Species: Gorilla gorilla . 3 subsp. W. Lowland, E. lowland, Mountain
PHYSICAL DESCRIPTION: Male Ht. 5.2-5.9 ft., Wt. 310-400 lbs. Female Ht. 4.6-5.0 ft., Wt. 170-200 lbs. Coat: Black to brown-gray, turning gray with age. Male with broad silver saddle. Skin jet black almost from birth. Quadrupedal knuckle-walking. Longevity: about 35 years in wild.
GEOGRAPHIC LOCATION: Central Africa
ECOLOGY: Terrestrial herbivores. Prefer dense undergrowth in secondary forests. Home range: 10 km2 Day range: .5-1.0 km. Population density: variable, approx. .35-.75 / km2
DIET: Terrestrial vegetation (leaves, stems, roots), e.g., ginger, bamboo. Ants < 1%
SOCIAL ORGANIZATION: One-male polygynous groups (2-35 individuals, avg. 10), solitary males. Male and female transfer. Members of groups strongly attracted to dominant silverback male. No distinct female dominance hierarchy, no significant female ties. No territorial defense. Group forages in close proximity with minimal feeding competition. Aggression rare, limited to male-male conflicts. One quarter on infant deaths result from infanticide by males, hence protection from strange males is an important function of the group silverback.
REPRODUCTION: No birth seasonality. Males sexually mature at 15 yrs., females at 8 yrs. Gestation length: 8.6 months. No obvious estrus swellings. Litter size: 1. Interbirth interval: 4 yrs. Infant birth wt.: 5 lbs. 40% infant mortality in first 3 yrs.
PARENTAL CARE: Infants carried by females for 1-2 yrs. Walk at about 9 months. Silverback male highly protective of infants and juveniles. Weaning at 3 ys.
TOPIC OF SPECIAL INTEREST: Linguistic and cognitive abilities. "Koko," a female gorilla, acquired over 400 signs in ASL and tested at 80 on a human IQ test. She enjoyed having a kitten as a pet.
Fossey, Dian 1983. Gorillas in the mist. Boston: Houghton Mifflin.
_____ 1984. Infanticide in Mountain Gorillas. In: Infanticide, edited by G. Hausfater and S. Hrdy. Hawthorne, NY: Aldine.
Stewart, K.J. & Harcourt, A.H. 1986. Gorillas: variations in female relationships. In: Primate Societies, ed. Barb Smuts et al. Chicago: University of Chicago Press.
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