Desert Bighorn Sheep

Desert Bighorn Sheep
		by *Henry E. McCutchen* National Biological Service
Desert bighorn sheep (Ovis canadensis spp.) are subspecies of concern in the continental United States. Populations declined drastically with European colonization of the American Southwest beginning in the 1500's (Buechner 1960). At present, desert bighorn numbers are extremely low, although the overall population trend has increased since 1960.
Desert bighorn are considered good indicators of land health because the species is sensitive to many human-induced environmental problems (McCutchen 1981). In addition to their aesthetic value, desert bighorn are considered desirable animals by hunters.
The Rocky Mountain and California races of bighorn occupy the cooler western and northwestern regions of the United States. In contrast, the desert sheep races are indigenous to the hot desert ecosystems of the Southwest.
Population Trends
The number of desert bighorn in North America in pristine times is unknown but most likely was in the tens of thousands (Buechner 1960). Seton (1929) estimated the pre-Columbian numbers of all subspecies of bighorn in North America (United States, Canada, and Mexico) at 1.5-2 million. By 1960, however, the overall bighorn population in the United States, including desert bighorns, had dwindled to 15,000-18,200 (Buechner 1960). Buechner documented major declines from the 1850's to the early 1900's. These declines were attributed to excessive hunting; competition and diseases from domestic livestock, particularly domestic sheep; usurpation of watering areas and critical range by human activities; and human-induced habitat changes (Buechner 1960; Graham 1980; McCutchen 1981).

These declines were followed by a period of population stabilization that Buechner ascribed to conservation measures. The decline of desert bighorn probably mirrored the pattern of decline of the overall bighorn population. Desert bighorn population trends have been upward since the 1960's when Buechner (1960) estimated their population at 6,700-8,100. In 1980 desert bighorn populations were estimated at 8,415-9,040 (Wishart 1978). Weaver (1985) conducted a state-by-state survey a few years later and estimated the U.S. desert bighorn population at 15,980. The 1993 estimate of the population is 18,965-19,040 (Table).

Table. Status and trends of desert bighorn sheep in the United States 1960-93. Estimate for 1960 by Buechner (1960). Estimates for 1993 from state wildlife agency status reports presented to the Desert Bighorn Council, Moab, Utah, 1994.

	Population estimate by year
State	1960	1993
Arizona	3,000-3,500	6,000
California	2,140-2,450	4,300-4,325^*
Colorado	0	475
Nevada	1,500-2,000	5,294
New Mexico	400-500	295
Texas	25	401
Utah	Remnant	2,200-2,250
Total	7,065-8,475	18,965-19,040

^In California, Nelson's bighorn (Ovis canadensis nelsoni) population trends are upward. Peninsular bighorn (O.c. cremnobates*) populations are lower and are of concern.

Subspecies
Cowan (1940) used morphological characters and measurements to identify three subspecies of desert bighorns (O.c. nelsoni, O.c. mexicana, and O.c. cremnobates) occurring in the United States. A recent reevaluation of mountain sheep races in the United States, however, suggested significant differences between the northern and southern (desert) sheep (Ramey 1993). Differences among the three desert bighorn races, however, did not support separate subspecies designations.

Figure. Historical range and current distribution of the three subspecies of desert bighorn in the United States (redrawn from Trefethen 1975 and Weaver 1985).
The distribution of desert bighorn races is uncertain, although the distribution maps of Trefethen (1975) and Weaver (1985) are accepted by mountain sheep biologists (Figure).

Status and Trends by State
Arizona
Historically, desert bighorn occurred on all mountain ranges and plateau slopes in the southern, northern, and western sections of Arizona (Russo 1956). In spite of early protection (beginning in the 1880's), researchers believed that bighorn populations declined until the 1950's (Russo 1956).
Arizona began a limited hunting program in 1953 and reintroduction programs in 1958. The Arizona Game and Fish Department conducts annual helicopter surveys. Buechner (1960) estimated the 1960 population at about 3,000-3,500. In 1993 the population had increased to an estimated 6,000 (R. Lee, Arizona Game and Fish Department, unpublished data).
California

Desert bighorn sheep (Ovis canadensis nelsoni). Courtesy H.E. McCutchen

Desert bighorn occupied desert mountains in southeast California in historical times. California protected bighorn in 1883, and by 1960 Buechner (1960) estimated the population at about 2,150-2,450 (1,800-2,100 O.c. nelsoni and 350 O.c. cremnobates). The state began transplanting in 1971 and permitted hunting beginning in 1986 (Bleich et al. 1990). In 1993 the populations were estimated at 4,300-4,325, with the breeds occupying about 50 mountain ranges (S. Torres, California Department of Fish and Game, unpublished data).

The less common peninsular bighorn (O.c. cremnobates) occurs in the desert mountains of southeast California from Palm Springs south to the Mexican border. From 1977 to 1993 this population declined from an estimated 1,171 to 400-425 individuals because of excessive lamb mortality (Weaver 1989; S. Torres, California Department of Fish and Game, unpublished data). In 1992 the U.S. Fish and Wildlife Service proposed listing the peninsular bighorn as endangered (Torres et al. 1993). This subspecies also occurs southward into Mexico; populations there are larger. One survey estimated a population of 780-1,170 adult bighorn in northern Baja California, Mexico (DeForge et al. 1993).
Colorado
There is no scientific evidence that desert bighorn occurred historically in Colorado, although there is habitat in the state contiguous with desert bighorn habitat in Utah. Thus, desert bighorn probably occurred in the state, and became extirpated before subspecies' determinations could be made.
The Colorado Division of Wildlife began transplanting desert bighorn in 1979. By 1993 populations containing approximately 475 bighorn had been established from the release of animals originally from Arizona and Nevada (Wolfe 1990; V. Graham, Colorado Division of Wildlife, unpublished data).
Nevada
Desert bighorn (O.c. nelsoni) historically occupied the central and southern portions of Nevada (McQuivey 1978). Hunting the animals was prohibited from 1901 to 1952. Transplanting programs have been successful: between 1968 and 1988 more than 800 desert bighorn were transplanted. From these animals, 21 transplanted herds have been established (Delaney 1989).
Buechner (1960) estimated the Nevada population at 1,500-2,000 in 1960. The state began annual population trend counts in 1969. In 1993 the population was estimated at 5,294 animals, occupying 45 mountain ranges (P. Cummings, Nevada Division of Wildlife, unpublished data).
New Mexico
Although desert bighorns (O.c. mexicana) historically occupied mountain ranges and canyons in the southern part of New Mexico, by 1930 the animals were restricted to only four mountain ranges, and by the late 1940's were found in only two (Weaver 1985).
In 1972 the state constructed the 300-ha (741 acres) Red Rock propagating enclosure and added brood stock. Transplants from the captive herd were subsequently made into the Big Hatchet, Peloncillo, and Alamo Hueco mountains (Sandoval 1979).
The San Andres Mountain population was formerly the state's largest, but declined from 200 to fewer than 25 by 1991 (Clark and Jessup 1992) because of psoroptic scabies (Psoroptes spp.).
Buechner estimated the New Mexican population at 400-500 in 1960. In 1993 the estimated population was 295, of which 100 were at Red Rock (A. Fisher, New Mexico Department of Game and Fish, unpublished data).
Texas
Desert bighorn (O.c. mexicana) appear to have occupied all the mountains in southwest Texas west of the Pecos River (Carson 1941). In 1880 the population was estimated at 1,500 animals (Kilpatric 1982); some populations still existed in the late 1930's. By the mid-1950's all bighorns had become extirpated except for a small herd of 25; excessive hunting and competition with domestic livestock are believed to have been major factors in the final decline (Buechner 1960).
In 1957 the Texas Game and Fish Department began a highly successful captive breeding and release program. By 1993 the free-ranging population was estimated at 310; 91 other sheep were in captivity (G. Calkins, Texas Parks and Wildlife Department, unpublished data).
Utah
Historically, desert bighorn (O.c. nelsoni) occupied canyons and ranges in southern and eastern Utah. Significant population declines occurred in the 1870's (Buechner 1960), and the state did not permit hunting of bighorn from 1899 to 1967.
In 1967 limited hunting began, and in 1973 the state started an active transplant program. Between 1973 and 1990, over 250 desert bighorn sheep were transplanted, establishing at least nine populations that augment four additional areas containing native populations (Cresto et al. 1990).
Buechner (1960) believed that only remnant populations persisted in the state. Utah, which has conducted aerial trend counts on bighorn since 1969 (Cresto et al. 1990), documented increasing populations statewide. Individual populations, however, have exhibited large increases and sudden declines. In 1993 the desert bighorn population was estimated at 2,200-2,250 (N. McKee and J. Karpowitz, Utah Division of Wildlife, unpublished data).
Future of Desert Bighorn
Since 1960 bighorn have increased in numbers, but their population levels are still low when compared with the estimates of pre-European numbers and the amount of available unoccupied habitat. The number of sheep in individual populations has fluctuated greatly. Population monitoring and efforts to restore desert bighorn must continue to ensure viable future populations.
		For further information: Henry E. McCutchen National Biological Service Colorado Plateau Research Station Northern Arizona University PO Box 5614 Flagstaff, AZ 86011

References
Bleich, V., J.D. Weyhausen, K.R. Jones, and R.A. Weaver. 1990. Status of bighorn sheep in California, 1989 and translocations from 1971 through 1989. Desert Bighorn Council Transactions 34:24-26. Buechner, H.K. 1960. The bighorn sheep in the United States, its past, present and future. Wildlife Monograph 4. 174 pp. Carson, B. 1941. Man, the greatest enemy of desert bighorn mountain sheep. Bull. 21, Texas Game, Fish and Oyster Commission. Austin, TX. 23 pp. Clark, R.K., and D.A. Jessup. 1992. The health of mountain sheep in the San Andres Mountains, New Mexico. Desert Bighorn Council Transactions 36:30-35. Cowan, I. McT. 1940. Distribution and variation in the native sheep of North America. American Midland Naturalist 24:505-580. Cresto, J., J. Karpowitz, and L. Seibert. 1990. Status of desert bighorn sheep in Utah, 1989. Desert Bighorn Council Transactions 34:31-32. DeForge, J.R., S.D. Osterman, D.E. Toweill, P.E. Cyrog, and E.M. Barrett. 1993. Helicopter survey of Peninsular bighorn sheep in Northern Baja California. Desert Bighorn Council Transactions 37:24-28. Delaney, D. 1989. Status of desert bighorn sheep in Nevada, 1988. Desert Bighorn Council Transactions 33:13-14. Graham, H. 1980. The impact of modern man. Pages 288-309 in G. Monson and L. Sumner, eds. The desert bighorn, its life history, ecology and management. University of Arizona Press, Tucson. Kilpatric, J. 1982. Status of desert bighorn sheep in Texas, 1982. Desert Bighorn Council Transactions 26:102-104. McCutchen, H.E. 1981. Desert bighorn zoogeography and adaptation in relation to historic land use. Wildlife Society Bull. 9:171-179.	McQuivey, R.P. 1978. The desert bighorn sheep of Nevada. Nevada Department of Wildlife Biology Bull. 6:1-81. Ramey, R.R., II. 1993. Evolutionary genetics and systematics of North American mountain sheep: implications for conservation. Ph.D. dissertation, Cornell University. 250 pp. Russo, J.P. 1956. The desert bighorn in Arizona. Arizona Game and Fish Department Wildlife Bull. 1:1-153. Sandoval, A.V. 1979. Bighorn sheep status report from New Mexico. Desert Bighorn Council Transactions 23:82-87. Seton, E.T. 1929. Lives of game animals. Vol. 3. Doubleday Page and Co., New York. 780 pp. Torres, S., V.C. Bleich, and A. Pauli. 1993. Status of bighorn sheep in Nevada, 1992. Desert Bighorn Council Transactions 37:54-55. Trefethen, J.B., ed. 1975. The wild sheep in modern North America. Boone and Crocket Club. Winchester Press, New York. 302 pp. Weaver, R.A. 1985. The status of the desert bighorn in the United States. Pages 82-85 in Manfred Hoefs, ed. Wild sheep, distribution, abundance, management and conservation of the sheep of the world and closely related mountain ungulates. Northern Wild Sheep and Goat Council Special Report. Yukon Wildlife Branch, Whitehorse, Yukon, Canada. Weaver, R.A. 1989. Status of bighorn sheep in California, 1988. Desert Bighorn Council Transactions 33:11-12. Wishart, W. 1978. Bighorn sheep. Pages 160-171 in J.L. Schmidt and D.L. Gilbert, eds. Big game of North America, ecology and management. Stackpole Books, Harrisburg, PA. Wolfe, J. 1990. Status of bighorn sheep in Colorado, 1989. Desert Bighorn Council Transactions 34:27.

References

Bleich, V., J.D. Weyhausen, K.R. Jones, and R.A. Weaver. 1990. Status of bighorn sheep in California, 1989 and translocations from 1971 through 1989. Desert Bighorn Council Transactions 34:24-26.

Buechner, H.K. 1960. The bighorn sheep in the United States, its past, present and future. Wildlife Monograph 4. 174 pp.

Carson, B. 1941. Man, the greatest enemy of desert bighorn mountain sheep. Bull. 21, Texas Game, Fish and Oyster Commission. Austin, TX. 23 pp.

Clark, R.K., and D.A. Jessup. 1992. The health of mountain sheep in the San Andres Mountains, New Mexico. Desert Bighorn Council Transactions 36:30-35.

Cowan, I. McT. 1940. Distribution and variation in the native sheep of North America. American Midland Naturalist 24:505-580.

Cresto, J., J. Karpowitz, and L. Seibert. 1990. Status of desert bighorn sheep in Utah, 1989. Desert Bighorn Council Transactions 34:31-32.

DeForge, J.R., S.D. Osterman, D.E. Toweill, P.E. Cyrog, and E.M. Barrett. 1993. Helicopter survey of Peninsular bighorn sheep in Northern Baja California. Desert Bighorn Council Transactions 37:24-28.

Delaney, D. 1989. Status of desert bighorn sheep in Nevada, 1988. Desert Bighorn Council Transactions 33:13-14.

Graham, H. 1980. The impact of modern man. Pages 288-309 in G. Monson and L. Sumner, eds. The desert bighorn, its life history, ecology and management. University of Arizona Press, Tucson.

Kilpatric, J. 1982. Status of desert bighorn sheep in Texas, 1982. Desert Bighorn Council Transactions 26:102-104.

McCutchen, H.E. 1981. Desert bighorn zoogeography and adaptation in relation to historic land use. Wildlife Society Bull. 9:171-179.

McQuivey, R.P. 1978. The desert bighorn sheep of Nevada. Nevada Department of Wildlife Biology Bull. 6:1-81.

Ramey, R.R., II. 1993. Evolutionary genetics and systematics of North American mountain sheep: implications for conservation. Ph.D. dissertation, Cornell University. 250 pp.

Russo, J.P. 1956. The desert bighorn in Arizona. Arizona Game and Fish Department Wildlife Bull. 1:1-153.

Sandoval, A.V. 1979. Bighorn sheep status report from New Mexico. Desert Bighorn Council Transactions 23:82-87.

Seton, E.T. 1929. Lives of game animals. Vol. 3. Doubleday Page and Co., New York. 780 pp.

Torres, S., V.C. Bleich, and A. Pauli. 1993. Status of bighorn sheep in Nevada, 1992. Desert Bighorn Council Transactions 37:54-55.

Trefethen, J.B., ed. 1975. The wild sheep in modern North America. Boone and Crocket Club. Winchester Press, New York. 302 pp.

Weaver, R.A. 1985. The status of the desert bighorn in the United States. Pages 82-85 in Manfred Hoefs, ed. Wild sheep, distribution, abundance, management and conservation of the sheep of the world and closely related mountain ungulates. Northern Wild Sheep and Goat Council Special Report. Yukon Wildlife Branch, Whitehorse, Yukon, Canada.

Weaver, R.A. 1989. Status of bighorn sheep in California, 1988. Desert Bighorn Council Transactions 33:11-12.

Wishart, W. 1978. Bighorn sheep. Pages 160-171 in J.L. Schmidt and D.L. Gilbert, eds. Big game of North America, ecology and management. Stackpole Books, Harrisburg, PA.

Wolfe, J. 1990. Status of bighorn sheep in Colorado, 1989. Desert Bighorn Council Transactions 34:27.

Desert Bighorn Sheep

Population Trends

Subspecies

Status and Trends by State

Future of Desert Bighorn