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  The Mammals of Texas - Online Edition

Mountain Sheep
Order Artiodactyla : Family Bovidae : Ovis canadensis Shaw

Mountain Sheep (Ovis canadensis).  Photo by John L. Tveten.Description. A large, dark-brown sheep with heavy, tapering, curled brown horns in males (horns much smaller and less curled in females), and conspicuous white rump patch; pelage hairy, not woolly; four black hoofs on each foot; tail short; mammae two. Dental formula: I 0/3, C 0/1, Pm 3/3, M 3/3 X 2 = 32 (lower canine is shaped like an incisor). External measurements average: (males) total length, 1,763 mm; tail, 107 mm; hind foot, 439 mm; (females) 1,431-107-407 mm. Weight of rams, 75-150 kg; females, 45-65 kg.

Distribution in Texas. Formerly ranged throughout the isolated mountain ranges of the Trans-Pecos; however, native populations are now extirpated. The last native sheep were seen in the Sierra Diablo in 1959, when the total population was estimated at 14. Recent introductions of mountain sheep (or "bighorn sheep") in the Sierra Diablo, Van Horn Mountains, Elephant Mountain Wildlife Management Area, and Baylor Mountains have resulted in small, wild populations in these areas.

Habits. In general, mountain sheep are inhabitants of rough, rocky, mountainous terrain. They are not forest dwellers but prefer bluffs and steep slopes where the vegetation is sparse and the view unobstructed.

Beds are conspicuous indicators of the presence of sheep. Two distinct types are utilized. The day bed, used during midday siestas, is a temporary affair constructed when and where the individual sheep decides to rest. Usually, each adult animal, particularly among the rams, excavates a shallow depression by executing three or four pawing scratches with each forefoot before lying down. Lambs and yearlings usually omit the pawing activity. The night beds are more elaborate structures. They are usually situated on steep, rocky slopes, on top of rocky rims, or on a slope between two bluffs. In such places the sheep receive adequate protection, for they have an unobstructed view in all directions except uphill, from which direction the approach of a predator would be signaled by rolling stones. The animals tend to bunch together at night. Individual beds are ovoid in shape with the long axis on the contour of the slope. Beds are typically 7-10 cm in depth, about 75 cm in length, and 60 cm in width. No bedding of any sort is utilized; the animals lie on the bare earth. Beds in constant use are rimmed with piles of feces and strong with the odor of urine.

The food of bighorn sheep depends on availability and season. In western Texas deer brush, sotol, and ocotillo were utilized extensively by bighorns. Vernon Bailey reported them as feeding on mountain mahogany, Mexican tea, trumpet flower, mock orange, prickly pear, wild onions, and penstemon. The fruits of datil (Yucca) and prickly pear are especially choice foods in the desert areas. Bighorns rarely need water. Apparently, they derive sufficient water from the green and succulent vegetation on which they feed.

The breeding season begins in November and continues for a period of approximately 6 weeks. The rams do considerable fighting at this period, and usually the larger and stronger ones prevent the weaker ones from mating. The bighorn ram does not assemble and guard a harem but moves from flock to flock seeking ewes that are ready to mate. Ewes become sexually mature in 2 years and give birth to their first lambs at 3 years of age. Rams under 3 years of age appear to take little, if any, active part in breeding activities. The gestation period is approximately 180 days. The first lambs are born in mid-May with others appearing until about mid-June. Usually, only one lamb is produced, but twins are not infrequent. The lambs are weak and helpless at first but they develop rapidly and by the age of 1 week are able to follow the ewes about with ease.

Age in mountain sheep can be estimated by examination of the teeth. The formula at birth is I 0/3, C 0/1, Pm 2/2, M 0/0 (milk dentition); at 8 months, I 0/3, C 0/1, Pm 3/3, M 1/1 (molars permanent); at 15-18 months, I 0/3, C 0/1, Pm 3/3, M 2/2 (molars permanent); 24 months, first (middle) incisor is shed and replaced by permanent tooth; 36 months, first two premolars are shed and replaced by permanent teeth; 42 months, third molars are fully erupted, second milk incisor replaced, last premolars shed and replaced; 48 months, full set of permanent teeth.

At one time bighorn sheep were widespread in Trans-Pecos Texas but the advance of civilization and the inroads of domestic sheep upon the range of the wild animals led to a steady decline of the bighorn population. In spite of laws affording full protection to the sheep, they continued to decline in numbers. Today, the native population is extinct. The Texas Parks and Wildlife Department is attempting to establish wild-trapped sheep from other states in several Trans-Pecos mountain ranges. The 1990 population estimates for these herds were as follows: Van Horn, 25; Baylor, 18; Elephant Mountain, 31; Sierra Diablo, 127. In addition, 27 sheep were released on Beach Mountain in 1991.

Photo credit: John L. Tveten.