The eastern lowland gorilla (Gorilla beringei graueri) or Grauer's gorilla
The eastern lowland gorilla (Gorilla beringei graueri) or Grauer's gorilla is a Critically Endangered subspecies of eastern gorilla endemic to the mountainous forests of eastern Democratic Republic of the Congo. Important populations of this gorilla live in the Kahuzi-Biega and Maiko National Parks and their adjacent forests, the Tayna Gorilla Reserve, the Usala forest and on the Itombwe Massif.
It is the largest of the four gorilla subspecies. It has a jet black coat like the mountain gorilla (Gorilla beringei beringei), although the hair is shorter on the head and body. The male's coat, like that of other gorillas, greys as the animal matures, resulting in the designation "silverback".
Habitat area
Gorilla beringei graueri is a subspecies of the eastern gorilla. Gorilla beringei graueri is less endangered than the mountain gorilla, with a population of 5,000 individuals. The subspecies is distributed in lowland and montane subalpine forests in eastern Democratic Republic of Congo, southwestern Uganda, Rwanda and the area between the Lualaba River and lakes Edouard and Tanganyika.
Appearance
The beringei graueri gorilla has a large head, broad chest, long legs and a large flat nose. Its fur is mostly black, and mature males have a silver stripe on the back. The coat covers almost the entire body, except for the face, chest, palms of the hands and feet. With age, it becomes greyish in colour. Adult males weigh an average of 160 kg and can reach 220 kg; females weigh between 70 and 114 kg; body length is 185 cm for males and 150 cm for females.
Nutrition and lifestyle
Beringei graueri gorillas prefer forests with dense grass cover. They feed on roots, leaves, bark, wood, flowers, fruits and stems of plants, and sometimes on invertebrate animals and fungi. Like the western lowland gorilla, these great apes live in family groups consisting of a dominant male, several females and cubs, but the group size of the beringei graueri gorilla is larger than that of the western apes, with an average of 35 individuals.
Group boundaries are not guarded, but skirmishes may occur when one group encounters another. Females often move from their native group to another before the mating season. This usually occurs around 8 years of age. They often join single males and create a new group. Males leave the family they have grown up with at the age of 11. They spend a lot of time alone and usually do not form their own family until they are 15 years old.
Reproduction
There is no defined breeding period for Gorilla beringei graueri. Females give birth to cubs only once every 3-4 years, due to the long period of gestation and rearing of the young. Pregnancy lasts 8.5 months, after which a cub is born. Newborns have greyish-pink skin and can crawl at 9 weeks after birth. Weaning occurs at 3.5 years of age. Sexual maturity occurs at 10 years in females and 15 years in males.
The life expectancy of the Gorilla beringei graueri is 40-50 years.
Number
The number of Gorilla beringei graueri in 1995 was estimated at 16,900 animals. In the last decade it has declined considerably. The range of this subspecies is 21,600 km², 25% less than in 1969. Agriculture is an important survival factor for Gorilla beringei graueri. Current political instability and the killing of gorillas for their meat add to the problem of their protection. The subspecies is included in the IUCN Red List with the status Endangered.
