Reproduction
All subspecies of female gorillas sexually mature in the wild between the ages of 7 to 8 and in captivity approximately 5 1/2 years old. Males sexually mature in the wild between 8 to 9 1/2 years old and in captivity as early as 6 1/2. Males are not considered fully mature until about 15 years old. Gorillas do not have a distinct breeding season. Gestation lasts from 250 to 270 days. In the wild, female gorillas usually deliver their first offspring at 10 1/2 years old and at four year intervals thereafter. One infant is normally produced and twins are rare.

Life Cycle
At birth, infants weigh 4-5 pounds (1.8-2.3 kg) and have sparse hair covering their pink-gray skin. At about nine to 10 weeks, they begin to crawl on their own and soon walk on all four limbs. A white patch of hair appears on the rump of gorilla infants at about the same time they begin to walk. The white patch helps the mother keep track of the infant and assists other group members in identifying the gorilla as an infant. The rump patch begins to disappear at about age 3, the same age that weaning usually begins. Females remain with their natal group until about age 8 or 9, then join an unrelated group or a solitary male. Males remain with their natal group until about age 12, then begin to go off on their own. Solitary males try to attract females from other groups to form their own group.

All in the Family
A family group includes one dominant silverback male, several adult females, adolescents, juveniles and infants. The group may also include one or two subordinate silverbacks. All adult males are silverbacks. Although gorillas are normally not aggressive, they can exhibit certain aggressive actions when disturbed. Adult males perform elaborate displays, including chest beating, running sideways and tearing up vegetation to frighten off an intruding male or other threat. Males also use these displays as a show of dominance within the group. Adult females can become aggressive when defending their infants, or while helping each other drive off rowdy, young adult males. The silverback is the peace keeper and stops occasional squabbles between females.

Vegetarians with Muscles
Gorillas are incredibly powerful, the largest great ape in the world. Regardless of their imposing appearance, they are in fact quite shy, gentle animals. Gorillas are virtually vegetarian and forage throughout the day in search of a variety of plants to consume. The hair of the western lowland gorilla is grayish-black and usually reddish on their head (particularly prominent in adult males). At about age 10, males begin to grow the distinctive silver-white saddle of hair on their back, which in western lowland gorillas continues to extend down the rump and thighs as the male gets older. Mountain gorillas have darker, longer hair.

Woodland Park Zoo has two gorilla groups which can be viewed at the zoo’s Tropical Rain Forest. Group 1 includes six members — a silverback male, two adult females, a subadult female, one juvenile female, and an infant female. Group 2 lives in a separate enclosure and also has six members — a silverback male, two adult females, two subadult females and one infant female.

All gorillas are endangered.* The estimated population of wild western lowland gorillas is about 110,000 and the estimated population of eastern lowland gorillas is 10,500. Mountain gorillas are the most endangered and number about 650. The primary reason gorillas are endangered is because of habitat destruction caused by logging and agricultural expansion. The bushmeat trade, facilitated by logging, has become an immediate threat to the western lowland gorilla population, particularly in Cameroon. Additionally, infection from the Ebola virus has recently become a great threat, killing many gorillas.

Woodland Park Zoo participates in the Association of Zoos & Aquariums' (AZA) Species Survival Plan (SSP) for gorillas. We have helped diversify the captive gene pool with our breeding efforts. The zoo also works to educate the public about gorillas and this is the first step to gorilla conservation.

How You Can Help!
The effort to save endangered species requires cooperation and support at the international, national, regional and individual levels. You can help in this cause. Join and become active in Woodland Park Zoo and other conservation organizations of your choice. Please do not buy products made from wild animal parts or exotic woods. Contact your elected representatives and express your views about conservation of endangered species and wild habitats.

Contact the Woodland Park Zoo at webkeeper@zoo.org to find out ways you can support conservation programs at the zoo. Discover more about endangered gorillas by contacting the World Wildlife Fund at (202) 293-4800.

Sources and Suggested Reading
Dixon, A. F. 1981. The Natural History of the Gorilla. New York Columbia University Press, New York, NY. 202 p.

Fossey, Dian. 1983. Gorillas In The Mist. Houghton Mifflin Company, Boston, MA. 326 p.

Morris Animal Foundation Mountain Gorilla Studies

Peterson, Dale. 2003. Eating Apes. University of California Press, Berkeley, CA. 320 p.

Redmond, Ian. 1995. Gorilla. Alfred A Knopf Inc., New York, NY. 63 p.

Zoobooks. 1994. Apes. Wildlife Education Ltd., San Diego, CA. 18 p.

Facts About Woodland Park Zoo's Gorillas: Group 1

Facts About Woodland Park Zoo's Gorillas: Group 2

Frequently Asked Questions About Gorillas

* Woodland Park Zoo identifies an animal or plant endangered if it is listed as endangered (in any part of its range) on the federal list of Endangered and Threatened Wildlife and Plants, or if it is listed on Appendix I to the Convention on International Trade in Endangered Species (CITES).