Gorilla

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TAXONOMY

Suborder: Haplorrhini
Infraorder: Simiiformes
Superfamily: Hominoidea
Family: Hominidae
Genus: Gorilla
Species: G. beringei, G. gorilla
Subspecies: G. b. beringei, G. b. graueri, G. g. diehli, G. g. gorilla

Other names: gorilla (Finnish); gorille (French); gorilla (German); gorila (Spanish); bergsgorilla, gorilla, or låglandsgorilla (Swedish); G. gorilla: western gorilla; G.g. diehli: Cross River gorilla; G.g. gorilla: western lowland gorilla; G. beringei: eastern gorilla; G.b. beringei: Bwindi, mountain, or Virunga; G.b. graueri: eastern lowland gorilla or Grauer’s gorilla

Conservation status:
Critically endangered (G. gorilla), Endangered (G. beringei)

Life span: 30 to 40 years (wild), 50 years (captive)
Total population: approx. 130,000 (wild), 350 (captive)
Regions: Western and eastern central Africa
Gestation: 8.5 months (256 days)
Height: 1700 mm (M), 1500 mm (F)
Weight: 181 kg (M), 72 to 98 kg (F)

MORPHOLOGY

Western and eastern gorillas are more genetically distant from one another than are chimpanzees (Pan troglodytes) and bonobos (Pan paniscus) (Butynski 2001). There are few striking physical differences between subspecies of gorilla, though differences in dentition and craniometric analyses reveal distinguishing morphological characteristics of each subspecies (Rowe 1996; Leigh et al. 2003). To some extent, even the inexperienced observer can distinguish the subspecies from one another. Mountain gorillas have significantly longer hair than their conspecifics, while western gorillas have brown, not black, hair on their heads, and eastern gorillas have longer faces and broader chests than western gorillas (Rowe 1996; Nowak 1999). Gorillas have dark brown to black fur and black skin. Dominant adult males, called silverbacks, have a prominent sagittal crest and striking silver coloration from their shoulders to rump. Males and females are sexually dimorphic, with males weighing up to 181 kg (400 lb) in the wild and 227 kg (500 lb) in captivity and measuring, on average, 1700 mm, while females weigh between 72 and 98 kg (159 and 216 lb) and measure, on average, 1500 mm (4.92 ft) (Rowe 1996).

Gorilla
Gorilla

Spending the majority of their lives on the ground, the main locomotion pattern of gorillas is quadrupedal knuckle-walking although they do climb and spend limited amounts of time standing bipedally. Because of their sheer size, adult gorillas must climb near the main trunk of a tree or on large branches while juveniles and adolescents are more agile (Tutin et al. 1995; Rowe 1996).

Gorillas live between 30 and 40 years in the wild and up to 50 years in captivity (Stoinski pers. comm.).

RANGE

CURRENT RANGE MAPS (IUCN REDLIST):
Gorilla beringei | Gorilla gorilla

Gorillas are patchily distributed in east central and equatorial west Africa, separated by the Congo River and its tributaries. Western gorillas (including western lowland and Cross River gorillas) are found in a geographic area of about 709,000 km² (273,746 mi²) covering parts of Nigeria, Cameroon, Central African Republic (CAR), Equatorial Guinea, Gabon, Republic of Congo, Angola, and far-western Democratic Republic of Congo (DRC). Cross River gorillas are found in only a 750 km² (290 mi²) area in Nigeria and Cameroon, a pocket of land that is isolated from the majority of this region. Eastern gorillas (including mountain and eastern lowland gorillas) are found in portions of eastern DRC, Uganda, and Rwanda, in an area approximately 112,000 km² (43,243 mi²), though mountain gorillas are restricted to two locations, Virunga Volcanoes where the borders of Uganda, Rwanda, and DRC meet, and Bwindi-Impenetrable National Park, Uganda (Nowak 1999; Butynski 2001; Sarmiento 2003).

Population estimates based on nest counts, known areas of available habitat, and population density reveal startlingly low numbers for some subspecies: as high as 110,000 (G.g. gorilla), 250 to 300 (G.g. diehli), 17,000 (G.b. graueri), and 700 (G.b. beringei) (Butynski 2001; Plumptre et al. 2003; Stoinski pers. comm.). There are about 350 gorillas in zoos in the United States, all of them are western lowland gorillas (Goodall et al. 2003).

For more than 30 years, ongoing field research on the mountain gorillas has made them the most studied subspecies of gorilla. George Schaller conducted the first long-term research study on mountain gorillas starting in 1959. In 1967, notable researcher Dian Fossey spearheaded the Karisoke Research Center in the Virunga Volcanoes and since the inception of this field site, researchers have been unraveling the complexities of gorilla society, behavior, and ecology by studying habituated groups (it is one of the only study sites where gorillas are fully habituated). Another long-term study site is at the Lopé Reserve of Gabon, where Caroline Tutin and Michael Fernandez have been studying western lowland gorillas since 1984 (Doran & McNeilage 1997). Most of the information available about wild eastern lowland gorillas comes from studies in Kahuzi-Biega National Park in DRC (Tutin & Vedder 2001).

HABITAT

Because of their great geographical separation, about 750 km (466 mi), western and eastern gorillas live in dramatically different habitats (Tutin & Vedder 2001). Even within-species habitat variation is quite great, from swamp to montane forest. Eastern gorillas live in submontane and montane forests from 650 to 4000 m (2132 to 13,123 ft) (Butynski 2001; Sarmiento 2003). Mountain gorillas live at the highest elevations, from 2200 to 4000 m (7218 to 13,123 ft), in the Virunga Volcanoes while eastern lowland gorillas occupy submontane forests from 700 to 2900 m (2297 to 9514 ft) (Butynski 2001). Where mountain gorillas exist, there are two rainy and two dry seasons per year, with average rainfall of 2000 mm (6.56 ft) per year (McNeilage 2001). The rainy seasons are from March until May and September to November while the dry seasons are June through August and December through February (McNeilage 2001; Robbins & McNeilage 2003). Temperatures range between 3.9° C (39° F) and 14.5° C (58° F), though they may reach 25.8° C (78.44° F) (Sarmiento 2003). Eastern lowland gorillas live in primary and secondary forests in both highland and lowland forests across their range. They occupy montane, bamboo, and lowland forests at elevations of 600 to 3308 m (1969 to 10,853 ft) (Ilambu 2001). There are two rainy seasons, the first lasting from March to June and the shorter lasting from September to December. There are also two dry seasons, the longer from June to September and the shorter from December until March (Yamagiwa et al. 1996).

Gorilla
Gorilla

Western gorillas live in lowland, swamp, and montane forests from sea level to 1600 m (5249 ft) (Butynski 2001; Sarmiento 2003). As their common name implies, western lowland gorillas live in lowland and swamp forests at elevations up to 1600 m (5249 ft) while Cross River gorillas inhabit low-lying and submontane forests at elevations from 150 to 1600 m (492 to 5249 ft) (Sarmiento 2003). Western lowland gorillas that live in mixed swamp forests experience one rainy and one dry season per year. Average rainfall is 1526 mm (5.01 ft) with the greatest amount of rain falling between August and November and diminishing during December through March (Poulsen & Clark 2004).

ECOLOGY

The considerable dietary differences between mountain, western, and eastern lowland gorillas impact home range size and social behavior. Despite these differences, though, all gorilla groups exhibit synchronized activities and, throughout the day, alternate between rest periods and travel or feeding periods (Stewart 2001). Mountain gorillas are folivores, feeding on leaves, stems, pith, and shoots of terrestrial herbaceous vegetation. They preferentially choose high quality, high protein, low fiber, and low tannin foods from a small number of species and incorporate little fruit into their diets (McNeilage 2001). Where bamboo is available, it is usually favored and they spend much time digging to unearth tender shoots. Because they depend on a readily available, easily accessed food source, there is little competition for resources between groups, their home ranges are small, typically between three and 15 km² (1.16 and 5.79 mi²), and they move only 500 m (.311 mi) or less within a typical day (McNeilage 2001; Robbins & McNeilage 2003). Though they only utilize a few species in each habitat, mountain gorillas show wide dietary flexibility which enables them to occupy a wide variety of habitats within their range (McNeilage 2001).

Gorilla
Gorilla

The diet of eastern lowland gorillas is more diverse than the mountain gorillas’ and changes seasonally. While leaves and pith are staple parts of their diets, eastern lowland gorillas depend heavily on fruit (25 percent of their total diet), especially during the times of year when fruits are abundant. When they include insects in their diet, eastern lowland gorillas prefer ants (Yamagiwa et al. 1994). Eastern lowland gorillas generally use a small area for a few days and then travel long distances to another area. Eastern lowland gorillas that depend more heavily on fruit must travel farther in a day to find fruiting trees and have larger home ranges because of a relative scarcity of fruit. Their home ranges vary from 2.7 to 6.5 km² (1.04 to 2.51 mi²) while their day range is between 154 and 2280 m (.096 and 1.42 mi) (Yamagiwa et al. 1996).

Western lowland gorillas have little dependable access to high quality terrestrial herbs across their range, but some areas are rich in aquatic herbs and they do eat herbaceous vegetation. Fruit is widely available, though dispersed, across their range, and is a central component of their diet, especially during times of fruit abundance (Tutin 1996; Doran & McNeilage 2001; Doran et al. 2002). Termites and ants are also important dietary staples. Western lowland gorillas have the largest home ranges and travel the farthest of all gorilla subspecies because of their reliance on fruit. The average distance traveled per day is 1105 m (.687 mi) and western lowland gorillas range over seven to 14 km² (2.70 to 5.41 mi²) (Tutin 1996).

In some parts of their ranges, gorillas are sympatric with chimpanzees (Pan troglodytes) and dietary overlap in plant food and fruit is great. Where they occur together, gorillas and chimpanzees also have similar habitat use patterns and ecological competition is likely to occur (Kuroda et al. 1996). Though they share a similar niche, competition has not been recorded at any of the sites where the two apes overlap (McNeilage 2001).

Gorillas are vulnerable to predation by leopards (Panthera pardus), though direct documentation of attacks is difficult to obtain and rare. Evidence from leopard scat in areas where gorillas range is often the only means of confirming leopard predation, though even this is questionable as the large cats could simply be scavenging carcasses (Fay et al. 1995).

Content last modified: October 4, 2005

Written by Kristina Cawthon Lang. Reviewed by Tara Stoinski.

Cite this page as:
Cawthon Lang KA. 2005 October 4. Primate Factsheets: Gorilla (Gorilla) Taxonomy, Morphology, & Ecology . <http://pin.primate.wisc.edu/factsheets/entry/gorilla/taxon>. Accessed 2020 July 22

SOCIAL ORGANIZATION AND BEHAVIOR

Current knowledge on the social organization and behavior of gorillas is dominated by results from research on mountain gorillas though there are some data for eastern and western lowland gorillas. The minimum group size for all subspecies is two individuals (usually a silverback and a female), except for males ranging alone, while maximum group size varies slightly for each subspecies (Yamagiwa et al. 2003). The maximum group size for mountain gorillas can exceed 20 individuals, while eastern and western lowland gorillas generally are not found in groups larger than 17 to 20 individuals and western lowland gorilla groups are always observed in groups smaller than 20 individuals (Yamagiwa et al. 2003).

Gorilla
Gorilla

Mountain gorillas live in age-graded groups of, on average, 9.2 individuals, with one adult male (though there may be more than one), multiple adult females, and their offspring (Watts 1996; Doran & McNeilage 1997; Robbins 2001). Natal dispersal is much more common for females than for males in mountain gorillas (Watts 1996). In general, females emigrate from their natal groups to avoid inbreeding. They do not always stay in their new groups throughout their lives and secondary transfer is common (Watts 1996; Robbins 2001). Males either remain in their natal groups or disperse. If young males remain in their natal groups, they will be subordinates to the silverback, but may have the opportunity to mate with new females or become dominant if the silverback dies. The other strategy for mountain gorilla males is to leave their natal groups and become solitary, attracting emigrating females and starting new social groups. In groups containing only one silverback male, females disperse and find new social groups upon the death of the silverback (Yamagiwa & Kahekwa 2001). This may be related to high rates of infanticide documented among mountain gorillas at Karisoke. Infants deprived of protection by an adult male are almost certain to be killed and as a tactic to protect against this, females join new groups in the absence of a silverback (Watts 1989). Until recently, infanticide had only been recorded among mountain gorillas; direct evidence now exists for eastern lowland gorillas and indirect evidence has been recorded among western lowland gorillas (Stokes et al. 2003; Stoinski pers. comm.). Finally, males can live in all-male groups, although this seems to be a strategy generally employed by young males when their group disintegrates before they reach adulthood (Stoinski pers. comm.).

Gorilla
Gorilla

Eastern lowland gorillas generally live in groups of one male, multiple females, and their offspring, though these can shift to multi-male groups for brief periods (Yamagiwa et al. 2003). The average group size is 9.8 individuals (Yamagiwa & Kahekwa 2001). Males spend a few months to a few years alone after emigrating from their natal groups at or before the age of 15, eventually attracting dispersing females and creating a new social group (Yamagiwa et al. 2003). Average age of transfer for female eastern lowland gorillas is nine (Yamagiwa & Kahekwa 2001; Yamagiwa et al. 2003). Female gorillas do not always emigrate independently; sometimes they transfer with another female to join a solitary male. Group succession, as seen in male mountain gorillas that remain in their natal groups, has not been observed in eastern lowland gorillas. If the silverback dies, the multi-female group and their offspring may continue to associate, rather than disperse, until a maturing silverback transfers into the group (Yamagiwa & Kahekwa 2001). One possible explanation for this behavior is protection against predators. Rather than roaming with just their offspring, females remain in groups of unrelated individuals to decrease chance of being attacked by leopards (Yamagiwa & Kahekwa 2001).

Difficulties with habituation and ecological constraints on observation have limited the research on social behavior of western lowland gorillas (Magliocca et al. 1999; Parnell 2002; Stokes et al. 2003). Group composition in western lowland gorillas is generally one silverback, multiple females, and their offspring with groups averaging 8.4 individuals (Parnell 2002). Groups with two silverbacks have been observed at several sites (Stoinski pers. comm.). Males generally emigrate from their natal groups and are solitary, as is seen in eastern lowland gorillas. Western lowland gorillas were not thought to live in bachelor groups btu there is now evidence from several sites that males will coexist without breeding females; group composition generally consists of a single adult male plus several younger males and nonreproductive females (Stoinski pers. comm.). Both natal and secondary transfers are observed in female western lowland gorillas and, as is seen in mountain gorillas, when the silverback dies, groups disband and females immigrate into new groups (Stokes et al. 2003). Though it has never been directly observed among western lowland gorillas, infanticide is the probable cause of this behavior. Females protect against infanticide when their resident silverbacks die by seeking the protection of other adult males in new groups (Stokes et al. 2003).

Knowledge about social relationships is most extensive for mountain gorillas. The core of social groups is the male-female bond, which is reinforced by grooming and close proximity (Watts 2003). It is important for female mountain gorillas to develop strong relationships with males because males offer such services as protection against predators, protection against infanticide by other males, and mating opportunities (Watts 2001). It is common to see aggressive behavior between males and females, though rarely is it intense or does it lead to serious injury (Watts 1996). Female-female relationships vary, but generally differentiate along lines of relatedness; maternal relatives associate closely and often affably interact. Generally, though, female gorillas have limited friendly relationships and multiple aggressive encounters (Watts 1996). These aggressive encounters often revolve around social access to males, and males intervene in contests between females (Watts 2003). Relationships between male gorillas are generally weak, especially in heterosexual groups where the dominance hierarchy is quite apparent and there is strong competition for mates. Relationships between members of all-male groups, in those subspecies where they occur, are slightly more affiliative, and they socialize through play, grooming, and close proximity (Robbins 2001).

REPRODUCTION

Gorilla mother and infant
Gorilla

Data from wild mountain gorillas and captive western lowland gorillas provide the majority of information about reproductive parameters of gorillas and the differences between the subspecies are few. Menarche occurs in female gorillas around age six and is followed by a period of adolescent infertility that usually lasts two years (Czekala & Robbins 2001). The estrus cycle lasts between 30 and 33 days and there are very subtle outward signs of ovulation, unlike the very obvious sexual swellings seen in chimpanzees (Pan troglodytes) and bonobos (P. paniscus). Gestation lasts 8.5 months. For wild mountain gorillas, the average age at first parturition is 10 years and the interbirth interval is four years (Czekala & Robbins 2001). It is more difficult to assess male reproductive maturity because they can be fertile before exhibiting secondary sexual characteristics (the silver saddle that characterizes adult males). Males between eight and 12 years are called blackbacks (Robbins 2001). In captivity, though, males can sire offspring by the age of six (Stoinski pers. comm.). Usually by age 12 or 13, males can be considered silverbacks, but most will not reach their full adult size until the age of 15 (Czekala & Robbins 2001).

There is no evidence of birth seasonality and mating occurs year-round (Watts 1991; 1998). A female will initiate copulation by pursing their lips and slowly approaching a male, establishing prolonged eye contact. If he does not respond she may reach towards him, touch him, or slap the ground in front of her to attract his attention (Sicotte 2001). In groups with multiple males, solicitation is taken as indication of female preference, though females may be coerced to mate with multiple males during the estrus period (Sicotte 2001). A male initiates copulations by approaching the female and displaying at her or touching her and giving a “train grunt” vocalization (Watts 1991).

PARENTAL CARE

Since mortality is as high as 38% in mountain gorillas during the infancy period (from birth to three years), caregivers, primarily females, are acutely important in the survival of their infants (Watts 1989). Because of their long period of development and dependence, gorilla mothers can expect to invest years caring for their vulnerable offspring. Although male gorillas do not take an active role in caring for infants, they play an important role in their socialization, often associating with older infants and juveniles (Stewart 2001). The relationship that develops between the silverback and infants in his group is usually supportive; he serves as an attachment figure during the difficult time of weaning and he shields young gorillas from intragroup aggression by intervening in disputes involving older, more dominant individuals (Stewart 2001).

Gorilla mother and infant
Gorilla

For the first five months of life, infant mountain gorillas remain in constant contact with their mothers and females seek close proximity to their resident silverback for protection (Stewart 2001). During this period, infants are dependent on their mothers for food, suckling at least once per hour, and sleep at night in their mothers’ nests (Stewart 1988). After five months, mother-infant pairs break body contact, but only for a few seconds and by 12 months, infants venture up to, but never more than, five meters (16.4 ft) away from their mothers. By 18 to 21 months, this distance between the pair is regular and increases (Fletcher 2001). Concurrent with this decrease in proximity is a decrease in nursing frequency, with infants only nursing once every two hours (Stewart 1988). By the age of 30 months, infants spend only half of their time with their mothers.

The juvenile period is from three to six years and is characterized by a decrease in maternal grooming, no longer sharing a sleeping nest with the mother, and weaning (Stewart 2001). Because of the enormity of the task of rearing infants and the stress of lactation on the mother’s body, female gorillas experience lactational amenorrhea until the infant is weaned at three or four years. After the infant is weaned, the mother begins to ovulate and shortly thereafter becomes pregnant (Stewart 1988; 2001). Weaning conflict is minimized in gorillas, compared to other great apes, because of the cohesive nature of gorilla groups. The constant availability of play partners (including the silverback) may contribute to less intense conflict between mother and infant during this period (Fletcher 2001).

COMMUNICATION

Vocal communication among gorillas is important in within-group interactions as well as extra-group interactions. Within-group calls, include “copulatory grunts” and “whimpers” during copulation, “whines” and “whimpers” by infants, “play chuckles” during play, “intense” and “mild cough grunts” during mild threat displays, and “close” calls that include both “syllabled” and “non-syllabled” calls such as “train-grunts” and “dog whines” (Fossey 1972; Harcourt et al. 1993). “Close” calls are commonly given within the group in situations of either potential separation or potential conflict. Extra-group calls serve to alert group members of potential predation and include “barks” or are given as long-distance threat displays upon detection of another group and include the “hoot series,” which may be accompanied by chest beating (Fossey 1972; Harcourt et al. 1993). Most calling occurs within-groups during feeding times, though gorillas also call during rest periods as well (Harcourt et al. 1993).

LISTEN TO VOCALIZATIONS

The communicative abilities of gorillas have also been studied in captivity, and one gorilla in particular, has been the focus of studies trying to understand language acquisition in humans. For over 30 years Francine Patterson has worked with Koko, a western lowland gorilla, teaching her American Sign Language and English. Today Koko can use over 500 signs and understand spoken English, though the physiological differences between apes and humans make it impossible for her to speak (Patterson & Gordon 2001).

Content last modified: October 4, 2005

Written by Kristina Cawthon Lang. Reviewed by Tara Stoinski.

Cite this page as:
Cawthon Lang KA. 2005 October 4. Primate Factsheets: Gorilla (Gorilla) Behavior . <http://pin.primate.wisc.edu/factsheets/entry/gorilla/behav>. Accessed 2020 July 22.

INTERNATIONAL STATUS

CITES: Appendix I (What is CITES?)
IUCN Red List: G. gorilla: CR; G. beringei: EN (What is Red List?)
Key: CR = Critically endangered, EN = Endangered
(Click on species name to see IUCN Red List entry, including detailed status assessment information.)

Gorilla Silverback
Gorilla

All gorillas face a very high risk of extinction in the wild in the near future if current threats do not subside. Hunting, forest clearance for agriculture and timber, and disease are the main threats to gorilla survival and these problems continue to increase in intensity and extent. Gorillas, like many African primates, are also subject to human warfare in parts of their range.

CONSERVATION THREATS & POTENTIAL SOLUTIONS

Threat: Human Induced Habitat Loss and Degradation

Habitat loss and modification due to human activity is a primary threat to gorilla survival. Agriculture, logging, fuelwood and forest product collection, and grazing domestic animals all degrade gorilla habitat and are problems that only increase as the human population in Africa grows (Plumptre et al. 2003). Only about 20% of gorillas live inside protected areas where, in theory, they are safe from habitat modification by encroaching humans. The remaining 80% are severely threatened by human induced habitat modification (Harcourt 2003). Mountain gorillas, while numbering only a few hundred, live in well-protected national parks known as the Virunga Conservation Area comprised of Parc National des Virunga, Parc National des Volcans, and Mgahinga Gorilla National Park (Steklis & Gerald-Steklis 2001). Habitat destruction has subsided in this area in recent years (Tutin & Vedder 2001; Plumptre et al. 2003). The growing human population on all sides of the mountain gorillas’ habitat allows for little buffer between the apes, and human activities like cattle grazing and collection of forest products have been problematic in the past and may become so in the future if political instability results in another civil war (Oates 1995; Steklis & Gerald-Steklis 2001).

Eastern lowland gorillas living in war-torn DRC are losing habitat faster than any other gorilla population (Plumptre et al. 2003). Logging, agriculture, and livestock grazing are all important economic activities for humans that lead to habitat modification in the eastern lowland gorilla’s range. Lowland populations are being forced into higher altitudes where steep slopes are not conducive to farming or ranching, isolating the population even further (Ilambu 2001). Following wars in 1996 and 1998-99, a huge influx of refugees from Rwanda compounded the problem as more pressure was put on the forest for fuelwood and food collection. The potential far-reaching effects of this sudden increase in human population will not be known for some time (Ilambu 2001; Tutin & Vedder 2001). Mining prospects in DRC are also having devastating effects on the habitat and gorilla population (Stoinski pers. comm.). Ecotourism can be a positive, revenue-earning undertaking for some communities, but when poorly managed can have negative impact on the animals or ecosystems it has been implemented to save. In the case of eastern lowland gorillas, ecotourism has had a negative impact on the gorillas and their habitat. Implemented as a source of revenue for local communities, the large groups of frequent visitors severely impacted high-altitude vegetation and were disturbing to the gorillas (Tutin & Vedder 2001).

The majority of western gorillas live outside protected areas and are therefore most at threat from human induced habitat modification. Fortunately, though, where gorillas exist in the remote forests of the Congo Basin, they are not subject to human disturbance. Interestingly, though, gorillas can coexist with logging because they tend to favor the areas of secondary vegetation that grow after an area has been clear cut (White & Tutin 2001; Plumptre et al. 2003). Unfortunately, with logging comes habit fragmentation by logging roads and easy access by hunters. Forest products are in increasing demand in some parts of their range where human populations are high and continuing to grow, including Nigeria (Cross River gorilla), southern Congo, and parts of Equatorial Guinea (Tutin & Vedder 2001).

Potential Solutions

Great strides have been made in reversing the population decline of mountain gorillas. With the support of notable gorilla researcher Dian Fossey, the Mountain Gorilla Project was launched in Rwanda in 1979 and included multiple approaches to conservation including education, ecotourism, and patrols to keep people and cattle out of the protected habitat (Steklis & Gerald-Steklis 2001; Tutin & Vedder 2001). While the Mountain Gorilla Project became the International Gorilla Conservation Program and continues its work today, many other organizations have been involved in similar programs aimed at educating local people, mountain gorialls have become a source of regional and national pride in Rwanda (Tutin & Vedder 2001).

More security is needed surrounding the Kahuzi-Biega National Park, where eastern lowland gorillas are studied (Tutin & Vedder 2001). Though ecotourism was successful at this site at one time, poor management led to the disturbance of the gorilla population and the destruction of habitat. Because the interest still exists and it is quite a lucrative undertaking, well-managed ecotourism operations focusing on small groups of visitors at infrequent intervals may revive the local economy of this area of DRC. Unfortunately, political instability in the region may prevent this option currently, and some effort should be made to secure the region from encroachment of human populations that extract forest resources, by using guards and continued presence of researchers. Columbotantalite (also called Coltan) reserves scattered throughout DRC have also drawn thousands of people into gorilla habitat, affecting the gorilla populations. An ore used to make semiconductors for electronics, including cell phones and computers, in the late 1990s coltan was sold for US$80 per kilogram and was an attractive prospect for people who made less than US$30 per month (Plumptre et al. 2003). Unfortunately, huge reserves of this ore are found in Kahuzi-Biega National Park and thousands of settlers in mining camps severely affected the local population of eastern lowland gorillas.

Western lowland gorillas that occupy swamp habitats that are unsuitable for commercial logging and are difficult to access by local people trying to extract forest products during the rainy season should be the focus of conservation activities. These areas have high population densities of gorillas and should be protected from future human incursion (Tutin & Vedder 2001). Though it is a difficult task to convince people to protect a population that is not currently severely at risk, it must be emphasized that these populations are healthy and will remain that way only if they are unharmed by habitat destruction in pristine forests (Tutin & Vedder 2001). Where western lowland gorillas are threatened by agriculture and selective logging (southern Republic of Congo and Equatorial Guinea), efforts should be made to establish protected areas in congruence with active field research sites. The major parks that have been established in western lowland gorilla range include Dzanga-Sangha National Park in CAR and Nouablale-Ndoki National Park in Congo (Tutin & Vedder 2001). Another key area that has not attained protected status is Lopé Faunal Reserve in Gabon where researchers have worked hard to habituate the gorillas.


Threat: Invasive Alien Species

Gorillas are highly susceptible to human diseases, and where they are immunologically naïve, the influx of poachers, soldiers, local communities, and domestic animals facilitates the spread of pathogens in small communities (Mudakikwa et al. 2001; Plumptre et al. 2003). Gorillas in Republic of Congo and Gabon are currently threatened by an epidemic of Ebola hemorrhagic fever. Even in the most remote areas of their region, western gorilla populations have declined in congruence with human outbreaks of the disease and carcasses found have tested positive for Ebola (Walsh et al. 2003).

Some other examples of zoonotic transfer include an epidemic of scabies, or sarcoptic mange, documented among a group of mountain gorillas in Bwindi Impenetrable National Park, the entire group was infected and it resulted in the death of an infant while respiratory illness claimed the lives of six mountain gorillas in the Virunga Volcanoes in 1988 (Wallis & Lee 1999). In the Virunga Conservation Area, emergency medicine and preventative health monitoring has been conducted by the Mountain Gorilla Veterinary Project since 1985 (Mudakikwa et al. 2001). The major groups that pose unique disease risk for mountain gorillas include local people, conservation personnel, and ecotourists (Mudakikwa et al. 2001). Though contact between gorillas and local people is limited to when they enter the park illegally or when gorillas leave the park boundaries and raid crops, this is significant enough to spread disease to the vulnerable gorillas including scabies, respiratory tract infections, intestinal parasites, skin disorders, and measles (Mudakikwa et al. 2001). Diseases are also transferred between park staff and tourists and gorillas as well, and while precautions are taken, this still poses a threat to the health of mountain gorillas.

Potential solutions

Educating local communities about zoonotic diseases may decrease disease transfer, and ideally, providing more widespread access to health care would also be useful. Where gorillas come in contact with researchers, park visitors, and staff, implementing even stronger protocol that includes face masks, gloves, required immunization, and further required distances from the animals may also decrease chances of disease transfer (Butynski 2001). Currently, field personnel working with the research populations of mountain gorillas take part in an employee health program designed to limit disease transfer to gorillas (Stoinski pers. comm.). In populations as small as the mountain and Cross River gorilla’s, it is imperative to minimize the possibility of infectious disease transfer as this could eliminate both populations entirely.

Research on vectors of and vaccines for the Ebola virus are necessary to alleviate both human and ape suffering in regions where outbreaks occur (Walsh et al. 2003). Coupled with epidemiological research, law enforcement is necessary to prohibit contact between humans and apes, especially in targeted regions. This includes forecasting disease movement (among both humans and gorillas), anticipating where the next outbreak is likely to occur, and implementing strict policies and effective law enforcement measures to isolate potential outbreaks.


Threat: Harvesting (hunting/gathering)

More threatening than habitat loss in some areas, hunting of gorillas for meat as well as capture of animals for collections are other hazards greatly affecting gorilla populations across Africa. Where human populations encroach on gorilla habitat and forest products such as fuelwood and timber are sought, poaching is generally also a problem, either for food or for sale (Plumptre et al. 2003).

Mountain gorillas in the Virunga Conservation Area are heavily protected and although poaching had been reduced to zero), the past few years has seen a resurgence in poaching for infants for the pet trade (Stoinski pers. comm.).

People living in the range of eastern lowland gorillas have traditionally had taboos against eating gorillas, though these customs are being quickly replaced. Civil war in DRC has led to mass hunger in the area as well and more often eastern lowland gorillas are being eaten for subsistence (Plumptre et al. 2003). Mining coltan in Kahuzi-Biega National Park has also led to drastic declines in gorilla populations, not simply because of habitat disturbance, but because of subsistence hunting by the thousands living in mining camps (Plumptre et al. 2003). Insecurity in the region prevents guards from stopping this influx of people and hunting will likely continue if the price of coltan increases in the future.

Western gorillas that live in areas where logging activity is ever-increasing are also subject to hunting. Logging and the bushmeat market are inextricably linked and unfortunately, the social structure of western lowland gorillas makes them particularly susceptible to devastation by only a few hunters (Tutin & Vedder 2001). Entire groups of western lowland gorillas can be wiped out by a single or a few poachers. The silverback in a group will approach and display against any perceived threat, including poachers, and in doing so, he is an easy target and is quickly killed. Poachers will capture the infants for sale as pets, often killing the mother that is defending her infant (Tutin & Vedder 2001). Moreover, poachers are able to reach the dense, most remote areas of forests as logging companies establish roads and transportation from small towns and cities is available deep into the forests (Butynski 2001; Plumptre et al. 2003). Company employees living in small logging towns are able to afford meat, and it is often less expensive to purchase bushmeat than other sources of protein. Almost all facets of the bushmeat trade are controlled or facilitated by logging companies: they sell guns and ammunition, provide cable for snares, transport poachers into the forests on trucks, carry the meat out on trucks, employees purchase it in town, and boats and trucks transport the meat to larger markets in cities (Butynski 2001; Wilkie & Carpenter 2001).

Potential solutions

Economic value must be given to live gorillas if local communities are to stop pursuing them for meat. Alternately, world aid and development organizations must give fiscal incentives for gorilla-friendly development projects that include alternate protein sources. Education of local communities or stakeholders is also necessary if the bushmeat trade is to subside. Including stakeholders in research at field stations, guard duties, or education programs are all ways of providing economic opportunities and incentives for protecting gorillas as well as creating a bond between people and apes.

Foreign logging companies must also be held accountable by the global community for their role in the bushmeat trade. Boycotts of tropical hardwoods in developed countries that purchase lumber from these companies or cancellation of logging concessions in countries where companies are actively involved in transporting bushmeat could help (Butynski 2001). Furthermore, gorilla-friendly certification programs by independent consultants could validate the practices of logging companies and provide an alternative to western consumers that are interested in tropical wood (Butynski 2001).

In situ refuges and sanctuaries for orphan gorillas confiscated from markets play an important role in assisting law enforcement and as education centers for local people.


Threat: Accidental Mortality

The bushmeat market targets more animals than primates, snares and traps are set for duikers, pigs, and rodents as well (Mudakikwa et al. 2001; Wilkie & Carpenter 2001). Unfortunately, snares are frequent causes of human-induced injuries to gorillas and can lead to loss of limbs or severely painful deaths if not treated (Mudakikwa et al. 2001). Gorillas that are caught in snares struggle to free themselves and are often cut on their limbs, hands, and feet; if these cuts become infected, without proper medical attention, the gorilla may likely die (Mudakikwa et al. 2001; Plumptre et al. 2003).

Potential solutions

Even with vigilant patrolling, snare removal is a constant challenge in areas where gorillas are sympatric with desirable animals (Hall et al. 1998; Plumptre et al. 2003). Mountain gorillas that encounter snares and are injured by them are treated by emergency medical staff of the Mountain Gorilla Veterinary Project. This process greatly decreases the chances of amputation and secondary bacterial infection. As the snare is removed, the wounds are cleaned and treated, and the injured animal is monitored to assess if follow up care is needed (Mudakikwa et al. 2003). Though there are great challenges and risks in undertaking this type of treatment for wild gorillas, it is a possibility for similarly habituated populations and has greatly reduced mortality caused by snare wounds among mountain gorillas. Snare patrols by researchers and field assistants coupled with intervention upon injury may decrease accidental mortality in gorillas.


Threat: Persecution

Large and imposing, gorillas are often perceived as dangerous by most humans who share their range and their image is not helped when they periodically raid plantations in some areas (Hart & Hall 1996; Tutin & Vedder 2001). Furthermore, gorillas that attack and seriously injure farmers on land adjacent to parks are even more despised and targets for retaliation (Butynski 2001).

Potential solutions

Public education programs about gorillas may increase tolerance for them in local communities that come in contact with them on farms and plantations. Teaching members of the community about the uniqueness of gorillas and the ecosystem services they provide coupled with compensation for injuries or crops that are lost or damaged may improve gorilla-human relationships in some areas.


Threat: Natural Disasters

Cross River gorillas live in a tiny fragment of forest in Nigeria and Cameroon where the dry season is long and the forest is susceptible to destructive fires. Fires started outside their range by local farmers, hunters, and pastoralists can get out of control and sweep through the dry forest, causing significant damage (Oates et al. 2003).

Potential solutions

Discouraging fire as a tool to clear land during this season is one approach to decrease the chance of forest fires. Limiting burning to certain times of year when the forest is not as vulnerable is another option to avoid devastating fires.


Threat: Changes in Native Species Dynamics

Though gorillas and chimpanzees have overlapping ranges at multiple sites throughout Africa, the two apes do not compete for access to resources, in fact, they actively avoid competition by exploiting different niches during different times of year (Kuroda et al. 1996; Yamagiwa et al. 1996).

The effect of leopard predation on gorilla populations is negligible (Fay et al. 1995).


Threat: Intrinsic Factors

Long interbirth intervals and high infant mortality make reproduction a slow process for all subspecies of gorillas. While these intrinsic factors do not limit population growth by themselves, when disrupted by disease, abnormally high infant mortality, stress from disturbance, and other environmental hazards, recruitment may dwindle (Butynski 2001; Tutin & Vedder 2001).

Higher mortality during the rainy season has been documented among mountain gorillas. Low temperatures coupled with heavy rainfall lead to conductive heat loss and respiratory infections (Watts 1998).

Severely isolated populations of gorillas are threatened by the effects of limited gene flow, restricted range, and low densities. Small populations are at risk of inbreeding depression, are vulnerable to stochastic events, and genetic fixation of deleterious alleles is possible (Oates et al. 2003).

Potential solutions

The establishment of well-funded, well-run national parks is essential to gorilla conservation. Given the challenges of protecting habitat in countries ravaged by civil war, where human populations often live in substandard conditions, with few if any government services, and law enforcement is limited, the international community will have to support conservation efforts (Plumptre et al. 2003). Integrated conservation and development programs may be useful tools in areas where human suffering leads to loss of biodiversity and international aid organizations must be willing to create projects that provide opportunities for people without sacrificing the integrity of conservation goals.

Maintaining corridors of habitat between fragments of forest in which the least numerate subspecies exist as well as strict protection of these areas from poachers and encroachment by human populations will help bolster gene flow (Oates et al. 2003).


Threat: Human Disturbance

War and civil unrest are indisputable causes of loss of biodiversity in Africa. Well armed insurgents seek refuge in forests, move between borders, set up camps and kill gorillas for subsistence usage or sport. Moreover, masses of displaced people seek food and shelter as they flee from violent conflict. This has resulted in large tracts of land being cleared for fuelwood, hunting of gorillas for food, and transmission of disease between humans and gorillas. While the extent of the damage following conflict is largely unknown, there are undoubtedly negative impacts on all subspecies of gorillas (Vedder et al. 2001; Plumptre et al. 2003).

Potential solutions

By looking at historical patterns of warfare and civil unrest, much can be learned about potential future threats to gorillas. For example, parks and reserves on country borders are extremely susceptible to becoming zones of military operations, park staff and their families are at very high risk if they remain to carry on their duties, and international monetary support is likely to dissipate as conflict heightens (Vedder et al. 2001). There are some positive lessons learned as well, though. Where ecotourist activities are important, less damage is likely to occur, in areas of long-term research and commitment, fewer losses are incurred, and the support and commitment of junior staff should not be underestimated (Vedder et al. 2001). While there are seemingly few solutions to the deep-rooted tensions in the region, conservationists should remain hopeful that the capacity for recovery, of both people and wildlife, is great and cannot be underestimated.

LINKS TO MORE ABOUT CONSERVATION

CONSERVATION INFORMATION

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Content last modified: October 4, 2005

Written by Kristina Cawthon Lang. Reviewed by Tara Stoinski.

Cite this page as:
Cawthon Lang KA. 2005 October 4. Primate Factsheets: Gorilla (Gorilla) Conservation . <http://pin.primate.wisc.edu/factsheets/entry/gorilla/cons>. Accessed 2020 July 22.

 

 

 

The following references were used in the writing of this factsheet. To find current references for Gorilla, search PrimateLit.

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Gorilla artwork
Gorilla

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Content last modified: October 4, 2005

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