Shortly before mating season begins, females exhibit swelling of the sex skin, which reaches its peak around the middle of their 14.8 day estrous cycle. Male sexual physiology also undergoes its own change, with testicular volume increasing during mating season and peaking around the time of breeding. Aggression also increases during the mating season, both between members of the same sex and by the female towards the male attempting to mate with her. Females have been observed grappling, cuffing, and biting males during copulation. Either sex may approach the other when the female is in estrus. Initially they may "roar-shriek" with each other. When a male approaches a female, he often lowers his head and squeals, inspecting the female's genitalia by licking or sniffing, scent-marking, and offering a submissive chattering vocalization. When a female approaches a male, she may posture herself for mounting. Mating pairs often copulate many times during the course of a mating bout.