Gorilla Facts: Chest Beats, Nests and Numbers

• The heaviest primates alive. Adult male gorillas, the silverbacks, can weigh over 400 pounds and stand between 5.5 and 6 feet tall. They weigh only about 4 pounds at birth.
• Chest beating is an honest advertisement of body size, not a bluff. Across 25 wild silverbacks studied in Rwanda's Volcanoes National Park, the beats of larger males had significantly lower peak frequencies than those of smaller males.
• The beat is a long-distance broadcast. This multimodal signal can be heard more than a kilometre away through dense forest, and is performed most often by adult males.
• Tool use in wild gorillas went unrecorded until 9 October 2004. An adult female named Leah picked up a branch and used it to test the depth of a pool at Mbeli Bai, a swampy forest clearing in northern Congo, then leaned on it as a walking stick.
• They hum and sing over particular meals. Wild western lowland gorillas at Mondika (Republic of Congo) produce two distinct food-associated calls, humming and singing, but mostly the adult males, and only while feeding on certain foods (18 of 41 plant species in their diet, plus two insect species).
• Every gorilla has a unique nose print. The wrinkle pattern above the nostrils differs between individuals, and, like other primates, each gorilla also has distinctive fingerprints.
• Quiet animals with a sizeable vocabulary. Scientists have heard up to 22 different gorilla vocalisations, each apparently carrying its own meaning.
• Pregnancy runs about 256 days. That is roughly eight and a half months, only a few weeks shorter than a human pregnancy.
• An adult male eats up to 40 pounds (18 kg) of plant food a day. Treat that as an estimate rather than a measured ration: the Smithsonian's National Zoo puts an adult male nearer 45 pounds a day, and the Dian Fossey Gorilla Fund says silverbacks can take up to 60 pounds of vegetation.
• A new bed every day. Gorillas build a fresh nest on the ground every day, using it for daytime rest and for sleeping at night; infants share their mother's nest until about age 3 or 4.
• The nests double as tree nurseries. Gorillas deposit more than half of their faeces, and therefore half of the seeds they disperse, at their nesting sites. At one Cameroon study site (La Belgique), seeds of at least 58 plant species were found in gorilla faeces.
• One subspecies has genuinely recovered. On 14 November 2018 the mountain gorilla moved from Critically Endangered to Endangered on the IUCN Red List, after climbing from about 680 animals in 2008 to more than 1,000.
• The world holds 1,063 mountain gorillas: 604 counted in the Virunga Massif and 459 in the Bwindi-Sarambwe ecosystem. This is the number usually quoted as "how many gorillas are left", but it covers one of four subspecies, confined to two forest blocks straddling Rwanda, Uganda and the DR Congo. Other gorillas number in the hundreds of thousands.
• Grauer's gorilla, the largest subspecies, fell 77% in one generation. From roughly 16,900 animals before the 1996 civil war in eastern DR Congo to about 3,800 today.
• The Cross River gorilla is the most threatened ape in Africa: fewer than 300 survive across nine sites in a roughly 12,000 km² mountainous area straddling the Nigeria–Cameroon border.
• Around 360,000 gorillas lived in the forests of Western Equatorial Africa as of 2013, according to the first range-wide count of the western lowland gorilla, published in Science Advances in 2018. The size of that number is not reassurance: the same survey found the population dropping about 2.7% a year, and the subspecies remains Critically Endangered.
• Ebola is a gorilla disease as well as a human one. Two studied Ebola epizootics in the Republic of Congo, at Lossi sanctuary (2002–03) and at Lokoué in Odzala-Kokoua National Park (2004), killed an estimated 90–95% of the gorillas in the affected populations.
• Human and gorilla DNA differ by about 1.6%. Close, but not the closest: chimpanzees and bonobos differ from us by about 1.2%.

"Gorillas beat their chests with clenched fists." Gorillas strike with the palms of their hands, not closed fists. Using palms is less likely to injure the animal and creates a louder noise that carries much further through the forest.

"Gorillas are ferocious brutes that attack people on sight." Gorillas are overwhelmingly herbivorous and, in the fund's words, "typically gentle and peaceful... not aggressive and tend to avoid conflict." Chest beating is a signal — it can express aggression, occurs in play, and encodes the caller's body size — rather than a prelude to attack.

"You can go and see a mountain gorilla at a good zoo." Not one, anywhere, ever. Every gorilla in every zoo on Earth is a lowland gorilla, almost always a western lowland gorilla. Attempts in the 1960s and 70s to build a captive mountain gorilla population killed adults to seize infants, and none of the infants survived. To see a mountain gorilla you have to go to Rwanda, Uganda or the DR Congo.

"Gorillas are our closest living relatives." Chimpanzees and bonobos are. Human DNA differs from chimp and bonobo DNA by about 1.2%, and from gorilla DNA by about 1.6%. The gorilla lineage split from ours several million years before the chimp lineage did: gorillas are cousins, not siblings.

"There are only about a thousand gorillas left in the world." That figure describes mountain gorillas alone, 1,063 at the last count. The western lowland gorilla, the one in zoos and documentaries, numbered around 360,000 in 2013. It is still Critically Endangered, because the population is falling roughly 2.7% every year, but "a thousand left" conflates one subspecies with the whole genus.

Almost every gorilla in popular culture descends from one film. King Kong premiered in New York on 2 March 1933, co-directed by Merian C. Cooper and Ernest B. Schoedsack with stop-motion animation by Willis O'Brien, and it fixed the gorilla in the public mind as a rampaging monster. The science has spent ninety years undoing that image.

Real gorillas got their own star turn in 1967, when National Geographic ran "Snowflake, the world's first white gorilla", turning a Barcelona albino into a global celebrity. In 1988 Michael Apted's Gorillas in the Mist cast Sigourney Weaver as Dian Fossey, drew five Academy Award nominations and made mountain gorilla conservation a mainstream cause.

Smaller stories have kept the animal in view since. Jersey Zoo's Jambo became the subject of the documentary Gerald Durrell: Jambo the Gentle Giant in 2005. Katherine Applegate's 2012 novel The One and Only Ivan, based on a real gorilla, was filmed in 2020. And Harambe, shot in Cincinnati in 2016, became one of the internet's longest-running memes.

Colo was born at the Columbus Zoo on 22 December 1956, the first gorilla ever born in a zoo. She died on 17 January 2017 at the age of 60, the oldest gorilla on record.

Snowflake, the only known albino gorilla, arrived at Barcelona Zoo on 1 November 1966 and died in 2003 of a skin cancer linked to his lack of pigment. Koko learned a modified sign language under Francine "Penny" Patterson and died on 19 June 2018, aged 46.

Jambo, a silverback at Jersey Zoo, stood guard over an unconscious five-year-old boy who fell into his enclosure on 31 August 1986. Ivan spent nearly three decades in a Tacoma shopping mall before moving to Zoo Atlanta in October 1994; he died on 20 August 2012, aged 50. Harambe was shot at Cincinnati Zoo on 28 May 2016.