Males compete for access to females during the fall breeding season, or rut. This occurs in October and early November. During this time males may engage in battles that leave them injured and exhausted. Dominant males restrict access to small groups of 5 to 15 females. Males stop feeding during this time and may lose weight rapidly.
Mating System: polygynous
In late August and September, prime bulls shed the velvet that surrounds their antlers. Fighting among males (sparring) begins shortly after that, with the rut (breeding season) usually occurring in October. Females can breed as early as 16 months of age but usually begin to breed at 28 months. With good nutrition females give birth to calves each year, but may skip years in areas with low quality forage. A single calf, weighing 3 to 12 kg, is born after about 228 days, in May or June. Twins have been reported, but are rare. Calves are weaned during the first week of July, but also begin to graze on grasses soon after birth. Calves rely mainly on grazing for nutrition after 45 days old.
Breeding interval: Caribou breed once yearly.
Breeding season: Breeding typically occurs in October.
Range number of offspring: 2 (high) .
Average number of offspring: 1.
Average gestation period: 7.6 months.
Average weaning age: 1.5 months.
Range age at sexual or reproductive maturity (female): 16 (low) months.
Average age at sexual or reproductive maturity (female): 28 months.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); viviparous
Average birth mass: 6500 g.
Average gestation period: 228 days.
Average number of offspring: 1.
Average age at sexual or reproductive maturity (male)
Sex: male: 680 days.
Newborn calves are precocial, being able to suckle minutes after birth, follow their mother after an hour and are capable of outrunning a human at one day of age. Calves nurse exclusively for their first month, after which they begin to graze. They will continue to nurse occasionally through early fall, when they become independent.
Parental Investment: no parental involvement; precocial ; pre-fertilization (Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female)