Limber 512 Gorilla video notes (rev 02/06/12)

Limber 512 Gorilla video notes p. 1

1 Gorilla

There are three distinct subspecies: Mountain and eastern and western, lowland gorilla.

A. Mountain gorilla

Discovered in 1902, the mountain gorilla is a rare endangered species, estimated population is less than 700. Fossey (1983) counted 242; less than half reported 20- years earlier by Schaller (1964). There have been some recent gains. The Mountain Gorilla --naturally--lives at higher altitudes, is more terrestrial, has longer hair and expanded nostrils than the lowland varieties.
Fossey reports 29 morphological differences. These animals have been even more threatened by recent civil wars in Rwanda and nearby countries. See Weber & Vedder (2001) notes below and Google for recent problems.

Here is a recent (2012) report on the Bwindi National Park, Uganda where maybe 1/2-1/3 of all mountain gorillas live. Compare populations of these gorillas observed in the Virunga National Park. They eat somwhat different diets and display different behaviors, eg. even Bwindi silverbacks may climb for food.

B. lowland gorillas

Until recent ebola epidemics it was estimated there were up to 10,000 of these animals. The nose of these animals forms a continuous heart-shaped ridge around the nostrils. Their climate is warmer; their diet may contain more fruit. These are the gorillas seen in zoos. The eastern and western varieties may vary slightly in color. Recently Western gorillas have suffered serious losses due to ebola.

2 diet

Their diet is largely, perhaps exclusively vegetarian: leaves, bamboo shoots, bark. Males may take in over 30 kg of food each day; females about 18 kg. These foods are not easily digested and gorillas do not have the gut adaptations that other species, e.g.. cattle, that have similar diets. However gorillas are almost certainly different in digestive adaptations than humans.
Eating may take up half the day; resting and digesting the remainder. Fossey reports some fruit and occasional fungi, grubs and snails also may be eaten --these are a very small part of the normal diet. (She comments on gorillas rejection of termites, treated as delicacy by chimps.)

3 habitat

Like all primates (but humans), gorillas are constrained to environments where their huge food supply is readily available. Gorillas are primarily terrestrial -- as adult feet suggest , living and sleeping on the ground in "nests" although some young animals and females may nest in trees.
Gorillas have small ranges and are not very territorial.

4 behavior

Observe their typical primate features--including manual dexterity and ability to stand upright for short periods. Also note their apparently placid, gentle temperament. (But read about Joe below.)

A. social organization

Gorillas are found in polygamous groups from several up to 20 or more. Typically there is one older male ("silverback"), some younger males, and a number of females and young. These "family" groups travel, feed, and rest together.
Groups may have overlapping ranges and young females may transfer to another group. Males leaving a group do not join another and each must start up his own by attracting females.
There are some reports of lone males attacking groups, killing infants (see infantcide and kin selection) and "abducting" the female. Dian Fossey suggested this is brought about by a high ratio of adult males to females.

B. reproduction

Gorillas are rarely observed mating, in contrast to chimps, and only the silverback mates with adult females. Younger males may mate with younger females not yet likely to become pregnant.
Gorilla sexual behavior involves less day to day competition than in chimp "society" where competition for mates is on a daily basis. (Hence larger testicles in the chimps?)

Competition among gorilla males is over the control of the entire family group -- not in mating with individual females. Thus we observe large gorilla males with prominent canine teeth --not for ripping up prey, but for threatening and attacking the competition males.

Reproductive rate is expectedly slow; Fossey reports females with 42 to 55 months between births. Gestation takes about 258 days. Zoos have had difficulty in breeding gorillas; females are very particular about mates and may not naturally know how to mother without appropriate social experiences.

Early experiences in most mammals determines not only skill at "mothering" (early zoo pregnancy scene) but may even influence self-identity. It is no surprise to me when a gorilla raised with humans as a human or pet -- like Koko (below) -- shows little interest in mating with a real gorilla! (See Harlow's work on attachment for example.) As several talking heads point out in the video, these zoo-raised gorillas are not gorillas.

C. aggression

Unlike the long Hollywood tradition of King Kong and Mighty Joe Young, Gorillas seem to be rather non-aggressive, though silverbacks will vigorously attack threats to their group, e.g. from a human or another gorilla. Adolescent males also may cause trouble. Joe, as you can see has lots of muscle but not all the bulk of an adult male enabling Joe to climb and escape zoo enclosures adequate for younger and older gorillas. Gorillas, like most animals out of their "natural" environment, behave in unpredictable ways.


The large canine teeth of the male are exclusively for competitive displays with other males. Note how easy it was for early observers to assume these animals were agressive carnivores. This illustrates the dangers of assuming we can easily infer function from form.

5 size

Gorillas--like orangs -- are highly dimorphic, i.e. show great sexual differences in size (dimorphism). Males weigh between 140 and 180 kg; females about one half that. This reflects competiton among the males for group control-- bigger males tend to drive out smaller ones and reproduce more frequently.

6 conservation

The "Gorilla" video reveals the serious problems facing survival of gorillas; loss of habitat due to human farming needs and the dangers of poachers after meat and souvenirs. Diseases like ebola can greatly reduce local populations.
Dian Fossey, alive when this video was made, spent a many years studying gorillas and working recklessly to preserve them. She was murdered in her camp in 1985. See Fossey (1983) and Montgomery (1991).
See Weber & Vedder (2001) notes below.

There is also recent info on the Aspinall foundation here, 5/09 or here. Check Youtube for recent Aspinall video.

(the Aspinall family still makes headlines, Nov. 2011)


7 psychological research--"mind?"

Gorillas were virtually unknown to European and American scientists until 1842. The famous Nobel Lauriate and physiologist, Sherrington, about 1917, published an account of the gorilla's brain and nervous system showing its great similarity to humans. this inspired lots of speculation on their intellect.

The National Geographic video shows footage from old films taken by Osa and Martin Johnson-- famous explorers and "bringem back alive" white hunters. In one segment of "Congorilla, 1932" they show the capture of two young gorillas headed for the San Diego zoo. They made a number of commercial films of their adventures, some of which are among the first films of African peoples and animals 1925-39.

Compared with chimps and other primates, little research has been done with gorillas. "Goma" one of the first zoo-born and home-raised gorillas is discussed in the video. It also includes the most famous recent project involving Koko a female that has been "taught" some manual signs. (Patterson et al, 1987). Although referred to at times as American Sign Language (ASL), informants who know ASL tell me, that there is little relationship to the signs used by Koko and ASL. Several have been insulted by the comparison. We will see a video on the acquisition of a dialect of human sign language (NSL), which is quite distinct from gorilla sign language (GSL)! For information on this see my comments and a transcript of a "conversation" with Koko.
Claims about these communicative behaviors should be interpreted with caution; anthropomorphism--putting a human interpretation on a nonhuman behavior-- is a potential problem. Gallup (1983) discussed in our readings, discusses the absence of mirror self-recognition in gorillas but not chimps. On other learning tasks, he reports gorilla performance is "largely indistinguishable from chimpanzees and orangutans. p.481"

tool use No examples of tool use are shown in this video and until recently it seems none was observed. Recently some observations have been reported showing some use of sticks as canes or probes.
Koko is also shown and discussed in the Chevalier-Skolnikoff, S. (1977) in connection with ape socialization potential.

Recent developments

The video shows a young Amy Vedder guiding a group of tourists into gorilla land. Recently Vedder and Bill Weber (2001) published a book on their experiences. Here is an excerpt from a review on
"Realizing that gorilla conservation was not a priority for a country facing staggering economic and development problems, they persuaded skeptical authorities that a program combining research, ecotourism and education could both protect these majestic primates and generate economy-boosting revenues. Their Mountain Gorilla Project, implemented over Fossey's objections, proved successful, with recent gorilla censuses showing dramatic population increases. Weber and Vedder's fascinating account of their years in Rwanda describes thrilling, sometimes heart-breaking gorilla encounters, and analyzes their painful relationships with Fossey with bracing honesty. But the book's larger, and more complex, subject is conservation in a war-ravaged postcolonial world struggling with increased competition for finite resources. Weber and Vedder ably portray Rwandan society, fraught with ethnic divisions and governmental corruption that not only threatened wildlife conservation but imperiled human safety. Their description of the 1994 genocide of Tutsis by Hutus based on reports from friends still in the country at the time is a chilling reminder that humans, too, are a fragile species. "We can't love animals or save wildlife," Weber and Vedder conclude, "without understanding the social, economic, and political context in which conservation occurs."

The Gomez text discusses mental abilities of gorillas extensively.

Chevalier-Skolnikoff, S. (1977). A Piagetian model for describing and comparing socialization in monkey, ape, and human infants. In S. Chevalier-Skolnikoff F. E. Poirier (Eds.), Primate bio-social development (pp. 159-187). New York: Garland Publishing, Inc.
Fossey, D. (1983). Gorillas in the mist. Boston: Houghton Mifflin.
Harlow, H. F., & Mears, C. (1979). The human model: primate perspectives . Washington, D. C.: Winston & Sons.
Gallup, G. C. (1983). Toward a comparative psychology of mind. In R. L.

Osa and Martin Johnson Safari Museum

Mellgren (Ed.), Animal cognition and behavior (pp. 473-510). Amsterdam: North-Holland.

Leyton, A. S. F., & Sherrington, C. S. (1917). Observations on the excitable cortex of the chimpanzee, orangutan, and gorilla. Quarterly Journal of Experimental Physiology, 11, 135-222.

Limber, J. (1977). Language in child and chimp? American Psychologist, 32, 280-295 (Reprinted in Sebeok, T. & Sebeok, J. (Eds.) (1980). Speaking of Apes (pp.1197-1218). New York: Plenum Press.). online PDF.

Montgomery, S. (1991). Walking with the great apes. Boston: Houghton Mifflin.

Patterson, F. G., Patterson, C. H., & Brentari, D. K. (1987). Language in child, chimp, and gorilla. American Psychologist, 42, 270-273. (But read my earlier paper first! Limber (1977), see above.
Weber, B., & Vedder, A. (2001). In the kingdom of gorillas: Fragile species in a dangerous land.