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

• 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.

• 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

• 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.
  

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)

Wild populations

• Males: Many rams live 9-12 years.

• Females: Ewes may live 10-14 years.

Managed care

• Peninsular bighorn sheep (Ovis canadensis nelsoni)
  • Median life expectancy (AZA 2023)
    • Males: no AZA estimate
    • Females: 10.3 years

• Disease transmission from domestic animals possible (Kamath et al. 2019)
  • See Phys.org story
• 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

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

Image credit: © San Diego Zoo Wildlife Alliance. All rights reserved.

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