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Bighorn Sheep (Ovis canadensis) Fact Sheet: Reproduction & Development

Bighorn Sheep (Ovis canadensis)

Courtship

  • Estrus cycle averages 28 days and female is receptive for 48 hours.
  • Females are estimated to produce lambs between the ages of 2 to 16.
  • Males have been documented as breeding successfully as young as 6 months of age. (Turner & Hansen 1980). Larger rams would control this in the wild.
  • Rams routinely check estrus status of ewes by flehmen (urine-testing), and they can stimulate females to urinate by licking the vulva.
  • Rut (term designating the breeding period) occurs in late summer and fall.
  • Male begin courtship when a female is in estrous with a series of contact patterns (twist, nose, kick, chest push).
  • Females courtship is exhibited by the rubbing their body and horns on the male.
  • Dominant males gain priority over females but subordinate males still attempt to mount estrous females.
  • A ewe in estrous will often be pursued by numerous rams
  • Mating and lambing seasons of desert species are extended because of unpredictability of rain and forage availability.

Reproduction

  • Birth rates and lamb survival vary with the quality of food supply available
  • Rates vary significantly among ewe groups in the desert region from 8 lambs: 100 ewes to 100 lambs: 100 ewes
  • Breeding and parturition periods of desert bighorns more lengthy than northern species. (May be due to unpredictable food supply)
  • Twinning is rare in all bighorn sheep
  • As the ewes age, there is a decrease in their fertility
  • Sexual maturity (Wilson and Mittermeier 2015)
    • Males: by 1.5 years old
      • Males over 5 years old do most of the breeding
    • Females: typically mate at 2.5 years (girth birth when 3 years old)

Gestation and Birth

Gestation

  • Generally accepted as 6 months (171-185 days)

Birth

  • Ewes select an isolated, sheltered site with unobstructed view to give birth.
  • Lambing season (greatest number of lamb births) is generally between February through August.
  • Usually single young are born, but twins have been recorded
  • Neonates are precocial and often called “followers”.
  • After a few weeks of not being seen, the mother rejoins the herd and put the lamb in a community nursery with other lambs.

Life Stages

Infants (<1 year of age)

  • Body weight in newborns is 8-10 lbs.
  • Body length at birth: 420 mm (16.5 inches)
  • Young lambs are a grayish coloration with soft hooves and a black-brown tail.

Weaning

  • Lambs are weaned by 6 months of age.

Juveniles (1-2 years of age)

  • Body weight is 41-50 kg (90-110 lb) (females) to 52-59 kg (115-130 lb) (males)
  • Body length is 690 mm (27 in) (females) to 915 mm (36 in) (males)
  • Yearling ram horn is much like adult ewe horn but thicker at the base and blue-gray.
  • Female horns are 125-178 mm long, thin and sharp-pointed.

Subadults (2-3 years of age)

  • Body weight is 45.8 kg (101 lb)(females) to 69.4 kg (153 lb) (males)
  • Body length is 851 mm (33.5 in) (females) to 991 mm (39 in) (males)

Young adults (4-5 years of age)

  • Body weight is 55.6 kg (122.6 lb) (females) to 64.9 kg (143 lb) (males)
  • Body length is 965 mm (38 in) (females) to 977 mm (39in) (males)

Adults (>5 years of age)

  • Body weight is 57.2 kg (126 lb) (females) to 78.5 kg (173 lb) (males).
  • Body length is 876 mm (34.5 in) (females) to 1010 mm (39.8 in) (males)
  • Ram adults have a large knob on the back of their head, often calloused and without hair while younger rams often have no knob.
  • Permanent dentition is in place after four years of age.
  • Sexual maturity (Wilson and Mittermeier 2015)
    • Males: by 1.5 years old
      • Males over 5 years old do most of the breeding
    • Females: typically mate at 2.5 years (girth birth when 3 years old)

 

 

Longevity

  • Males: Many rams live 9-12 years.
  • Females: Ewes may live 10-14 years.

Mortality and Health

  • 1971 study of Desert Bighorn mortality in Arizona and southeastern Nevada: poaching 41%, road kills 20%, natural accidents 15%, drownings 12%, fence mortalities 12%.
  • Precipitous 52% population decline in 1988-89 in Arizona due to livestock viral disease and nutritional stress
  • Other documented threats in Arizona: automobile collisions, coyote/mountain lion predation

Bighorn Sheep Ewe and Lamb

Bighorned sheep mother and young

Young lambs are a grayish coloration with soft hooves and a black-brown tail.

Image credit: © San Diego Zoo Global. All rights reserved.

Page Citations

Turner & Hansen (1980)
Shackleton (1984)
USFWS (2000)
Thompson & Turner (1982)

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