Animal Diversity Web

Ge­o­graphic Range

Moun­tain, or east­ern go­ril­las, Go­rilla beringei, are found in the Virunga vol­ca­noes that sep­a­rate the De­mo­c­ra­tic Re­pub­lic of Congo from Rwanda and Uganda.

• Biogeographic Regions
• ethiopian
  • native

Habi­tat

Moun­tain go­ril­las in­habit the mon­tane cloud for­est of the Virunga range. Oc­ca­sion­ally they go into the afro-alpine mead­ows (4,000 m) where tem­per­a­tures are sub­freez­ing at night and there is lit­tle suit­able food to for­age on.

• Habitat Regions
• tropical
• terrestrial

• Terrestrial Biomes
• rainforest
• mountains

• Range elevation

  4000 (high) m

  13123.36 (high) ft

Phys­i­cal De­scrip­tion

Go­ril­las are the largest pri­mate, with av­er­age lengths of 150 cm for fe­males and 185 cm for males. They are highly sex­u­ally di­mor­phic, with fe­males weigh­ing 70 to 114 kg and males av­er­ag­ing 160 kg. They have ro­bust bod­ies, long mus­cu­lar arms, short legs, mas­sive heads, and males have large, sharp ca­nine teeth. Moun­tain go­rilla coats are silky and long, rang­ing in color from blue-black to brown­ish-grey. Ma­ture males de­velop a large patch of sil­ver or grey hair on their backs, giv­ing them the name sil­ver­backs. Males also have apoc­rine glands in their armpits that emit a strong odor when the an­i­mal is under stress.

Moun­tain go­ril­las dif­fer from other go­ril­las in hav­ing longer hair, larger jaws and teeth, smaller nose, and shorter arms.

• Other Physical Features
• endothermic
• homoiothermic
• bilateral symmetry

• Sexual Dimorphism
• male larger

• Range mass

  70 to 200 kg

  154.19 to 440.53 lb

• Range length

  150 to 185 cm

  59.06 to 72.83 in

Re­pro­duc­tion

Moun­tain go­ril­las are polyg­y­nous; the dom­i­nant male in each group has ex­clu­sive ac­cess to all the fe­males in the group.

• Mating System
• polygynous

Re­pro­duc­tive rates are slow and a fe­male may leave only 2 to 6 off­spring over a 40 year life-span. Males that have a harems of 3 to 4 fe­males in­crease their re­pro­duc­tive out­put by fa­ther­ing 10 to 20 off­spring over 50 years. These an­i­mals don't ma­ture sex­u­ally until well into their teens.

Mat­ing be­hav­ior is ini­ti­ated by the fe­male, with a se­ries of slow and hes­i­tant ap­proaches to the male. A fe­male is re­cep­tive only dur­ing es­trus, and she will cease to ovu­late for sev­eral years after giv­ing birth. The length of the es­trous cycle of a fe­male moun­tain go­rilla is 28 days, and there is no vis­i­ble ex­ter­nal men­strual flow.

A sin­gle, de­pen­dent young is born after a eight and a half month ges­ta­tion pe­riod. Wean­ing often doesn't occur until three years of age, and ju­ve­niles may re­main with moth­ers for years after that. Fe­males are sex­u­ally ma­ture by 10 years of age, but males are un­likely to start breed­ing be­fore 15 years. Re­pro­duc­tive out­put for fe­males is about one sur­viv­ing off­spring every 8 years (sur­vival im­ply­ing reach­ing breed­ing age).

• Key Reproductive Features
• iteroparous
• year-round breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual
• fertilization
• viviparous

• Breeding interval

  The interval between reproductive events depends upon infant survival. Females are capable of producing an infant every 4 to 5 years.

• Breeding season

  These animals breed throughout the year.

• Average number of offspring

  1

• Average gestation period

  8.5 months

• Range weaning age

  36 to 48 months

• Average age at sexual or reproductive maturity (female)

  10 years

• Average age at sexual or reproductive maturity (male)

  15 years

Fe­males pro­vide most of the parental care in this species. Fe­males nurse and carry their young for about 4 years. They also play with the young, teach them, and groom them.

The role of males in parental care is less di­rect, al­though no less im­por­tant. Males pro­tect the fe­males and the young within their so­cial group from po­ten­tially in­fan­ti­ci­dal rival males who may take con­trol of the group.

• Parental Investment
• altricial
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • male
    • female
• pre-weaning/fledging
  • provisioning
    • female
  • protecting
    • male
    • female
• pre-independence
  • protecting
    • male
    • female
• extended period of juvenile learning

Lifes­pan/Longevity

Go­ril­las can reach ages of 40 to 50 years.

• Typical lifespan
  Status: wild

  50 (high) years

Be­hav­ior

The main so­cial unit is a male with a harem of fe­males and their off­spring. These groups are non­ter­ri­to­r­ial, but se­vere in­ter­group con­flicts can occur when groups en­counter each other and es­pe­cially if a lone male con­tacts the group. The dom­i­nant male of a group is mas­sive com­pared to the other mem­bers and they all defer to him.

Fe­males trans­fer from their natal group to a new group be­fore breed­ing. This gen­er­ally oc­curs at around 8 years of age. Often they join a lone male and start a new group, rather than join an es­tab­lished group and be a lower rank­ing fe­male. Males often leave the natal group at around 11 years of age. Males, how­ever, can't join an es­tab­lish group, and they spend much time in soli­tary ex­is­tence until they can gain fe­males and begin a group of their own at age 15 or older.

Groom­ing often oc­curs be­tween fe­males and males, or among fe­males.

Go­ril­las spend about 30% of the day feed­ing, 30% trav­el­ing, and 40% rest­ing. They make nests to sleep and rest in that can be in trees, on steep slopes or even on the ground.

• Key Behaviors
• terricolous
• diurnal
• motile
• sedentary
• social
• dominance hierarchies

Com­mu­ni­ca­tion and Per­cep­tion

All pri­mates have com­plex pat­terns of com­mu­ni­ca­tion. Go­ril­las are known to use vo­cal­iza­tions to com­mu­ni­cate with one an­other. Tac­tile com­mu­ni­ca­tion, in the form of groom­ing, play, and sex­ual con­tact, also oc­curs. Males emit a strong odor when stressed, which ap­pears to func­tion as a type of chem­i­cal com­mu­ni­ca­tion. In ad­di­tion to these, go­ril­las use body pos­tures and fa­cial ex­pres­sions, as well as other vi­sual sig­nals, to com­mu­ni­cate with one an­other.

• Communication Channels
• visual
• tactile
• acoustic
• chemical

• Perception Channels
• visual
• tactile
• acoustic
• chemical

Food Habits

Moun­tain go­ril­las oc­ca­sion­ally eat in­ver­te­brates, but they are pri­mar­ily fo­liv­o­rous. They eat the roots, leaves, stems, and pith of herbs, vines, shrubs, and bam­boo. Their diet is sup­ple­mented by small amounts of bark, wood, roots, flow­ers, fruit, fungi, ep­ithe­lium stripped from roots, galls, in­ver­te­brates, and go­rilla dung.

• Primary Diet
• herbivore
  • folivore

• Animal Foods
• insects

• Plant Foods
• leaves
• roots and tubers
• wood, bark, or stems
• fruit

• Other Foods
• fungus
• dung

Pre­da­tion

These an­i­mals are very large, and live in re­gions where not many po­ten­tial preda­tors exist. It is not likely that they fall prey to any par­tic­u­lar species with any reg­u­lar­ity.

Ecosys­tem Roles

These an­i­mals may be im­por­tant in struc­tur­ing plant com­mu­ni­ties, as they feed heav­ily on veg­e­ta­tion.

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

Go­ril­las may be vis­ited by eco­tourists, en­hanc­ing local economies.

• Positive Impacts
• body parts are source of valuable material
• ecotourism
• research and education

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

There is con­tin­u­ing po­lit­i­cal pres­sure to con­vert the re­main­ing go­rilla re­serves into areas for farm­ing or com­mer­cial use. Due to the high pop­u­la­tion den­sity, many peo­ple feel that the land would be bet­ter put to com­mer­cial use.

Con­ser­va­tion Sta­tus

Moun­tain go­ril­las are highly en­dan­gered. This is due both to habi­tat de­struc­tion and se­vere poach­ing pres­sures. Go­rilla species are sub­jected to heavy pres­sure from poach­ing for body parts and for young an­i­mals col­lected for zoos and pri­vate col­lec­tions, gen­er­at­ing il­le­gal in­come. The civil war oc­cur­ring in the re­gion they in­habit has only added to their plight, in­creas­ing mor­tal­ity through ac­ci­dents and the break­down of pa­trol units against poach­ers.

• IUCN Red List

  Critically Endangered
  More information

• IUCN Red List

  Critically Endangered
  More information

• US Federal List

  Endangered

• CITES

  Appendix I

Other Com­ments

Go­ril­las are usu­ally very gen­tle crea­tures. Their only ef­fec­tive preda­tors are hu­mans. They are often thought to be "slow" or "dumb" be­cause of their slug­gish­ness, but in fact they are in­tel­li­gent and ca­pa­ble of learn­ing sign lan­guage.

There is an on­go­ing de­bate as to the re­la­tion­ship of go­ril­las, chimps and hu­mans. Go­ril­las are clearly one of our clos­est rel­a­tives if not the clos­est, shar­ing 98% of our genome.

Con­trib­u­tors

Nancy Shef­ferly (ed­i­tor), An­i­mal Di­ver­sity Web.

Tracy Lind­s­ley (au­thor), Uni­ver­sity of Michi­gan-Ann Arbor, Anna Bess Sorin (au­thor), Bi­ol­ogy Dept., Uni­ver­sity of Mem­phis.

Ref­er­ences

Estes, R.D. 1991. The Be­hav­ior Guide to African Mam­mals. Uni­ver­sity of Cal­i­for­nia Press: Los An­ge­les.

Mit­ter­meier, Rus­sell A. and Dorothy L. Ch­eney. 1987. Con­ser­va­tion of Pri­mates and Their Habi­tats. Pri­mate So­ci­eties. 189- 202.

Watts, David P. 1994. Ag­nos­tic re­la­tion­ships be­tween fe­male moun­tain go­ril­las. Be­hav­ioral Eco­log­i­cal So­cio­bi­ol­ogy, vol.34. 347-358.

Watts, David P. 1990. Ecol­ogy of go­ril­las and its re­la­tion to fe­male trans­fer in moun­tain go­ril­las. In­ter­na­tional Jour­nal of Pri­ma­tol­ogy, vol.11. 21-43.

Stew­art, Kelly J. and Alexan­der H. Har­court. 1986. Go­ril­las: Vari­a­tion in Fe­male Re­la­tion­ships. Pri­mate So­ci­eties. 155-164.

Blaf­fer Hrdy, Sarah and Pa­tri­cia L. Whit­ten. 1986. Pat­tern­ing of Sex­ual Ac­tiv­ity. Pri­mate So­ci­eties. 370- 384.