Taxonomic lineage

Genus Gorilla belongs family Hominidae (great apes) together with Pan (chimpanzee), Homo (human), and Pongo (orangutan). The orangutan is the most primitive of great apes and is separated in the subfamily Ponginae. Thus, great hominoid trio consists of Homo, Pan and Gorilla. With chimpanzee being closest human relative, gorilla is the next. Gorilla is a largest of all primates.

cellular organisms - Eukaryota - Fungi/Metazoa group - Metazoa - Eumetazoa - Bilateria - Coelomata - Deuterostomia - Chordata - Craniata - Vertebrata - Gnathostomata - Teleostomi - Euteleostomi - Sarcopterygii - Tetrapoda - Amniota - Mammalia - Theria - Eutheria - Euarchontoglires - Primates - Haplorrhini - Simiiformes - Catarrhini - Hominoidea - Hominidae - Homininae - Gorilla - Gorilla gorilla

Subspecies

Gorilla gorilla diehli (Cross river gorilla)
Gorilla gorilla gorilla (Western lowland gorilla)
Gorilla gorilla uellensis

Brief facts

• Distribution

  The western lowland gorilla population consists of approximately 30,000 individuals and spans an area from the west coast of Africa, including Gabon, Equatorial Guinea, the southeastern tip of Nigeria, and Cameroon, to the southwest corner of the Central African Republic. Cross River gorillas are very rare (approx. 200 individuals). Some 600 miles of forest of the Congo basin separate the western lowland gorilla from the eastern populations that include eastern lowland and mountain gorillas (Gorilla beringei).

• Appearance

  Western lowland gorillas are smaller than mountain gorilla, have shorter hair with a shade of brown and more prominent underlying scalp pad. Unlike mountain gorillas they can climb trees.

• Habitat

  Gorilla gorilla inhabit Africa's tropical lowland forests with dense undergrowth. Direct observations in this habitat are very difficult and the species are poorly studied. The exception to this are studies based in large swampy clearings ("bais"), which provide an unobstructed view of the animals. Bais are located in the forest of northern Republic of Congo, specifically in Nouabale-Ndoki National Park and Odzala National Park (marked with pin on the map).

• Nesting

  One study found that 26% of gorilla nests are arboreal, and the rest are ground sleeping sites, with or without nest construction. The most common type of ground nests built by gorillas are herbaceous (45%), followed by woody and mixed nests (13% and 7%, respectively). Minimalistic nests or bare sleeping sites constitute less than 5%. The average height of arboreal gorilla nests is 5-14 meters, which is much lower than that of nests built by sympatric chimpanzees (10-26 m). Ninety six percent of gorilla nests are found in mixed species forest. Gilbertiodendron and flooded forests are avoided. Gorilla prefer nesting in closed understory habitats (80-90% of all nests).

• Diet

  Western lowland gorilla diet consists of more than 100 species of various plants. The fruit and seed of at least 95 species, and the leaves, stems, shoots, bark or flowers of about 50 species are consumed. Western lowland gorillas depend on seasonally available fruits in their diet to much greater degree than mountain gorillas and therefore experience spacial and temporal variation in diet which affects structure and dynamics of their society. The commonest herbaceous plant of family Marantaceae (arrowroot or prayer-plant family) and Zingiberaceae (ginger family) known for their starchy rhizomes are a major food source for gorillas. Gorillas avoid fatty fruit and oily seeds and prefer ripe sugary ones like those from Pentadesma butyracea (commonly known as butter, tallow tree or candle tree). During periods of fruit scarcity, they increase their use of terrestrial and aquatic (from bais) herbaceous vegetation. Gorilla diet overlaps greatly with that of sympatric, frugivorous primates such as guenons (Cercopithecus spp), mandrills (Mandrillus sphinx) and chimpanzees. What distinguishes them is their ability to eat large fibrous fruit, mature leaves and stems, and to overcome high levels of phenols and condensed tannins in their diet. Gorillas greatly facilitate seed dispersal in the tropical forests.

• Population structure

  Single-male group with several (1-5) adult females accompanied by infants and immature individuals is main unit of western lowland gorillas' society. Average group size varies in different studies and ranges from 6 to 14 individuals. The following group types are recognized: nascent, infant, juvenile, mature, and senescent. Rest of the population consists of disintegrating groups that lost their silverback and lone males that may be in the process of recruiting females. Groups that contain only males are rare.

• Females

  Gorillas are unusual among mammals in having social system characterized by female-biased dispersal, which is shared with red colobus, hamadryas baboons and Thomas's langurs. Both natal and secondary females transfers occur. One study have shown that natal emigration accounts for most transfers (37%). Thirty percent of emigrations were caused by death of the group leading silverback after which group members gradually disperse and join other bands in small groups or singularly. In this case pregnant and nursing females transfer involuntary and run the risk of losing their infants to infanticide by male in destination group. Secondary female emigrations also occur after loss of infant and when the group becomes too large for a given female's preference. The mean length of female tenure in a group varies widely from 3 months to up to 6.4 years.

• Sexual behavior

  Females exhibit mild genital swelling in periods of optimal receptivity. The males are usually unobtrusive in soliciting copulation whereas females are positively assertive and actively seek sexual attention from leading silverbacks. Gorillas use dorsal-ventral (rear entry) as well as ventral-ventral mating positions. Females can mate "strategically" throughout estrous cycle and even during pregnancy.

• Gestural communications

  Gesture is defined as a discrete limb or head movement of a "signaler" that is directed to another individual ("receiver") and appears to covey either the signaler's intentions or signaler's "wish" toward the receiver. According to the dominant theory for the origin of gestural communication in great apes (Call and Tomasello, 2007), the repertoire of an ape can be divided into two parts: species-specific "hard-wired" gestures and non-species-typical gestures acquired in the process called ontogenetic ritualization. Gestures can be divided into three categories: silent, audible and tactile. Silent visual gestures are usually directed to attentive audience, audible and tactile gestures slightly less so. Western gorilla's repertoire of gestures among all captive apes and primates studied has been found the largest, both in total and per individual. Idiosyncratic gestures are rare, and may be associated with solitary, playful gesturing. Some "cultural" differences between gesture usage and presence of group-specific sets of gestures have been recorded in gorillas.
  Examples of species-specific gestures used by gorillas:
  
  • Body tapping - tapping own body part with palm.
  • Bow - bending forward upper body while standing on two legs.
  • Chest beat playful - drumming playfully on chest with palms.
  • Stamp - stamping the ground forcefully with sole of foot, often following or simultaneous with chest beat.
  • Chest beat aggressive - beating chest forcefully with fists.
  • Clap - clapping palms as if in applause.
  • Drum other - drumming another individual with palms of hands.
  • Gallop - running with forelegs playfully stamping the floor.
  • Ice skating - twirling movement of whole body around the body y axis while standing on four legs.
  • Look - staring intensively at another individual for several seconds.
  • Pirouette - twirling movement of whole body around the body y axis while standing on four legs.
  • Stiff walk or gallop - walking or galloping with rigid forelegs.

• Conservation status

  In September 2007, the World Conservation Union (IUCN) issued new Red List where western lowland gorilla was placed into critically endangered category. IUCN experts found that the western gorilla population has declined by 60% in the past decades and estimated that Ebola hemorrhagic fever has killed at least one third of animals living in protected areas such as national parks.

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Life history

Interbirth interval is about 4-5 years.

• Prenatal
  • Embryo MeSH Average gestation period is about 257 days (Cross & Martin, 1981; Meder, 1939).
• Post natal
  • Neonate
  • Infant Until weaning. Weaning typically occurs around 36-48 months of age. Dependent infants are most vulnerable to infanticide when the protector male (its putative father in most cases) is absent.
  • Juvenile Between 3 and 6 years of age.
  • Subadult Or adolescent. Between 6 an 8 years old.
  • Adult Males between 8 and 12 years are blackbacks (nearing full body size, lacking full coloration and complete sagittal crest development), between 12 and 15 years are young silverbacks, and silverbacks from 15 years old. Sexual maturity is attained at about 8-10 years of age in females and 15 years in males. Adult gorilla exhibit marked sexual dimorphism. In the wild, male gorillas average 180 kg, with females often almost half that weight. Male gorillas stand usually about 1.75 meters tall with bent knees. Wild gorillas live between 35 and 40 years with some captive gorillas living almost 50 years.

Western lowland gorilla at National Zoo (Washington, D.C.)

11/27/2010

Female (if you don't see the video below)

Young male (if you don't see the video below)

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References

• Gross L. Wild Gorillas Handy with a Stick. PLoS Biol. 2005 November; 3(11): e385.

  

  A first time for everything: This adult female gorilla in Nouabalé-Ndoki National Park, northern Congo, uses a branch as a walking stick to gauge the water's depth, proving that gorillas use tools too.

• Breuer T, Ndoundou-Hockemba M, Fishlock V. First observation of tool use in wild gorillas. PLoS Biol. 2005 Nov;3(11):e380.

  

  Female Efi Using Trunk as a Stabilizer during Food Processing at Mbeli Bai The top photo shows the intact trunk shortly before Efi manipulated it (visible to the left of female Fulani). The trunk was then detached by female Efi with both hands (middle), pushed into the ground, and used as a stabilizing stick while dredging aquatic herbs towards her with her other hand (bottom).

• Stokes EJ, Parnell RJ and Olejniczak C. Female dispersal and reproductive success in wild western lowland gorillas ( Gorilla gorilla gorilla). Behavioral Ecology and Sociobiology. Volume 54, Number 4, 329-339
• Nadler RD. Sexual cyclicity in captive lowland gorillas. Science. 1975 Sep 5;189(4205):813-4.
• Vigilant L, Bradley BJ. Gorillas. Curr Biol. 2004 Oct 5;14(19):R826-7.
• Doran-Sheehy DM, Fernández D, Borries C. The strategic use of sex in wild female western gorillas. Am J Primatol. 2009 Dec;71(12):1011-20.
• Yamagiwa J, Kahekwa J, Basabose AK. Infanticide and social flexibility in the genus Gorilla. Primates. 2009 Oct;50(4):293-303.
• Gatti S, Levréro F, Ménard N, Gautier-Hion A. Population and group structure of western lowland gorillas (Gorilla gorilla gorilla) at Lokoué, Republic of Congo. Am J Primatol. 2004 Jul;63(3):111-23.
• Parnell RJ. Group size and structure in western lowland gorillas (Gorilla gorilla gorilla) at Mbeli Bai, Republic of Congo. Am J Primatol. 2002 Apr;56(4):193-206.
• Robbins MM et al. Social structure and life-history patterns in western gorillas (Gorilla gorilla gorilla). Am J Primatol. 2004 Oct;64(2):145-59.
• Stokes EJ. Within-group social relationships among females and adult males in wild western lowland gorillas (Gorilla gorilla gorilla). Am J Primatol. 2004 Oct;64(2):233-46.
• Vogel G. Conservation. Scientists say Ebola has pushed western gorillas to the brink. Science. 2007 Sep 14;317(5844):1484.
• Genty E, Breuer T, Hobaiter C, Byrne RW. Gestural communication of the gorilla (Gorilla gorilla): repertoire, intentionality and possible origins. Anim Cogn. 2009 May;12(3):527-46.
• Sanz C et al. Distinguishing between the nests of sympatric chimpanzees and gorillas Am Nat. 2007 May;169(5):684-9.
• Rogers, M. E., Maisels, F., Williamson, E. A., Fernandez, M. & others. (1990). Gorilla diet in the Lope Reserve, Gabon - a nutritional analysis. Oecologia. 84: 326-339.
• Csomos, R. 2008. "Gorilla gorilla" (On-line), Animal Diversity Web. Accessed August 29, 2010
• Popovich, D.G. and E.S. Dierenfeld (1997) Gorilla Nutrition. In: Management of Gorillas in Captivity: Husbandry Manual, Gorilla Species Survival Plan. J. Ogden and D. Wharton, Eds. American Association of Zoos and Aquariums. (.pdf)
• Walsh PD, Breuer T, Sanz C, Morgan D, Doran-Sheehy D. Potential for Ebola transmission between gorilla and chimpanzee social groups. Journal of Applied Ecology 2007 44, 263–272. (.pdf)
• Tanner JE & Byrne RW. Representation of action through iconic gesture in a captive lowland gorilla. Current Anthropology, 37(1), 162-173. (.pdf)

Images credit: http://kotomatrix.ru/