Desert Bighorn Sheep - California Department of Fish and Game (original) (raw)
Desert Bighorn Sheep Facts
Desert Bighorn Ewe (2008)
Scientific Name
Ovis canadensis nelsoni
Size
Length: 5 feet
Height: 2 ½ – 3 ¼ feet (at shoulders)
Weight: Adult Male (Ram) 120 – 220 pounds; Adult Female (Ewe) 100 – 155 pounds
Life Span
Rams 10 – 13 years maximum; Ewes 12 – 20 years maximum
Description
In Californa, the desert bighorn, Ovis canadensis nelsoni, is found in the dry, desert mountains of southeastern California. The most evident feature of desert bighorn sheep is the large curled brown horns that continue to grow throughout their lives. Both rams (males) and ewes (females) have horns, though the horns of rams are much larger and more curved. The horns are permanent and consist of a sheath of keratin (a hard protein found in fingernails and hair) covering a boney core. By the time a ram is seven or eight, he can have a set of horns with a full curl, a spread of 30 inches, and a skull and horn weight of 20 pounds or more. Horn size is a symbol of rank among males. Many rams break off the ends of their horns (called "brooming"), often during horn clashes for dominance. Ewes are smaller than rams and have shorter, less massive horns that never exceed half a curl. Desert bighorn ewes grow longer and larger horns than Sierra Nevada or Rocky Mountain females. Bighorn coat color varies among bighorn sheep. The coat is typically dark brown or gray, while it tends toward lighter in some animals. The large white rump, strongly constrasting with the body color, often aids people in spotting sheep from a distance.
The desert bighorn is most active during daylight, often moving to steeper terrain to bed at night. During the summer bighorn sheep rest during the hottest part of the day, usually under some form of shade.
Desert bighorn sheep detect predators primarily with very keen eyesight and escape them through great agility in steep rocky slopes (escape terrain).
Life History
White Mountain Lamb (2008)
Bighorn sheep are gregarious, typically forming herds, rarely exceeding 20 individuals. During periods of scarce water and food they sometimes can be found alone. For much of the year, adult rams are segregated from ewes and the young in separate bachelor bands.
Rams engage in battles to determine dominance. Dominance is expressed via visual displays. Dominance interactions include displacement from a bedding site, kicking, butting, neck wrestling, and fights; horn clashes are the most widely known of these interactions. A horn clash can sound like a rifle shot, and can be heard for long distances during battles. The most dominant rams are typically those with the largest bodies and horns. Dominance allows mating access to estrous females. Rutting activity usually peaks in August and September but can occur over a six month period or longer. Bighorn sheep follow a poygynous mating strategy whereby the dominant males do most of the breeding.
Bighorn sheep have approximately a six-month gestation period with most ewes giving birth to one lamb per year. Twins are relatively rare. The peak of lambing is usually from February through March, but births can occur from mid-December through mid-May, and may occur during any month of the year. Lambing seasons vary significantly among mountain ranges. Lambs are very mobile within a few days of birth. Lambs are tyically weaned by five months of age.
Lamb survival varies greatly in the desert, depending on rainfall and forage growth. Lamb survival may be as low as 10% or as high as 80%. Ewes generally first breed as yearlings in most desert populations if nutrition is adequate. Males reach sexual maturity at the same age, but are not able to establish dominance until they are older (often five or older).
Range
Desert bighorn live throughout the inter-mountain west in a large number of desert mountain ranges, in eastern California, much of Nevada, northwestern Arizona, New Mexico, southern Utah, southern Colorado, and Mexico.
Habitat
Bighorn sheep favor open terrain in order to use their acute eyesite to avoid predators. They generally avoid dense vegetation that blocks visibility. Typical desert bighorn terrain is rough, rocky and steep; it also encompasses springs and plateaus. This type of terrain minimizes predation risk through easy access to escape terrain adjacent to areas where more forage may be available. They can move over level ground at 30 mph and up mountain slopes at 15 mph. They are aided by cloven hooves that are sharp-edged, elastic, and convex with a soft pliable inner pad.
Food Habitats and Nutrition
Desert bighorn sheep are ruminant herbivores. Their digestive system allows them digest a variety of forages. Their diet includes cacti (food and water), grasses, herbaceous plants, shrubs, and a few trees. They are very selective feeders that choose the most nutritious forage available. New plant growth is the most nutritious, although this varies by species. Consequently, diet composition varies by season. During periods of elevated nutrient intake, nutritional reserves (fat) can be restored for use during leaner periods and for reproduction.
Water is important to bighorn sheep survival. Bighorn sheep obtain a considerable amount of water from the forage they eat; this varies with the season. During hotter periods they visit springs or water sources at least every third day.
Hunting
Hunting of desert bighorn sheep is managed by DFG.
Management and Conservation
Management of desert bighorn sheep by DFG is coordinated with other governmental agencies and non-governmental organizations.
Major Threats
Desert sheep in California have seen a large amount of extirpation over the past 100 years. In areas where they are present, wild horses and burros compete with desert bighorns for water and forage Bighorn are extremely susceptible to disease. Like the native humans with whom they shared the southwest for thousands of years, bighorn have little resistance to the diseases of European sheep and cattle. Disease contracted from domestic livestock may be a major factor in decline and loss of some populations. Threats to habitat include vegetation succession, loss of water sources, and fragmentation. Other threats include: predation, human development small population size (causing increased effects from weather, climate, and other unpredictable natural events), and inbreeding depression (low genetic diversity).