© 2005-2019 Rocky Mountain Bighorn Society
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
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