunshine have cleared the more exposed slopes and ridges [6]. Spring range - The spring range is generally characterized by the same parameters as the winter range. However, bighorn sheep begin to respond to local greenups along streambanks and valleys. Bighorn sheep use areas around saltlicks heavily in the spring. Preferred lambing range is in the most precipitous, inaccessible cliffs near forage, and generally has a dry, southern exposure [6]. Summer range - In the summer, bighorn sheep are mostly found grazing on grassland meadows and plateaus above timber. In early summer south and southwestern exposures are most frequently utilized; however, in the case of the desert bighorn sheep the eastern aspect is preferred. By late summer the more northerly exposures are preferred [6]. Snow accumulation seems to be the principal factor that triggers bighorn sheep to move from summer to winter ranges [26]. Water - Bighorn sheep obtain water from dew, streams, lakes, springs, ponds, catchment tanks, troughs, guzzlers, and developed seeps or springs [26]. Alkaline water is not suitable. Bighorn sheep spend most of their time within 1 mile (1.6 km) of water but have been located as far as 2 miles (3.2 km) from water. Water sources more than 0.3 mile (0.5 km) from escape terrain or surrounded by tall dense vegetation are avoided by bighorn sheep [26]. Desert bighorn sheep primarily utilize ephemeral water sources. They may drink every day if water is nearby, but may go without water for up to 14 days in the dry season. Since water is one of the major limiting factors of desert bighorn sheep, management agencies have installed cisterns and other water developments in critical areas [6]. COVER REQUIREMENTS : Escape terrain is an important habitat requirement for bighorn sheep. Cliffs, rock rims, rock outcroppings, and bluffs with sparse cover of trees or shrubs typify escape habitat, which provides both thermal and hiding cover. While bighorn sheep are not always found in precipitous mountain areas, ewes and lambs rely on these areas for escape cover, especially during the lambing period [6,26,27]. Visibility is another important habitat component for bighorn sheep. It allows for predator detection, visual communication, and efficient foraging [4]. Bighorn sheep tend to forage in open areas with low vegetation such as grasslands, shrublands, or mixes of these. They avoid foraging on mild slopes with shrub or canopy cover in excess of 25 percent and shrubs 2 feet (60 cm) or higher. On steep slopes they have been noted to travel through or bed in dense brush [26]. FOOD HABITS : Bighorn sheep primarily graze grasses and forbs, but eat other vegetation depending on availability [6]. They prefer green forage and move up- or downslope or to different aspects for more palatable forage. Forage areas that provide a variety of aspects are preferable because they provide green forage for longer periods [26]. Bighorn sheep eat sedges and a variety of grasses including bluegrasses (Poa spp.), wheatgrasses, bromes, and fescues. Browse species include sagebrush, willow (Salix spp.), rabbitbrush, curlleaf mountain-mahogany (Cercocarpus ledifolius), winterfat (Kraschnennikovia lanata), bitterbrush, and green ephedra (Ephedra spp.). Forbs include phlox (Phlox spp.), cinquefoil (Potentilla spp.), twinflower (Linnaea borealis), and clover (Trifolium spp.) [6,23]. Because of the dry climate, browse is the dominant food of the desert bighorn sheep and includes desert holly (Atriplex hymenelytra), honeysweet (Tidestromia oblongifolia), brittlebush or encelia (Encelia spp.), hairy mountain-mahogany (C. breviforus), Wright silktassel (Garrya wrightii), desert mallow (Sphaeralcea ambigua), Russian-thistle (Salsola kali), false mesquite (Calliandra eriophylla), goatnut (Simmondsia chinensis), white ratany (Krameria canescens), bursage (Hyptis emoryi), mesquite (Prosopis glandulosa), catclaw (Acacia greggii), ironwood (Olneya tesota), paloverde (Cercidium spp.), pincushion (Mammillaria spp.), and saguaro (Carnegiea gigantea). Dry grasses are eaten throughout the year and are an important food reserve, especially near waterholes [6]. PREDATORS : Golden eagles (Aquila chrysaetos) occasionally threaten bighorn sheep lambs, but are rarely successful in taking one. Bighorn sheep are an incidental food item in the diet of grizzly or black bears (Ursus arctos, U. americanus) and wolverines (Gulo gulo), and are generally eaten only as carrion. Wolves (Canis lupus), coyotes (C. latrans), mountain lions (Felis concolor), and bobcats (Lynx rufus) are other predators of bighorn sheep [6,26]. The number of bighorn sheep taken by predators is usually of little consequence to healthy populations. Predators are most effective when locations of escape terrain or water limit sheep movement and allow predators to concentrate hunting efforts [26]. Bighorn sheep are hunted by humans. Hunting has traditionally been for rams only and is further restricted by a 3/4 or full horn curl policy. In the last few years most states and provinces have adopted more stringent horn curl regulations. While the overall trend has been for more restrictive hunting seasons, in some cases local situations have dictated either sex or 1/2 curl ram seasons [6]. MANAGEMENT CONSIDERATIONS : Bighorn sheep are very susceptible to diseases. Incidence of lungworm infestation approaches 100 percent in some herds, although the level of individual infection varies depending upon sheep and domestic livestock densities, range conditions, climate, season, and age. Desert bighorn sheep appear to have lighter infestations, possibly due to climate or low density. A significant correlation exists between the intensity of the lungworm infestation and the amount of precipitation in the spring of the previous year. In Washington state both wild and captive bighorn sheep have been successfully treated with the experimental drug albendazole. Further research is needed to determine the feasibility of treating remote populations [6]. The future of bighorn sheep depends on the preservation and improvement of critical native ranges. Bighorn sheep are poor competitors with other wild and domestic ungulates, and their range is diminishing. The effect of domestic livestock grazing on bighorn sheep is controversial and depends on the proximity and population size of competing species. Domestic livestock have been reported to have little deleterious effect if they do not graze on critical bighorn sheep winter ranges. Nevertheless, extensive competition by livestock, especially on public lands, persists and is one of the reasons for the decline in density of bighorn sheep populations [6]. Elk (Cervus elaphus) and deer (Odocoileus virginianus and O. hemionus) can also be serious competitors with bighorn sheep on marginal habitat [6,18]. Human activities on bighorn sheep range are the most widespread threat to bighorn sheep [4]. These activies reduce the number of bighorn sheep by decreasing habitat, causing bighorn sheep to reduce or terminate their use of prime habitat, stop migration, or split from large herds into smaller herds [4,26]. Human activities responsible for declines in sheep use of an area include hiking and backpacking, snow skiing, water skiing, fishing, motorbiking, four-wheel-drive vehicle use, construction and use of roads, urban development, and recreational development. When bighorn sheep are pushed from prime to marginal habitat, mortality usually increases and productivity decreases. Some herds have adapted to human activity [26].


WILDLIFE SPECIES: Ovis canadensis
DIRECT FIRE EFFECTS ON ANIMALS : Prescribed burning and its associated human activity in bighorn sheep range may increase stress levels in a population. Herd condition should be considered when planning time of fire [27]. No information is available regarding the direct effects of fire on bighorn sheep. HABITAT RELATED FIRE EFFECTS : Many bighorn sheep populations originally occurred in areas with frequent fire intervals [19,24]. Bighorn sheep inhabiting the Salmon River drainage of Idaho occupy a region where over 64 percent of their habitat has burned since 1900 [24]. Fire exclusion for over 50 years has allowed plant succession to alter many bighorn sheep habitats throughout North America [6,7]. Fire exclusion, which has allowed conifers to establish on grasslands, has decreased both the forage and security values on many bighorn sheep ranges [7]. Fire is an important factor in creating habitats that are heavily used by bighorn sheep [6,27]. Periodic burning keeps seral grasslands from becoming dominated by coniferous trees [27]. In April 1987, a prescribed fire was conducted on 235 acres (95 ha) of bighorn sheep winter range in Custer State Park, South Dakota. Burning expanded foraging habitat for bighorn sheep by curtailing encroachment of pondersosa pine (Pinus ponderosa) onto mixed-grass prairie. Burning may regenerate rangelands and enhance the production, availability, and palatability of important bighorn sheep forage species [27]. Bighorn sheep heavily utilized burned winter range the following two winters after a September 1974 fire on the East Fork of the Salmon River, Idaho [19]. Over 66 percent of the plants on this burned range had been grazed by bighorn sheep. Utilization was consistently higher on burned sites than on adjacent unburned sites for at least 4 years after the fire [19]. Burning can increase visibility for bighorn sheep. Research has shown that on burned sites bighorn sheep use areas more distant to escape terrain than on adjacent unburned sites [27]. Fire can negatively affect bighorn sheep habitat when range condition is poor and forage species cannot recover, when nonsprouting species that provide important forage for bighorn sheep are eliminated, or when too much area is burned and forage is inadequate until the next growing season. Another potentially negative effect is when other species, especially elk, are attracted to prescribed burns intended to benefit bighorn sheep [19]. FIRE USE : Prescribed fire can be useful tool in managing bighorn sheep habitat [19]. Prescribed burning has been widely used to increase the quantity and nutritional quality of bighorn sheep forage throughout North America [7]. Prescribed crown fires conducted in winter in mature conifer stands adjacent to escape terrain may provide an inexpensive solution to maintaining or establishing bighorn sheep winter range. In areas where the available bighorn sheep range is large and provides alternative and distant wintering sites, fires should be prescribed or located in areas that would minimize the stress on sheep. Early spring fires, particularly on south and southwest aspects, may provide more spring forage than would otherwise be available for bighorn sheep [27]. Burning immature forests and scrublands adjacent to bighorn sheep winter range could also provide migration corridors between winter and summer ranges [24]. Prescribed burning has been used to establish and maintain subalpine bighorn sheep range in British Columbia. According to Bentz and Woodard [2], burning provides an economical method of converting subalpine forests, which are of low value to bighorn sheep, to earlier seral plant communities. On the British Columbia range, bighorn sheep used burned sites more than adjacent unburned sites. Since both positive and negative effects can occur from burning bighorn sheep range, a well-thought-out plan must be developed before fire is considered for use on their range. Plans must consider the following: 1) condition of plants 2) plant response to burning 3) adjacent conifers (The possibility of creating more open range exists if conifer stands or tall shrub fields occur next to currently used ranges.) 4) limiting factors (factors that may limit bighorn sheep populations should be identified, and an evaluation made as to how burning will effect these limiting factors) 5) lungworm (lungworm infections can possibly be altered by reducing bighorn sheep concentrations; however, if burns are small and concentrate bighorn sheep, results could be negative. If burns disperse populations, the effects could be positive) 6) competition from other ungulates attracted to burns [19] FIRE REGIMES : Find fire regime information for the plant communities in which this species may occur by entering the species name in the FEIS home page under "Find Fire Regimes".


WILDLIFE SPECIES: Ovis canadensis
REFERENCES : 1. Bailey, James A. 1990. Management of Rocky Mountain bighorn sheep herds in Colorado. Special Report No. 66. Denver, CO: Colorado Department of Natural Resources, Division of Wildlife, Terrestrial Wildlife Research. 24 p. [19255] 2. Bentz, Jerry A.; Woodard, Paul M. 1988. Vegetation characteristics and bighorn sheep use on burned and unburned areas in Alberta. Wildlife Society Bulletin. 16(2): 186-193. [15276] 3. Bernard, Stephen R.; Brown, Kenneth F. 1977. Distribution of mammals, reptiles, and amphibians by BLM physiographic regions and A.W. Kuchler's associations for the eleven western states. Tech. Note 301. Denver, CO: U.S. Department of the Interior, Bureau of Land Management. 169 p. [434] 4. Boyd, Raymond J.; Cooperrider, Allen Y.; Lent, Peter C.; Bailey, James A. 1986. Ungulates. In: Cooperrider, Allen Y.; Boyd, Raymond J.; Stuart, Hanson R., eds. Inventory and monitoring of wildlife habitat. Denver, CO: U.S. Department of the Interior, Bureau of Land Management, Service Center: 519-564. [10856] 5. Butts, Thomas W. 1977. Preliminary investigations of the bighorn sheep of upper Rock Creek, Granite County, Montana. Report. Boulder, CO: Western Interstate Commission for Higher Education. 41 p. [19358] 6. Chapman, Joseph A.; Feldhamer, George A., eds. 1982. Wild mammals of North America. Baltimore, MD: The Johns Hopkins University Press. 1147 p. [21085] 7. Easterly, Thomas G.; Jenkins, Kurt J. 1991. Forage production and use on bighorn sheep winter range following spring burning in grassland and ponderosa pine habitats. Prairie Naturalist. 23(4): 193-200. [19277] 8. Ecology USA. 1992. Recent actions under the Endangered Species Act. Ecology. 21(10): 97-98. [18849] 9. Eyre, F. H., ed. 1980. Forest cover types of the United States and Canada. Washington, DC: Society of American Foresters. 148 p. [905] 10. Garrison, George A.; Bjugstad, Ardell J.; Duncan, Don A.; [and others]. 1977. Vegetation and environmental features of forest and range ecosystems. Agric. Handb. 475. Washington, DC: U.S. Department of Agriculture, Forest Service. 68 p. [998] 11. Goodson, Nike J.; Stevens, David R.; Bailey, James A. 1991. Winter-spring foraging ecology and nutrition of bighorn sheep on montane ranges. Journal of Wildlife Management. 55(3): 422-433. [15425] 12. Hailey, Tommy L. 1974. Past, present, and future status of the desert bighorn in the Chihuahuan Desert bighorn in the Chihuahuan Desert region. In: Wauer, Roland H.; Riskind, David H., eds. Transactions of the symposium on the biological resources of the Chihuahuan Desert region, United States and Mexico; 1974 October 17-18; Alpine, TX. Transactions and Proceedings Series No. 3. Washington, DC: U.S. Department of the Interior, National Park Service: 217-220. [16060] 13. Hall, E. Raymond; Kelson, Keith R. 1959. The mammals of North America, Volume II. New York: The Ronald Press Company. 79 p. [21460] 14. Keating, Kimberly A.; Irby, Lynn R.; Kasworm, Wayne F. 1985. Mountain sheep winter food habits in the upper Yellowstone Valley. Journal of Wildlife Management. 49(1): 156-161. [15521] 15. Kuchler, A. W. 1964. Manual to accompany the map of potential vegetation of the conterminous United States. Special Publication No. 36. New York: American Geographical Society. 77 p. [1384] 16. Miller, Gary D.; Gaud, William S. 1989. Composition and variability of desert bighorn sheep diets. Journal of Wildlife Management. 53(3): 597-606. [14429] 17. Moseley, Robert; Groves, Craig, compilers. 1990. Rare, threatened and endangered plants and animals of Idaho. Boise, ID: Idaho Department of Fish and Game, Nongame and Endangered Wildlife Program, Natural Heritage Section. 33 p. [19328] 18. Peek, James. 1985. Bighorn sheep responses to fire. The Habitat Express. No. 85-4. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Region. 3 p. [5224] 19. Peek, James, M.; Demarchi, Dennis A.; Demarchi, Raymond A.; [and others]. 1985. Bighorn sheep and fire: seven case histories. In: Lotan, James E.; Brown, James K., compilers. Fire's effect on wildlife habitat--symposium proceedings; 1984 March 21; Missoula, MT. Gen. Tech. Rep. INT-186. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station: 36-43. [1864] 20. Peek, James M.; Riggs, Robert A.; Lauer, Jerry L. 1979. Evaluation of fall burning on bighorn sheep winter range. Journal of Range Management. 32(6): 430-432. [1863] 21. Ramirez, Bernardo Villa. 1974. Major game mammals and their habitats in the Chihuahuan Desert region. In: Wauer, Roland H.; Riskind, David H., eds. Transactions of the symposium on the biological resources of the Chihuahuan Desert region, United States and Mexico; 1974 October 17-18; Alpine, TX. Transactions and Proceedings Series No. 3. Washington, DC: U.S. Department of the Interior, National Park Service: 155-161. [16059] 22. Reel, Susan; Schassberger, Lisa; Ruediger, William, compilers. 1989. Caring for our national community: Region 1 - threatened, endangered & sensitive species program. Missoula, MT: U.S. Department of Agriculture, Forest Service, Northern Region. 309 p. [19675] 23. Stelfox, John G. 1976. Range ecology of Rocky Mountain bighorn sheep in Canadian national parks. Report Series Number 39. Ottawa, ON: Canadian Wildlife Service. 50 p. [13851] 24. Stucker, Donald E.; Peek, James M. 1984. Response of bighorn sheep to the Ship Island Burn. Report submitted to the Northern Forest Fire Laboratory: Supplement No. INT-80-108CA. 33 p. On file at: U.S. Department of Agriculture, Forest Service, Intermountain Research Station, Fire Sciences Laboratory, Missoula, MT. [17070] 25. Todd, J. W. 1975. Foods of Rocky Mountain bighorn sheep in southern Colorado. Journal of Wildlife Management. 39(1): 108-111. [6218] 26. Van Dyke, Walter A.; Sands, Alan; Yoakum, Jim; [and others]. 1983. Wildlife habitats in managed rangelands--the Great Basin of southeastern Oregon: bighorn sheep. Gen. Tech. Rep. PNW-159. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest and Range Experiment Station. 37 p. [2417] 27. Woodard, Paul M.; Van Nest, Terry. 1990. Winter burning bighorn sheep range--a proposed strategy. Forestry Chronicle. October: 473-477. [14619] 28. U.S. Department of the Interior, Fish and Wildlife Service. 2016. Endangered Species Program, [Online]. Available: [86564]

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