 Females reach sexual maturity between one @-@ and @-@ a @-@ half to three years of age . They typically average one litter every two to three years throughout their reproductive lives , though the period can be as short as one year . Females are in <unk> for about 8 days of a 23 @-@ day cycle ; the gestation period is approximately 91 days . Females are sometimes reported as monogamous , but this is uncertain and polygyny may be more common . Copulation is brief but frequent . Chronic stress can result in low reproductive rates when in captivity as well as in the field . 
