The western gorilla (Gorilla gorilla) is a great ape found in Africa, one of two species of the hominine genus Gorilla. Large and robust with males weighing around 168 kilograms (370 lb), the species is found in a region of midwest Africa, geographically isolated from the eastern gorilla (Gorilla beringei). The hair of the western species is significantly lighter in color.
The western gorilla is the second largest living primate after the eastern gorilla. Two subspecies are recognised: the western lowland gorilla (Gorilla gorilla gorilla) is found in most of West Africa; while the Cross River gorilla (Gorilla gorilla diehli) is limited to a smaller range in the north at the border of Cameroon and Nigeria. Both subspecies are listed Critically Endangered.
Western gorillas are generally lighter colored than eastern gorillas. Western gorillas have black, dark grey or dark brown-grey hair with a brownish forehead. Males average 167 cm (5 ft 6 in) although reaching a height up to 176 cm (5 ft 9 in), with males weighing 145 to 191 kilograms (320 to 421 lb) and females weighing 58 to 72 kilograms (128 to 159 lb).[7] Captive western gorillas average 157 kg (346 lb) in males and 80 kg (176 lb) in females.[8] Another source[which?] describes the weight of wild male western lowland gorillas as 146 kg (322 lb).[9] The Cross River gorilla differs from the western lowland gorilla in both skull and tooth dimensions.
Western gorillas live in groups that vary in size from two to twenty individuals. Such groups are composed of at least one male, several females and their offspring. A dominant male silverback heads the group, with younger males usually leaving the group when they reach maturity. Females transfer to another group before breeding, which begins at eight to nine years old; they care for their young infants for the first three to four years of their lives. The interval between births, therefore, is long, which partly explains the slow population growth rates that make the western gorilla so vulnerable to poaching. Due to the long gestation time, long period of parental care, and infant mortality, a female gorilla will only give birth to an offspring that survives to maturity every six to eight years. Western gorillas are long-lived and may survive for as long as 40 years in the wild. A group's home range may be as large as 30 km2 (12 sq mi), but is not actively defended. Wild western gorillas are known to use tools.