Sheep Biology
By Christopher Roe, Certified Wildlife Biologist
Bighorn sheep are arguably one of the most recognizable hoofed animals in the
western United States, if not in all of North America. Consisting of several
races, or varieties, bighorn sheep are distinguished from their northern
cousins (thinhorned sheep) by their heavier, blockier bodies, and more massive
horns, which often have broken or "broomed" tips. Heavily ridged and massive
horns curling back, downward, and up into the classic "full curl" make the
mature bighorn ram truly a sight to behold.
Adult bighorn sheep typically weigh between 110 and 275 pounds (50-125 kg) and
are approximately 30 to 44 inches (75-110 cm) tall at the shoulder, depending
on the sex and age of the animal. Hair coat usually ranges from a dusty tan in
summer to dark brown or chocolate in winter. The characteristic white or gray
rump patch remains throughout the year. Horns of rams are significantly larger
than ewes, even at an early age. Rams develop significant horn mass within the
first several years, and obtain most of their horn growth within their first
7-8 years. After 7-8 years, horn growth slows with the brooming of horn tips
becoming increasingly noticeable as the years progress.
Although sexually mature at a young age, ewes typically do not bear young until
2-3 years of age and rams (especially in populations with many mature rams)
typically do not breed until they are much older. Breeding occurs in late
autumn with ewes giving birth to a single lamb in early to mid summer. Twin
lambs are uncommon.
Bighorn sheep are gregarious, social animals that typically show high fidelity
to their chosen home range. Throughout much of the year, mature rams typically
separate themselves from groups of ewes and lambs, and from bands of immature
rams. Only during the breeding season, and on some winter ranges, do you find a
mix of sexes and age classes for prolonged periods.
Bighorn sheep are active throughout the day, with several periods of foraging
interspersed with periods of grooming, sleeping, and/or playing (often ewes
with young lambs and lambs with one another). Although typically associated
with rough, rocky, open terrain, bighorn sheep can be found on alpine slopes
above tree line to the shrub and timber covered canyon lands of lower
elevations.
Several varieties, or races, of bighorn sheep can be found in western North
America. Rocky Mountain bighorns (Ovis canadensis canadensis) can be found
throughout the Rocky Mountains; from Canada to southern New Mexico, from the
western Dakotas to parts of Washington and Oregon. Desert bighorns (of which
there are four separate varieties, Ovis canadensis nelsonii, O. c. mexicana, O.
c. weemsi, and O. c. cremnobates) can be found throughout the desert southwest
of the United States in portions of Colorado, New Mexico, Arizona, Utah,
Nevada, and California, and in northwestern portions Mexico. Another separation
in bighorn sheep has been made in the case of the California bighorn (Ovis
canadensis californiana), although this classification has been contested in
recent years. Regardless of their classification, these animals have a range
similar to Desert bighorns, which include a few small areas in the states of
Oregon and Washington.
