Animal Info - Gorilla

(Other Names: 大猩猩, ゴリラ, Cross River Gorilla, Eastern Gorilla, Eastern Lowland Gorilla, Gorila, Gorille, Grauer's Gorilla, Makaku, Mountain Gorilla, Western Gorilla, Western Lowland Gorilla)

Gorilla gorilla

(Note: On the basis of recent DNA studies, the IUCN now recognizes two species of gorilla: 

1.) Eastern Gorilla (Gorilla beringei) (includes the Mountain Gorilla (G. b. berengei) and the Eastern Lowland Gorilla (Grauer's Gorilla) (G. b. graueri)); and
2.) Western Gorilla (Gorilla gorilla) (includes the Cross River Gorilla (G. g. diehli) and the Western Lowland Gorilla (G. g. gorilla)). See Taxonomy below.)

Status: Endangered

Contents

1. Profile (Picture)
2. Tidbits
3. Status and Trends (IUCN Status, Countries Where Currently Found, Taxonomy, Population Estimates, History of Distribution, Threats and Reasons for Decline)
4. Data on Biology and Ecology (Weight & Size, Habitat, Age to Maturity, Gestation Period, Birth Season, Birth Rate, Early Development, Dispersal, Maximum Age, Diet, Behavior, Social Organization, Age and Gender Distribution, Mortality and Survival, Density and Range)
5. References

Profile

Pictures: Gorilla #1 (29 Kb JPEG), Gorilla #2 (38 Kb JPEG), Gorilla #3 (48 Kb JPEG) (National Zoo)

The gorilla is the largest primate, weighing as much as 275 kg (600 lb). Gorillas are forest-associated animals. Most gorillas inhabit lowland tropical rainforests and montane rainforests between 1500 - 3500 m (4900 - 11,500 ft). Different populations have exhibited preferences for forest margins, secondary forest, swamp forests, bamboo forests, riverine forests and primary forest. The diets of the eastern and western gorilla populations differ considerably. Eastern animals are predominantly folivorous, but those in the west eat great quantities of fruit. Gorillas spend most of their time foraging on the ground, although young animals and females, particularly lowland gorillas, frequently feed and sleep in trees. Gorillas are diurnal, with nearly all activity occurring between 6:00 in the morning and 6:00 in the evening. Before nightfall, they settle into their nests which are freshly constructed each night. Gorillas live in groups ranging in size from 2 individuals to as many as 38. The western populations have smaller group sizes, averaging 5 members, whereas eastern groups average 9.

The gorilla is found in two principal areas: equatorial West Africa and eastern Central Africa. The western lowland gorilla subspecies occurs in West Africa and is the most widespread. The recently identified Cross River gorilla, the rarest of the gorilla subspecies, is found on both sides of the Nigeria-Cameroon border. The eastern lowland gorilla subspecies occurs in the eastern portion of The Democratic Republic of the Congo. The mountain gorilla subspecies occurs in two populations, one on the extinct volcanoes of the Virunga Range along the borders of Rwanda, Uganda and The Democratic Republic of the Congo; and the other in the Bwindi (Impenetrable) Forest in southwest Uganda.

Hunting and forest clearance for agriculture and timber are the main threats. African lowland and montane forests are rapidly being destroyed to make way for food production uses such as cropping and livestock grazing. In addition, gorillas are killed in retaliation for crop-raiding. In Central Africa, commercial logging and petroleum exploitation are becoming an increasingly significant threat to the habitat of the gorilla. The internal trade in bushmeat, which occurs over much of the lowland gorillas' ranges, is now a threat. In recent years, human population pressures on the forest habitat of the eastern lowland gorilla have become worse due to the nearly 1 million refugees from nearby Rwanda and Burundi.

Tidbits

***  Gorilla commentary over the years:

- "Concealed among the thick branches of the forest trees, the gorilla, itself unseen, watches the approach of the unsuspecting native. Should he pass under the tree, woe betide him; for the gorilla lets down its terrible hind foot; grasps its victim round the throat, lifts him from the earth, and finally drops him on the ground, dead." (Wood 1860)

- "Many tales of its ferocity and strength are obviously untrue, but we think that too much has been disbelieved. That a huge arm descends from a tree, draws up and chokes the wayfarer, must be false, for intelligent natives have confessed to knowing no instance of the gorilla attacking man...  But we must believe that this ape, if provoked or wounded, is a terrible foe, capable of ripping open a man with one stroke of its paw, or of cracking the skull of a hunter as easily as a squirrel cracks a nut..." (Cornish 1906)

- "...recently a young child tumbled nearly 10 meters (33 ft) into a gorilla enclosure at the Brookfield Zoo in the USA. 'Onlookers screamed in horror' as a female gorilla, whose own infant clung to her back, shuffled over to the semi - conscious boy, cradled him in her arms, and carried the child to eagerly awaiting gatekeepers." (Kemf & Wilson 1997)

*** A smiling gorilla wears a "play face": his mouth is open, but his teeth and gums don't show.  His eyes are relaxed.  If his head and brow are drawn down, his lips pursed and slightly parted, and his eyes are staring at you, he's annoyed. (Wildl. Cons. 1999)

*** The mountain gorilla is especially susceptible to human diseases, as its genetic makeup is close to that of humans. Paradoxically, groups regularly visited by tourists have the highest rates of reproduction, and this may be because these groups are better protected from poachers than those not regularly visited. (Muruthi 2000)

***  In a study conducted in the Itombwe Massif in the The Democratic Republic of the Congo,  eastern lowland gorillas were observed in association with inhabited villages. At these sites, gorillas were often located in the immediate outskirts of settlements where they foraged in gardens and fallow fields. Based on reports of the villagers, the associations of gorillas with these settlements have been remarkably stable, in some cases persisting for over 60 years.  During surveys carried out in villages, over half the local villagers contacted  expressed ignorance of the protected status of gorillas. The potential danger, real or imagined, that gorillas living in the vicinity of villages posed to humans was the most frequently cited reason for killing them. (Omari 1999)

Status and Trends

IUCN Status:

  • 1970's - 1994: Vulnerable
  • 1996 - 2004: Endangered (Criteria: A2cd) (Same rating for G. beringei and G. gorilla) (IUCN 2004)

Countries Where the Gorilla Is Currently Found:

2004 (Gorilla beringei): Occurs in The Democratic Republic of the Congo (formerly Zaire), Rwanda, and Uganda. (IUCN 2004)

2004 (Gorilla gorilla): Occurs in Angola (Cabinda), Cameroon, Central African Republic, Equatorial Guinea, Gabon, Nigeria, and Republic of the Congo (formerly Congo). (IUCN 2004)

Taxonomy:

As of 2000, two species and four subspecies of gorilla are generally recognized:

  • Eastern Gorilla (Gorilla beringei)
    • Eastern Lowland Gorilla (Grauer's Gorilla) (Gorilla berengei graueri)
    • Mountain Gorilla (Gorilla berengei berengei)
  • Western Gorilla (Gorilla gorilla)
    • Cross River Gorilla (Gorilla gorilla diehli)
    • Western Lowland Gorilla (Gorilla gorilla gorilla)

A recent research project has gathered the first detailed evidence on the ecology of gorillas in the Nigeria-Cameroon border region, located more than 250 km (160 mi) north of the next closest population of gorillas. Early results from a small sample of DNA indicate large genetic differences between this population and other western gorillas. Such findings add to the results of measurements on the skulls of gorillas from the Nigeria-Cameroon border region, which support recognition of these animals as belonging to a distinct subspecies, Gorilla gorilla diehli (based on a name originally given to gorilla specimens from this area in 1904 by the German scientist Paul Matschie, who regarded them as a separate species). (Suter & Oates 2000)

A recent study of DNA indicated a striking divergence between the western lowland gorilla, on the one hand, and the eastern lowland and mountain gorillas, on the other hand, and raised the possibility that the western and eastern populations, which are separated by about 1000 km (620 mi), constitute separate species (Nowak 1999). The IUCN now recognizes this separation into two species (IUCN 2000).

Since the early 1980's, the gorillas of the Bwindi (Impenetrable) Forest of southwest Uganda were considered to be mountain gorillas, members of the same subspecies (Gorilla gorilla berengei; now Gorilla berengei berengei) as the population restricted to the six extinct volcanoes of the Virunga Range straddling the border of Rwanda, Uganda and The Democratic Republic of the Congo. Comparative study of DNA lends support to this classification. A recent study, however, indicates that the Bwindi gorillas are morphologically, ecologically, and behaviorally distinct from their Virunga neighbors, and suggests that they should not be classified as belonging to the mountain gorilla subspecies. Their taxonomy is as yet unclear. (Dieter Steklis et al. 1996/7, Kemf & Wilson 1997, Nowak 1999, McNeilage et al. 2001)

A population of gorillas in the vicinity of Mt. Kahuzi in The Democratic Republic of the Congo has sometimes been described as mountain gorillas (Gorilla gorilla berengei (now Gorilla berengei berengei)), but most agree that this population is actually a member of the eastern lowland gorilla subspecies (Gorilla gorilla graueri (now Gorilla berengei graueri)) (Nowak 1999).

Population Estimates:

[Note: Figures given are for wild populations only.]

WORLD 

    (Total of recent estimates listed below for each subspecies)

  • 1996 - 2000: Approximately 120,000 - 129,000 (200 or less Cross River gorillas; 8000 - 17,000 eastern lowland gorillas; about 600 mountain gorillas; more than 110,000 western lowland gorillas)
  • 2004: Approximately 98,000 (less than 300 Cross River gorillas; maybe less than 3000 eastern lowland gorillas; at least 700 mountain gorillas; 94,000 western lowland gorillas)

By Subspecies:

Notes:

  • Comparison of gorilla population estimates can be difficult, because early on there was lack of a clear distinction between the various subspecies, particularly between the eastern lowland gorilla (Gorilla gorilla graueri (now Gorilla berengei graueri)) and the mountain gorilla (Gorilla gorilla berengei (now Gorilla berengei berengei)), as well as between the different populations of the mountain gorilla.  
  • Estimates of the maximum population of the western lowland gorilla (G.g. gorilla) have increased substantially over the years, not because of an actual increase in numbers, but because much of their habitat had been unexplored and they have been discovered to occur in large areas of primary forest not previously known to contain them.

By Country:

History of Distribution:

The gorilla occurs in a range of tropical forest habitats. It is currently found in two principal areas: equatorial West Africa and eastern Central Africa. The western lowland gorilla subspecies occurs in West Africa and is the most widespread. The recently identified Cross River gorilla, the rarest of the gorilla subspecies, is separated into five isolated populations on both sides of the Nigeria-Cameroon border, more than 250 km (160 mi) north of the nearest population of western lowland gorillas. A gap of approximately 1,000 km (620 mi) exists between the western gorilla populations and the nearest populations of the eastern lowland gorilla subspecies, which occurs in 11 populations in the eastern portion of The Democratic Republic of the Congo. The mountain gorilla subspecies occurs in two populations: one on the extinct volcanoes of the Virunga Range along the borders of Rwanda, Uganda and The Democratic Republic of the Congo; and the other in the Bwindi (Impenetrable) Forest in southwest Uganda. (IUCN 2000a, Suter & Oates 2000, WWF/WCMC, Hall et al. 1998)

Distribution Map (13 Kb GIF) (Oates 1996, mapped by African Mammals Databank)
Distribution Map #2 (33 Kb JPEG) (iEARN Austral.)

Threats and Reasons for Decline:

Hunting and forest clearance for agriculture and timber are the main threats. African lowland and montane forests are rapidly being cut down to make way for food production uses such as cropping and livestock grazing. In addition, gorillas are killed in retaliation for crop-raiding. In Central Africa, commercial logging and petroleum extraction are becoming an increasingly significant threat to the habitat of the gorilla. The internal trade in bushmeat, which occurs over much of the lowland gorillas' ranges, is now a threat. In recent years, human population pressures on forest habitat of the eastern lowland gorilla have become worse due to the nearly 1 million refugees from neighboring Rwanda and Burundi. (Oates 1996, Kingdon 1997, WWF/WCMC, Hall et al. 1998)

Data on Biology and Ecology

Weight & Size:

Female gorillas weigh 70 - 140 kg (150 - 310 lb); males weigh 135 - 275 kg (300 - 600 lb) (Nowak 1999). Standing upright, the gorilla reaches a height of 1.25 - 1.75 m (4.1 - 5.75 ft) (WWF/WCMC).

Habitat:

Gorillas are forest-associated animals. Most gorillas inhabit lowland tropical rainforests and montane rainforests between 1500 - 3500 m (4900 - 11,500 ft). Different populations have exhibited preferences for forest margins, secondary forest (for example abandoned slash-and-burn patches, as well as recovering logging areas, where there is a dense tangle of ground-level herbaceous growth), swamp forests, bamboo forests and riverine forests. Recent studies have shown that western lowland gorillas make extensive use of primary forest, a fact that was not previously recognized. (Stuart & Stuart 1996, Kemf & Wilson 1997, Kingdon 1997, Nowak 1999)

The gorilla is one of the species that live in both the Guinean Forests of West Africa Biodiversity Hotspot (Cons. Intl. 2005) and in the Congolian Coastal Forests, Guinean Moist Forests, and Albertine Rift Highland Forests Global 200 Ecoregions. (Olson & Dinerstein 1998, Olson & Dinerstein 1999)

Age to Maturity:

Females become sexually mature at 7 - 8 years, but first mating usually occurs at about 10 years; males become sexually mature at 9 - 10 years, but first mating rarely occurs before 15 - 20 years (Stuart & Stuart 1996).

Gestation Period:

251 - 295 days.

Birth Season:

There is no evidence of a particular breeding season in the wild. 

Birth Rate:

Females give birth every 3.5 - 4.5 years (average 4 years, or 0.25 young/year). There is normally a single young, but twins occur rarely. Females generally give birth to only 2 - 3 surviving young during their reproductive life. (Fa et al. 1995, Nowak 1999)

Early Development:

Young gorillas are weaned at an age of  2.5 - 3 years (Stuart & Stuart 1996).

Dispersal:

The gorilla is an unusual social primate in that both males and females leave the natal group on reaching maturity. Departure usually seems to be of the female’s own volition, and she almost immediately joins with another group or a lone young silverback (an adult male, referred to as a "silverback" because of his coat coloring). The males remain solitary until they can attract females and establish their own groups. (Stuart & Stuart 1996, Nowak 1999)

Maximum Age:

Estimated at 35 years in the wild but may be up to 50 years. A captive lived for 54 years. (Stuart & Stuart 1996, Nowak 1999)

Diet:

The diets of the eastern and western gorilla populations differ considerably. Eastern animals are predominantly folivorous, but those in the west eat great quantities of fruit. Eastern gorillas feed primarily on leaves, shoots and stems (86% of the diet in one study). Galium vines, wild celery and three or four other species make up a high proportion of the diet. Small amounts of wood, roots, flowers, fruits, and grubs also are eaten. In the western populations, fruits are the most important element in the gorillas’ diet, although they also eat leaves, pith and stems (e.g. wild ginger). In a study undertaken on one western lowland gorilla group in Gabon, it was found that the fruits of at least 95 plant species were utilized. It was also found in Gabon that the gorilla frequently breaks into termite nests to feed on the insects inside. Western gorillas have also been observed wading through shallow pools and swamps to harvest water plants. They further differ from eastern animals in that they occasionally include some animal food in their diet. On the other hand, it has been observed that mountain gorillas had ample opportunity to eat eggs, helpless young birds, and the honey of stingless bees but never did. (Stuart & Stuart 1996, Kingdon 1997, Nowak 1999)

Gorillas rarely drink - they get their moisture from the plants they eat. (Wildl. Cons. 1999)

Behavior:

The gorilla is primarily terrestrial but is fully capable of climbing. Some have been observed feeding in trees at heights of 40 m (130 ft), and even a large male, weighing at least 200 kg (440 lb), frequently climbed to 20 m (65 ft). Contrary to general opinion, the gorilla is not afraid of water. Recent studies of the western lowland gorilla have shown that it is quite happy to wade around in swamp forests in search of edible aquatic plants. Gorillas are now known to wade freely through swamps and streams.  The gorilla is diurnal, with nearly all activity occurring between 0600 and 1800 hours. Gorillas spend most of their time foraging on the ground, although young animals and females, particularly lowland gorillas, frequently feed and sleep in trees. (Stuart & Stuart 1996, Nowak 1999)

Gorillas have a relaxed lifestyle, rising relatively late and feeding for about 2 hours in the morning and a further 3 - 4 hours in the afternoon, resting from about 1000 - 1400 hours. Before nightfall, they settle into their nests which are freshly constructed each night.  One study compiled a 24-hour activity budget (% of time) for the mountain gorilla: rest - 76.5 %, feed - 12.5 %, travel - 7.2 %, other - 3.8 %. Observations suggest that daily movement is usually about 400 - 1000 m  (1300 - 3300 ft). Some groups of mountain gorillas were observed to move 90 - 1800 m/day (300 - 5900 ft/day). Some observers have concluded that movements in the course of a year were not random but followed an established migratory pattern with respect to availability of food. (Schaller et al. 1985, Stuart & Stuart 1996, Nowak 1999)

Gorillas construct rough platforms, or nests, for sleeping at night or for rest during the day, either in a tree or on the ground. Every adult and weaned juvenile builds its own  nest. In some areas more than 90% of nests are made on the ground, but in other areas most nests are built in trees.  Adult males usually prefer the ground. Sleeping nests can be reliably distinguished from day nests or night nests where individuals did not sleep. A gorilla rarely takes more than a few minutes to make a nest, either standing or sitting in a central position, and pulling in the surrounding vegetation, which it tucks under and around itself. A nest is not used for more than a single night. Habitat type, group size and season all affect nest construction type. Variations in nests can include use of different species of plants and different construction techniques (e.g. branches broken rather than bent during nest construction).  (Simon & Geroudet 1970, Nowak 1999, Bermejo 1999, Remis 2000)

Social Organization:

Gorillas live in groups ranging in size from 2 individuals to as many as 38. The western populations have smaller group sizes, averaging 5 members, whereas eastern groups average 9. (Stuart & Stuart 1996) Some examples of group size estimates:

Mountain Gorilla:

  • Mean group size: 7.9 (early 1950's); 8.5 (1981) (Virunga population) (Aveling & Harcourt 1984).
  • Mean group size: 9.2 (1986) (Virunga population) (Aveling & Aveling 1989).
  • Mountain gorillas live in bisexual groups of 10 - 20 individuals, usually containing 1 silverback male, though groups with 2 or more silverbacks are not uncommon. Groups with more than 1 silverback can get quite large, numbering as many as 38 individuals, but groups of that size are less cohesive and likely to split into two groups. (Dieter Steklis et al. 1996/7)
  • Group size ranged from 2 - 30 individuals. On the average there were 16.9 animals. (Virunga population) (Schaller 1963, cited in Nowak 1999) In other regions average group size has varied from 6 - 13 (1977). (Nowak 1999)
  • Groups ranged in size from 2 - 23 individuals, with a mean of 9.8 (SD 6.2), or 10.2 after allowing for undetected infants (Bwindi population). Average group size in Bwindi is comparable with that in the Virungas. (McNeilage et al. 2001)

Western Lowland Gorilla:

  • Mean group size: 3.7 ± 3.1 weaned individuals (range 1 - 12) (Reserve de Faune du Dja, Cameroon) (Williamson & Usongo 1996)
  • Mean group size of 6.6 nests (range 1 - 26) [1 nest ~ 1 gorilla], and a median size of 7 nests in open-canopy forest and 3.5 nests in closed-canopy primary forest. (Odzala National Park, Republic of the Congo) Although large groups of gorillas (>26 individuals) are known from montane forests, this study is the first that observed such large groups in lowland tropical forests. (Bermejo 1999)
  • Mean group size: 4.7 (based on fresh and very recent nest-sites); median group size for all nest-sites: 4 (range among survey blocks 2 - 6). (Dzanga-Sangha Reserve, Central African Republic) (Remis 2000)

Gorillas do not defend a territory but remain in home ranges. There is no defense of the home range, and there is extensive overlap of the home ranges of groups. Aggressive interaction is usually avoided during encounters. (Stuart & Stuart 1996, Kingdon 1997)

If a gorilla group includes more than a single adult male, one is dominant and is the leader of the group, and only that one normally breeds. There is a general rank order for the group based mainly on size, with silverback males being dominant over all other animals. Groups are highly stable, and the dominant male retains leadership for years. Certain of the other males are only temporarily associated with the group and eventually leave to live alone or to join other groups.  Whenever established pairs are joined by other adult females, the sequence of arrival determines the female rank order. The mountain gorilla has less exclusive groups, with dominant silverback males tolerating a few younger adult males, and these larger groups attract more females. Mothers give continuous care and attention to their young, and the dominant male is always alert to the safety and well-being of all members of his group, willing to defend the young against all comers.  (Kingdon 1997, Nowak 1999)

Age and Gender Distribution:

Despite fluctuation in total numbers, the percent of immatures in one study of the Virunga population of mountain gorillas remained relatively stable - between 40 and 50%. (Dieter Steklis et al. 1996/7)

In another study of the Virunga population, on the average there were 16.9 individuals, including 1.7 fully adult males (silverbacks), 1.5 subadult males (blackbacks), 6.2 adult or subadult females, 2.9 juveniles (3 - 6 years old), and 4.6 infants (under 3 years old).  (Schaller 1963, cited in Nowak 1999)

In a study of the Bwindi population of mountain gorillas, of the 28 groups, 15 contained one silverback, whereas 8 had 2 silverbacks and 5 had 3 silverbacks, so that 46% of groups were multi-male. This is considerably higher than the figure of 29% in the most recent census of the Virunga mountain gorilla population, but comparable with earlier figures for the Virungas. The proportion of immature gorillas (i.e. infants plus juvenile and subadults) in the Bwindi population within groups was 37 %, which is comparable with that found in the Virunga population during the 1970's and early 1980's. (McNeilage et al. 2001)

Mortality and Survival:

Average probability of surviving per year from age of first reproduction to longevity: 0.91 (Slade et al. 1998)

Mortality in stable populations is 42% for immatures, mostly in the first year of life, and 5% for adults. (Nowak 1999)

Density and Range:

Density:

Eastern Lowland Gorilla (The Democratic Republic of the Congo):

  • 1.26 individuals/sq km (3.26 individuals/sq mi) (1998) (Cited in Remis 2000)
  • 3.7 individuals/sq km (9.6 individuals/sq mi) (mean of 11 high-density zones); 0.3 individuals/sq km (0.8 individuals/sq mi) (mean of 7 low-density zones) (Itombwe Massif) (Omari 1999)

Mountain Gorilla:

  • 0.73 individuals/sq km (1.9 individuals/sq mi) (early 1970's); 0.68 individuals/sq km (1.8 individuals/sq mi) (1981) (Virungas) (Aveling & Harcourt 1984)
  • 0.73 - 1.96 individuals/sq km (1.9 - 5.1 individuals/sq mi) (Virungas) (various studies) (Cited in Remis 2000)

Western Lowland Gorilla:

  • Cameroon:
    • 2.5 nesting individuals/sq km (6.5 nesting individuals/sq mi) (proposed Lobeke Forest Reserve) (1992)  (Cited in Usongo 1998)
    • Overall density of 1.71 weaned individuals/sq km (range: 1.02 - 2.86/sq km) (overall density of 4.42 weaned individuals/sq mi (range: 2.64 - 7.41 weaned individuals/sq mi)) and maximum density of 7.88 individuals/sq km (20.4 individuals/sq mi) (Reserve de Faune du Dja) (Williamson & Usongo 1996)
  • Central African Republic:
    • 0.89 - 1.45 individuals/sq km (2.31 - 3.76 individuals/sq mi) (reaching 5.6 individuals/sq km (14.5 individuals/sq mi) in light gaps and up to 10.96 individuals/sq km (28.4 individuals/sq mi) in secondary forest) (1988) (Cited in Williamson & Usongo 1996)
    • 1.6 individuals/sq km (4.1 individuals/sq mi) (1989) (Cited in Williamson & Usongo 1996)
    • 1.52 individuals/sq km (3.94 individuals/sq mi) (95% CI: 0.93 - 2.5 individuals/sq km (2.41 - 6.5 individuals/sq mi)). (Dzanga-Sangha Reserve) (Remis 2000)
  • Equatorial Guinea (Rio Muni):
  • Gabon:
    • 0.44 individuals/sq km (1.14 individuals/sq mi) (but up to 9.16 individuals/sq km (23.7 individuals/sq mi)); (1983) (Cited in Williamson & Usongo 1996)
  • Republic of the Congo:
    • 1.2 individuals/sq km (3.1 individuals/sq mi) in northern Republic of the Congo (2.4 individuals/sq km (6.2 individuals/sq mi) in swamp forest) (1992) to 2.6 individuals/sq km (6.7 individuals/sq mi) in the Likoula Swamp (1989) (Cited in Williamson & Usongo 1996)
    • 5.88 individuals/sq km (15.2 individuals/sq mi) in Raphia dominated swamp and 2.88 individuals/sq km (7.46 individuals/sq mi) in Raphia-Uapaca forest (Likoula Swamp) (Williamson & Usongo 1996)
    • 0.2 individuals/sq km (0.5 individuals/sq mi) (Motaba region) (Bowen-Jones & Pendry 1999)
    • 5.4 individuals/sq km (14.0 individuals/sq mi) (mean for the area). This area has the highest recorded densities of western lowland gorilla in Central Africa.  Gorilla densities were especially high in Marantaceae forest. The maximum density estimate of 11.3 nesting individuals/sq km (29.3 nesting individuals/sq mi) in Marantaceae forest in this study is the highest recorded for any vegetation surveyed. (Odzala National Park) (Bermejo 1999)

Range:

Home ranges vary from 5 - 35 sq km (2 - 14 sq mi). Those of western lowland gorillas are generally larger, primarily because of differences in diet. Some studies have shown that there are seasonal differences in range, based primarily on food availability and dietary preferences. (Stuart & Stuart 1996)

References

African Mammals Databank, Arkive, Aveling & Aveling 1989, Aveling & Harcourt 1984, Beamont 2004, Bermejo 1999, Blom et al. 1992, Bowen-Jones & Pendry 1999, Burton & Pearson 1987, Cons. Intl. 2005, Cornish 1906,  Cousins 1978, Dieter Steklis et al. 1996/7,  Fa et al. 1995, Focus 2004, Focus 2004b, Hall et al. 1998, Harcourt 1977, Harcourt et al. 1989, Harcourt & Groom 1972, iEARN Austral., IUCN, IUCN 1994, IUCN 1996, IUCN 2000, IUCN 2000a, IUCN 2003a, IUCN 2004, Kemf & Wilson 1997, Kingdon 1997, Macdonald 1984, McNeilage et al. 2001, Morland 1995, Muruthi 2000, National Zoo, Nowak 1999, Oates 1996, Omari 1999, Oryx 1979d, Plumptre 1998, Remis 2000, Schaller 1963, Schaller et al. 1985, Schaller 1995, Simon & Geroudet 1970, Slade et al. 1998, Stuart & Stuart 1996, Suter & Oates 2000, Usongo 1998, Vedder 1999, White 2002, Wildl. Cons. 1999, Williamson & Usongo 1996, Wilson 1984, Wood 1860, WWF/WCMC

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