Groups of ewes stay in distinct ranges, with little interchange between groups. Rutting occurs in November and December in northern populations, and may be yearlong for desert bighorns, peaking in August and September. Gestation is 5.5-6.0 mo. Lambing season is mid-April to early June, depending on conditions. Desert bighorns may give birth at any time, but most births occur from January to April.
Twins are rare.
Ewes reach sexual maturity at 2.5 yr, possibly as yearlings under good conditions. Rams reach sexual maturity at the same age, but are unlikely to mate until larger. Extremely sensitive to disease. A herd at Lava Beds National Monument was lost to pneumonia in 1980. Diseases, particularly those of livestock, may be the major factor in decline and loss of populations.