At their
peak, North American bighorn sheep numbers
were estimated at 2 million. Desert populations
have since fallen to about 20,000; of which
about 4,500 are found in Arizona. The causes
for this decline, which occurred primarily
between 1850 and 1900, were competition with
livestock for food and water and livestock
associated parasites and diseases.
Life History
Desert bighorns show considerable differentiation between the sexes. Adult
males weigh between 160 and 200 lbs. with a maximum weight of 225 lbs.
Adult females range from 75 to 130 lbs. and average 110 lbs. The biggest
visual difference between the two sexes is the horns. Ewe horns are generally
10 to 13 inches long with a circumference of 5 to 6 inches. Ram horns may
measure 30 to 40 inches along the outside curl with a basal circumference
of 13 to 15 inches. The horn core is honeycombed with chambers, or sinuses,
which reduce the weight of the skull.
Newborn bighorn lambs weigh 8 to 10 lbs. The young are active within minutes
after birth. The young have dark eyes and fuzzy, dark-grey hair. As they
mature, their eyes take on the characteristic golden or amber color. After
several months, they take on adult coloration; dark brown in their northern
range and pale buff in the southern. Color accents are a white muzzle,
rump patch, eye rings, and edging on the rear legs, with a black tail.
Bighorn sheep have a life expectancy of 10 to 12 years, but can reach 17
or older.
Usually one, rarely two lambs will be born. Young rams stay with their
mothers until two years of age. They then leave the nursery herds and join
in the bachelor herds. Except during the breeding season, and sometimes
during the spring when early vegetation sprouts, bighorn adults separate
according to sex. Hunt History
Totally protected by the territorial legislature in 1893, bighorn sheep
were not legal game in Arizona until 1953, when it was determined that
the limited hunting of trophy rams might be the only way to save these
animals. Two limited hunts of 20 permits each were authorized, and 20 bighorn
were taken. Since then, permit numbers, the number of units open to hunting,
the number of rams taken, and hunt success have gradually increased. About
100 rams, mostly desert bighorns, are now being taken each year. This number
will only increase, however, when the disease problem and other limiting
factors are brought under control.
Behavior
Physiological and behavioral sexual maturity varies. While rams as young
as six months may be capable of breeding, they don't, due to the dominance
of older rams. In nature, ewes probably aren't bred until they are two
and a half years old and rams don't breed until three and a half. The breeding
season extends from early June through October. Peak rutting activity occurs
in August. The gestation period is 179 days.
Bighorn sheep are diurnal animals. Females, with lambs and yearlings, usually
travel further then rams because of there being more mouths to feed. Bighorn
usually occur in small groups, but have been seen in herds of 50 or more.
In the wild, grasses are important to the bighorn. Bighorn also feed heavily
on jojoba. Pincushion and saguaro cactus provide moisture. Preferred plant
species vary with habitat quality, locality, and species availability.
Mountain lions, golden eagles, bobcats, and coyotes have all been implicated
as predators.
Summary
Breeding
Period: September-November
Young
Appear: March-April
or later
Average
Number of Young: 1-2
Distribution: 90-4,500
ft, desert ranges of
southern and western
Arizona
Habitat: Desert
mountain ledges and grassy
basins
Food
Preference: Fluff
grass, catsclaw, ocotillo
spurges, buckwheat,
mescal, janusia, slim
triodia, Indian wheat,
filaree, and weeds
in season
Habitat
