Gorillas

Taxonomic Classification: Gorillas come from the family Pongidae.  Their genus and species is the Gorilla gorilla.

Common Name: Gorilla

Physical Description: Female gorillas weigh 70-90 kg (200lbs)and have a height of 4.5 feet, males can weigh up to 200 kg (400lbs) and have a height of 5.5 feet; males are more robust.  Gorillas’ molar teeth have a greater development than any other hominid.  Gorillas have the same number of teeth as humans, and also go through a set of ‘baby teeth’ and adult teeth.  Males have large tusk-like caninies and relatively small incisors as they mature.  Both genders have large, strong teeth to chew the coarse vegatation they consume.  Their snouts are relatively long.  Gorilla hands are very broad and their forelimbs are longer, while their torsos are short and broad.  They have a wider thorax and a basin-like pelvis; these great apes are quadrupedal.  Amung the species, mountain gorillas very rarely climb trees, while lowland gorillas (females & offspring especially) are more arboreal. The brain size for gorillas averages around 500 cc’s, and males may have a larger capacity.

Geographic Location & Range: Gorillas are normally divided into three geographically isolated subspecies, the western lowland gorilla, eastern lowland gorilla, and the mountain gorilla.  The western lowland gorilla inhabit the tropical forests of Cameroon, Central African Republic, Congo, Gabon, and Equatorial Guinea.  Eastern lowland gorillas inhabit the tropical forests of eastern Zaire.  Mountain gorillas inhabit the high altitude tropical forests of Zaire, Rwanda, and Uganda.

Diet: Gorillas depend on the vegetation in their habitat because plants and fruit make up most of their diet since they are herbivores.  They eat about 97 different plant species. Fruit takes up 67% of their diet while leaves, seeds and stems take up around 17% of their diet.  Gorillas also eat some termites and caterpillars which make up a miniscule 3% of their diet. Although gorillas live in different areas their diets tend to stay around the same percent. However, some gorillas do eat different amounts of plant species depending on their habitat and what is available for them.

Social Organization: A band of gorillas can be as small as a few individuals to upwards of thirty.  One dominant adult male often watch over the group and have their pick of the females in it – these are the silverbacks.  Occasionally a few smaller males will follow and help protect the young and the females.  Rarely, groups with larger numbers are known to have two silverbacks.  The groups have a polygamous mating system.  When male gorillas reach adolescence, they venture away from their “birth groups” and have a few choices: they can form “bachelor groups” with other male gorillas, they can attract females to form their own bands, or they can stay with their original groups.  If a younger male wishes to claim dominance over a group, it must fight the silverback and the loser must leave.  The silverback retains his females by giving attention to their offspring, effectively fighting off other males, and physical ability.  Gorillas roam around without clear territorial spots, and do not threaten off other bands that come within their area.

Reproduction: Female gorillas have a predictable reproductive cycle that usually lasts for about a month. There are no physical signs associated with this, but behavioral cues are given to the surrounding males. The gestation period is around nine and a half months.  The interbirth interval is about four years, with an average of one surviving offspring every eight years.

Parental Care: Once born, babies will nurse for a year. They remain dependent on their mothers until they reach sexual maturity, which for females is between seven and ten years, and for males is around fifteen. Male gorillas don’t take an active role in the care of their young, but they do provide group protection and show a high level of tolerance to infants and juveniles.  Infanticide is common as rival males don’t want to see any others’ offspring survive.

Language/Communication Abilities: Several sounds make-up the language of gorillas.  Hooting by a member of the band signals an alarm or an unusual event is occuring.  If a silverback hoots, this attracts attention from every member imediately.  Sharp grunts amung gorillas are used to disipline the young.  To signify pleasure, low growls are used.  Every gorilla beats its chest, but in males this is used to show power or to intimidate.  If trained, gorillas have been known to master over one hundred words in sign language.

Evidence of Culture: During the long dependancy stage of young gorillas, their mothers teach them everything they must know to be independant; such as making nests, finding food, etc.  Differences between species are mostly due to availablity in food resources.  For example, western lowland gorillas eat mainly fruit while mountain gorillas eat foliage.  There are only minor differences in the groups of the same species, however.  Gorillas in zoos adapt to their environment, and some (in large enough groups to develop group norms) have been reported to pull food into their enclosures with sticks.  Research on multiple groups in the wild are few, however.

Works Cited:

  • “GORILLAS – Diet & Eating Habits.” SeaWorld/Busch Gardens ANIMALS – HOME. Web. 26 Sept. 2010. <http://www.seaworld.org/animal-info/info-books/gorilla/diet.htm>.
  • Foley, J. (1997, April 28). Gorilla skull. Retrieved on 27 Sept. 2010.  <http://www.talkorigins.org/faqs/homs/gorilla.html>.
  • Grzimek, Bernhard, Neil Schlager, and Donna Olendorf. Grzimek’s Animal Life Encyclopedia. 2nd ed. Vol. 14. Detroit: Gale, 2003. Print. Mammals II.
  • Gorillas. (2002). Magill’s encyclopedia of science: animal life. Pasadena, CA: Salem Press, Inc.
  • Primate Societies. Chicago, IL: University of Chicago Press, 1987. Print
  • W C McGrew.  (1998).  Culture in nonhuman primates?  Annual Review of Anthropology, 27, 301-328.      Retrieved September 26, 2010, from Social Science Module.

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One Response to Gorillas

  1. Megan M. says:

    Looks good! My favorite subspecies of gorilla is the Western Lowland Gorilla, just because it’s full name is Gorilla gorilla gorilla.

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