This species exhibits a promiscuous mating system. Gestation lasts about 12-14 months. One young (rarely 2) is born in spring/early summer (usually). Young are weaned in 1-2 years. The interval between successive births for an individual female is 3-5 years (though 2 years if the calf is lost early). Females are sexually mature at a minimum age of 4-5 years, though newly mature individuals often do not successfully rear young; most females breed successfully by 7-9 years. Males may be 9-10 years old before they breed, though they may attain physical maturity a few years earlier. Maximum longevity is several decades. See O'Shea and Ludlow (1992) for further details.