Kingdom: Animal
    Phylum: Chordata
        Class: Mammalia
            Order: Primates
                Family: Hominidae
                    Subfamily: Homininae
                        Genus: Gorilla
                            Species: Gorilla gorilla (Western gorilla)
                                Subspecies: Gorilla gorilla gorilla (except in Cross River area)
                                Subspecies: Gorilla gorilla diehli (Cross River population)
                            Species: Gorilla beringei (Eastern gorilla)
                                Subspecies: Gorilla beringei beringei (Virunga mountain gorillas)
                                Subspecies: Gorilla beringei graueri (Eastern lowland)
                                Subspecies: Gorilla beringei ? (Bwindi forest population)
                        Genus: Homo
                            Species: Homo sapiens
                        Genus: Pan
                            Species: Pan paniscus
                            Species: Pan troglodytes
                    Subfamily: Ponginae
                        Genus: Pongo
                            Species: Pongo abelii (Sumatran orangutan)
                            Species: Pongo pygmaeus (Bornean orangutan)

• IUCN Primate Specialist Group acknowledges 2 species (eastern and western)
  - 2 groups are 1,000 km apart
  - Re-evaluation by Groves 2001 suggests 5 subspecies
• A group of 250-300 individuals around the Cross River differs from the western lowland subspecies in skull and tooth dimensions, and was designated a unique subspecies in 2000

• Closest relative: Pan (Chimpanzee) 
• Humans, chimpanzees and gorillas share a common ancestor not shared by orangutans (Groves 2000).
• Molecular studies by Ruvolo indicate substantial distance between eastern and western species. Diverged 2 million years ago.
 

• Western gorillas are found throughout west and central Africa: (most widespread species) southwestern Central African Republic, western Congo, Angola (Cabinda province), Gabon, Equatorial Guinea, southern Cameroon, southeastern Nigeria
  - Cross River Population (most northern & western population) are on both sides of Nigeria-Cameroon border at head waters of Cross River - 10 fragmented areas
  - Density highest where their staple food is most abundant
  - Home ranges vary and overlap
• Eastern gorillas found in East-Central African region: eastern D.R. Congo, southwestern Uganda, northern Rwanda.

• Submontane and lowland areas
• Prefer dense primary forests/undisturbed secondary forests with dependable, year-round food supply of high-quality herbs
• Visit open swampy areas ("bais") that are filled with aquatic and semi-aquatic sedges - different groups share bais
• May nest along savanna forest edges

Weight: M 135-600 lbs (135-275 kg) F 150-310 lbs (70-140 kg)
Height: 4 - 5.75 ft (1.25 - 1.75 m)

Pelage: 

• Gray-brown/black. Top of head is reddish-brown. Skin is black
• Mature male has "silver" back from shoulders to rump
• Eastern gorillas are somewhat larger than western gorillas - longer faces and
  broader chests. Blacker hair

Sexual Dimorphism: Adult male is almost twice the size of the female

Other Physical Characteristics: Gorillas are the largest primate

• More field studies of eastern (mountain) gorillas than western species
  -Western species have been difficult to habituate because they're more hunted
  -Schaller 1959-1961 mountain gorilla study
  -Karisoke Research Center established by Dian Fossey in 1967 to study Virunga mountain gorillas in Rwanda. (Fossey was murdered in 1985 but studies continue)

• Diurnal - forage on ground from daybreak to nightfall (females and young may climb, feed and sleep in trees)
• Morning and afternoon feeding periods with a long mid-day rest in between. (This pattern is also seen in chimpanzees and other monkeys)
  -Morning feeding is intense - at least 2 hours
  -Weather influences length of rest period (longer on cooler days) A nest is usually not constructed
  -Afternoon feeding more prolonged but less intense
• When little fruit is available, energy is conserved by decreasing range and feeding on lower quality herbs
• Travel ~1-3 km / day
  - Travel farther when forests have more fruit and termites.
  - Larger groups must travel farther to secure sufficient food for the group
  - Human hunters and leopards affect travel
• Nest building begins after afternoon feeding - up to an hour before dusk. Silverback initiates process. Nest on ground or in trees - used for one night only

• ~7-14 sq km
• No territory defense - groups overlap. Encounters involve vocal exchanges and chest-beating.
• Ranging areas of neighboring gorilla groups overlap extensively
• Groups frequently enter auditory range of each other but avoid contact

• Most diurnal primates live in groups because of predation threats
• Group size: ~4-6 adults and children (2-32)
• Composition: Dominant male silverback, 3-4 females and young (larger groups have a higher proportion of adult females)
• Female social relationships influenced by relatedness.
  - Indifference/hostility toward non-kin
  - Grooming rarely observed between adult females
• Maturing males usually leave natal group in late adolescence - may take females with them
  - Remain solitary until they can establish their own group
  - Multi-male groups rare. (More common in mountain gorillas)
• Many females also transfer between groups
  - Voluntary transfer from natal (8-9 years of age)
  - Involuntary transfer: female joins new male after only silverback has died
  - May consecutively join different groups
• Temporary division of groups into subgroups that stay apart for several days.

• Little aggression among members of the same group. Silverback maintains peace
• Includes fixed stare, thrusting head toward antagonist, bluff charges, roaring
• Silverbacks may exchange explosive displays - chest beating, hooting
  - ritualized display beginning with series of soft hoots, escalating to climax
  - facilitated by air sac within chest that resonates when inflated
  - animal rises up to bipedal position just before climax
  - running, slapping/tearing/throwing vegetation can occur
• Severe fights between adult males can occur
  - effort to gain/retain mates and protect offspring
  - scars and wounds common
  - no fighting over food
• Infanticide infrequent (so far, observed among Virunga gorillas, after death of protector male) (Fossey, 1984)

• All gorillas >2.5 years build nests for sleeping at night and sometimes for mid-day rest
• Usually built on level ground. Vegetation is folded around and under the body. (Some nests built in trees)
• Adult male nest = 5 x 5 feet or 5 x 4 feet (oval)
• Entire process takes ~1-3 minutes
• Sometimes sleep on bare ground
• Nest counts are often used to determine population size
• Chimpanzees and orangutans also build nests

• Most commonly seen in infants beginning around 4-5 months of age
  - Lone play - Running, climbing, shredding leaves, slapping vegetation
  - Social play - wrestling, mock biting
• Diminishes around 6 years of age

• Mutual grooming uncommon - Some mother-child, female-silverback
• Females compete with one another for social access to males - Silverback intervenes to stop conflicts.
• Visual Signs: facial expressions
• Vocalizations: At least 22 distinct sounds: grunts, barks, screams, hoots
  - Hoots may be contact calls to communicate forest location
• Olfaction/Scent Marking: gorilla 'fear odor' (the scent of scared gorillas) has been detected in the air after encounters between western gorillas and leopards (Fay, 1995)

• Quadrupedal knuckle walking.
• Cautious tree-climbers (mainly juveniles, females and infants)
• No brachiation
• No swimming - ford streams 1-2 ft deep but not deeper or wider waters

• Eat many of the same foods as chimpanzees and elephants- competition for resources but no agonistic encounters observed.
• Flee from leopards / humans

• Opportunistic - Depends on plant availability (season, geography and altitude)
• Must consume large quantities since leaves / plants offer little nourishment
• Vegetable diet probably meets water requirement - not observed to drink in wild

• Folivore-frugivore - up to 230 items and 180 plant species
• Highly selective - fruit & seeds favored, stems, pith & leaves
• High-quality herbs of the Marantacae genera: Megaphrynium, Haumania, Marantochloa, Halopegia, Hydrocharis
• Aquatic and semiaquatic vegetation found in "bais" is highly digestible, high in protein, salt, and minerals. (Cyperaceae and Gramineae families)
• Leguminous tree Gilbertiodendron dewevrei produces seeds every 5 years. Gorillas will travel some distance for the seeds
• In absence of preferred foods: roots, bark, low-quality herbs: Aframomum, Palisota
• Aframomum is a potent antibacterial, antiviral, antifungal and anti-inflammatory 'natural drug,' Might be preventive medicine as much as food.
• 20 species of invertebrates (mainly termites & ants)
• Mountain gorillas are totally folivorous. Chimpanzees are mainly frugivorous
• Wild gorillas are strictly vegetarian but captive gorillas will readily eat meat

• Enlarged hindgut associated with colic-cecal fermentation
• Cecums contain large number of cellulose-digesting ciliates
• Long gut retention time allows maximum absorption of nutrients
• Mountain gorilla's teeth adapted for shearing leaves; strong jaws for repetitive chewing. Western gorilla teeth have enlarged post-canine dentition but more like chimpanzees (both are frugivorous)

• Some food preferences may be "learned" (insects eaten vary with different populations)
• Tend to choose vegetation high in protein, low in fiber
• Avoid leaves high in condensed tannins

• Male: Complete copulation by age 9-10 years but few mating opportunities until Silverback status ~ 12-15
• Female: Perineal tumescence observed in the field ~5.7-7.1 years
  After 2 years of adolescent sterility, first birth - 8.5-10 years.

• Disease & Mortality Rates vary between populations
• Susceptible to same diseases as humans: common cold, pneumonia, yellow fever, tuberculosis, bacterial meningitis, measles, rubella, mumps, chicken pox
• Yaws (Treponema pertenue) causes tissue necrosis
• Ebola virus struck one study population in 2004 (400 gorillas in Odzala-Kokous National Park, Republic of Congo)
  - 97% of group-dwelling individuals, 77% of solitary males died.
  - 95% of the population disappeared in one year.
• Respiratory disease not reported for western gorillas (often fatal for mountain gorillas)
• Susceptibility to spondyloarthropathy (erosive arthritis). Found in 20% of wild gorillas
• Predation by leopards

• Adult western lowland gorillas in captivity are dying of an unexplained heart condition called fibrosing cardiomyopathy - treated with pacemakers / heart drugs
• Prone to periodontal disease, which is linked to heart problems in humans; bacteria from gum infections can cause inflammation elsewhere in the body, including the heart.

• In 1855 a traveling menagerie exhibited the first gorilla outside of Africa as a chimpanzee
• The Berlin Aquarium briefly exhibited a single gorilla in1876 and again in1883
• The first gorilla in North America was an infant male that died after 5 days in Boston in 1897
• The first zoo to exhibit a gorilla was the Bronx Zoo, importing animals in 1911 and 1914.  But in 1915 William Hornaday, the zoo director, wrote, "There is not the slightest reason to hope that an adult gorilla ever will be seen living in a zoological park or garden."
• ISIS: 329 males 416 females 10 unknown all western lowland
  Antwerp has 2 female eastern lowland gorillas
• Female gorilla Koko has been taught American Sign Language at the Gorilla Foundation.  She can understand ~2000 words and can make ~1,000 ASL signs.

• 41 percent of deaths of captive gorillas - and 70 percent of deaths of the males older than 30 - are the result of heart disease, primarily fibrosing cardiomyopathy. (Heart muscle turns into fibrous bands unable to pump blood)
• Gorillas are also prone to periodontal disease. (Bacteria from gum infections can cause inflammation elsewhere in the body, including the heart).

• ISIS captive population 
• Gorilla gorilla gorilla (except in Cross River area)
  - Status: Endangered
  - Population trend: Down by 50% in Gabon a previous stronghold, but new population of 125,000 in Congo discovered in 2008.
  - Current estimates: 175,000 to 225,000
• Gorilla gorilla diehli (Cross River population)
  - Status: Critically Endangered
  - Current estimate: 220
• Gorilla beringei beringei (Virunga mountain gorillas)
  - Status: Critically Endangered
  - Population trend: Up from 620 in 1989
  - Current estimate: 700
• Gorilla beringei graueri (Eastern lowland)
  - Status: Endangered
  - Population trend: Down from about 17,000 in mid-1990s
  - Current estimate: 2,000 - 3,000
• Gorilla beringei ? (Bwindi forest population)

• Traditional protected areas protects against hunting, habitat loss
• Great Ape Survival Project (GRASP) links the 23 ape range-state governments with all the different organizations working for great apes and various United Nations programs

• Bulk of western population lives outside protected areas
• Habitat loss - deforestation (agriculture, logging, domestic animal grazing)
• Killed by farmers in retaliation for crop-raiding
• Accidental death from snares
• Civil war (80-90% of eastern lowland gorillas disappeared in Congo fighting 2002-2005
• Small isolated populations susceptible to being wiped out by disease
• War and civil unrest has resulted in human encroachment
• Gorilla ecotourism started in Rwanda and Uganda in the 1960s can bring disease - hepatits A, poliovirus, tapeworm, TB bacillus
• Bushmeat, trophy & subsistence hunting
• Coltan, a mineral used in cell phones, is found in gorilla habitat in the eastern Democratic Republic of the Congo. Miners in the area eat gorilla meat

• GRASP Great Apes Survival Project
• An extensive bibliography associated with the World Atlas of Great Apes and their Conservation, 2005 is available here:  
• Gorilla Ethogram