Mature males develop a large patch of silver or grey hair on their backs, giving them the name silverbacks. Males also have apocrine glands in their armpits that emit a strong odor when the animal is under stress. They eat the roots, leaves, stems, and pith of herbs, vines, shrubs, and bamboo. Reproduction Reproductive rates are slow and a female may leave only 2-6 offspring over a 40 year life span. These animals don't mature sexually until well into their teens.
Mating behavior is begun by the female, with a series of slow and hesitant approaches to the male.
A female is receptive only during estrus, and she will cease to ovulate for several years after reproducing. The length of the estrous cycle of a female mountain gorilla is 28 days, and there is no visible external menstrual flow. A single, dependent young is born after a eight and a half month gestation period. Weaning often doesn't occur until three years of age, and juveniles may remain with mothers for years after that. Females are sexually mature by 10 years of age, but males are unlikely to start breeding before 15 years.