Wild Chimpanzee Tool Use

The Gombe Chimpanzees


Snow Monkeys


Collie's Bestiary

Odds 'n' Ends Page


The Primate Papers

ANTH 106: Primate Behavior
Prof. A. Zihlman
Copyright © 1999 B. Collie Collier

These are most of the papers from my Primate Behavior class. While the actual scholarly articles may be hard for the casual explorer to find, my papers on the articles mention some interesting behavioral research, and so might be of interest. Enjoy... it was a fascinating class.


Wild Chimpanzee Tool Use

Our current readings on tool use in chimpanzees are three articles by Boesch & Boesch, Alp, and Huffman & Kalunde. All the information comes from data collected in long-term studies. Boesch & Boesch comparatively discuss tool use and creation by wild chimpanzees in three long-term study locations. Alp briefly mentions chimpanzee tool use in the Sierra Leone, as well as cultural variation in wild chimpanzees. Huffman et al reports on the creation and use of a tool for predation by a chimpanzee, and includes some speculations regarding chimpanzee tool use.

Boesch & Boesch discuss tool use amongst the Tai chimpanzees, and compare it to Gombe and Mahale chimpanzee tool use, as all three areas are part of long-term studies. To avoid classification of nest-building as tool use, they give the following definition: "an object held in the hand, foot, or mouth and used so as to enable the operator to attain an immediate goal." They find that Tai chimps use tools more in feeding contexts than aggressively. The Tai chimps make tools from branches, stones, and twigs, since they do not have access to grass. Their ant dipping sticks allow them to scoop ants directly into their mouths. The chimps also use stick tools to inspect honey bee nests, disable and eat any adult bees, and to fish out hard-to-reach bits of food (such as honey, nut kernels, or bone marrow). They also open nuts with hammers of stone and wood. Comparison of tools used in different contexts (e.g., honey dipping or extraction of bone marrow) shows that the chimps specifically fashion tools for discrete uses, with individual variation in methodology.

As far as cross-cultural comparisons of observed tool creation and use, the Tai chimps use tools most frequently, followed by the Gombe and then the Mahale chimps. The Tai chimps are unique in that they alone pound objects with tools, and only they combine two different tool uses in retrieving a single food item. Their manner of ant dipping is also unique, as both other populations (Gombe and Mahale) transfer the ants from the dipping stick to the hand, and thence to the mouth. This explains the shortness of the Tai ant dipping tools, as compared to the other populations. Tai chimps do not fish for termites, but the researchers noted that the species of termite that the other populations fish for does not live in the Tai forest. Mahale chimps tend to modify their ant dipping tools while in the process of using them, as opposed to the Tai chimps, which tend to do more modifications, and to do so previous to usage. This would indicate the Tai chimps have an advanced understanding of the relations between objects.

The authors speculate that a demanding food retrieval technique (such as nut pounding) may require food sharing as a prerequisite to acquisition of the skill. Additional benefits of tool use (aside from food retrieval) may be defense from stings or bite wounds. Increases in tool modification may allow less selectivity in raw materials, whereas where materials are rare it is apparently easier to search for a remembered tool rather than search for a material and modify it. Finally, the authors note that there does not appear to be any ecological or genetic reason for differences in tool use among the 3 populations, and mention attribution of culture to chimpanzees as a result.

The pertinent parts of Alp's article are her discoveries of what appear to be modified ant-dipping wands near disturbed ant hills where the chimpanzee troop had recently been feeding. She did not see the tools used or created, however. Compared to recovered Mont Asserik, Bossou, Tai, and Gombe ant-dipping tools, only the Tai tools were significantly different from the Sierra Leone tools, being on the average less than half the length of the others. Alp notes cultural differences amongst wild chimpanzees, specifically that Tai chimps use a different technique for extraction of ants.

Huffman & Kalunde discuss the unique tool use of a 12 year old orphaned female chimpanzee to assist in small mammal predation. They describe the method of tool creation, as well as the tool's use to forcefully poke in a squirrel's hole to bring out the prey for capture and consumption. The authors noted that an unrelated, orphaned, 4.5 year old female traveling companion also received some meat. Huffman et al mention more common and skillful tool use by females than males, citing observed occurrences of tool use in other locations. The authors hypothesize that limited valued resources cause those without access (usually females and adolescents) to develop alternate ways of acquiring them, as demonstrated by the more skillful and common tool use of female chimpanzees. They note the possible importance of individual variation in problem solving skills, and conclude by calling for more research.

All of the articles note that several years of observation (i.e., long term studies) are required before any tool use is seen. It is the ability to identify individuals that has led to observations about sex-related differences in tool use. Furthermore, the availability of life histories of identified individuals allows for research into generational tool use, as well as comparisons of individual and populational variations in tool use and creation methodologies.

The Gombe Chimpanzees

This essay will summarize information gathered from the Gombe chimpanzee studies and show how this study relates to issues in life history from previous articles, e.g., Morbeck (1997). Current readings on the Gombe chimps are the articles by Goodall (1986), and Zihlman, Morbeck, & Goodall (1990). All the information within the articles comes from data collected in Goodall's long-term study (greater than 30 years at present) of the Gombe chimps, with specific attention paid to life history variables. Goodall gives thumbnail sketches and photographs of observed life events of a few of the individual chimps. Zihlman et al examines the recovered skeletons of 7 of the Gombe chimps, and uses them to discuss chimp anatomy, growth and development, and behavior. The effect of the individual's psychosocial environment (gleaned by long-term observation) combined with the data on the skeletons to provide a deeper view of each individual's life and social history. Zihlman's careful selection of individuals includes both sexes and a wide range of ages covering all the stages of growth and development in life.

Goodall's 1990 article gives summaries of the life histories of 28 individual chimpanzees. Through these short semi-biographies we also get a concentrated view of the social environment at Gombe, as lived by the various individuals. Goodall chooses both high- and low-ranking individuals, of both sexes, and shows how rank varies with age. This diversity allows one to see both broad patterns of behavior (such as how rank affects social skills) and individual variations (such as Passion's habit of eating infants).

The Zihlman et al article covers a similar vein. It presents skeletons from a variety of individuals, and connects the condition of each skeleton to the observed lifetime behavioral patterns for each chimpanzee. The state of the skeletons also demonstrates possible reasons for non-observed occurrences, such as Flint's lack of skeletal development potentially explaining his extreme dependence on his mother, Flo and his death 3 weeks after hers. The effects of nutrition, injury, and disease are demonstrable on the individuals' skeletons, as well as possible ramifications these have on each individual's observed reproductive success. The seven chimpanzee skeletons examined in the article are compared to skeletons of both captive and free-ranging individuals. There are several tables of individual comparisons (e.g., bone lengths, widths, diameters, weights, and mineral indexes) for the skeletons of chimps of similar age and sex, which also allows computation of averages. Zihlman also mentions old, healed bone fractures and bite wounds, loss of dentition due to age, asymmetry in lateral bone growth, and the effects of disease on bone growth. Interestingly, none of the examined skeletons were precisely 'average'; they all had something that made them unique in some fashion. As Zihlman notes in the introduction to the article, it is these individual variations, adding up over time, that create evolutionary change. The combination of individual life history occurrences (as recorded in the bones and teeth of those individuals) and Goodall's long-term behavioral field study gives a clearer picture of the Gombe chimps' endeavors to survive through the different life stages and achieve reproductive success. As the skeletons demonstrate, individual survival can be problematic; as the long-term field study shows, survival of the individual does not assure reproductive success. Evolutionary success is dependent upon individual lives. Each individual's life history reflects a wide variety of factors; nutrition, disease, injury, and their physical and social environment.

The Goodall and the Zihlman et al articles illustrate the life history approach clearly, as it is delineated by Morbeck (1997) in our reader article. The Gombe chimpanzee articles contain collected information that is both multi-leveled and multi-generational: factual data from physical examination (e.g., Zihlman's anatomy comparisons) and long-term field observations (e.g., Goodall's study). The focus is on individually recognized organisms and their attempts to survive and reproduce. By recording lineages, generational observations can be made, as well as speculations on populational and biological change. The authors' observations on life stages, survival rates, and reproductive successes of different individuals allow whole lives to be examined as parts of a social whole. Because of the multi-generational approach the authors adopt, they can study natural selection both broadly within chimpanzees as a species, and more specifically in one local group: the Gombe chimpanzees.


Our current readings on gibbons are sections of Zihlman's natural history of the great apes, and Raemaekers' study of sympatry in gibbons. Both articles use a life-history perspective. Zihlman compares physical characteristics, individual variations, and sex-specific social behaviors for male, female, and juvenile gibbons. Raemaekers uses time allocation budgets and study of individuals to examine sympatry in gibbons.

Zihlman's article compares the lar gibbon to some of the other great apes. Of the great apes, the lar gibbon is the lightest, but male and female gibbons are unique amongst the apes for being almost identical in weight. Unsurprisingly the birth weight of gibbons is also the least, and the females reproduce for the first time soonest. Their gestation length, while the shortest, is fairly close to the others, and weaning and birth interval are only one year less than several of the other apes mentioned. They live for about 30+ years, compared to the 40+ of the others.

Gibbons live in the rain forests of Malaysia and the islands of Malaysia, Indonesia, and the Indo-China mainland. The fossil record shows that they diverged from the other hominoids about 15-18 mya. Gibbons all brachiate, are frugivorous, and can feed on young leaves. Anatomically speaking, gibbon females have a (possibly statistically insignificant) tendency towards longer trunk length, males towards larger chest girth and shoulder breadth; there are also sex differences in pelage. There is wide individual variation in cranial capacity, although averages between the sexes are similar. Lar males have slightly longer canines than females; besides that species the pronounced canine size/shape and jaw morphology are quite similar amongst the gibbons. Siamangs have laryngeal sacs. There are few visible differences between adult and juvenile gibbons.

Gibbon social groups consist of a single male-single female mated pair and several offspring. Infant care falls almost exclusively to female gibbons, although male siamangs may carry young in its second year. Offspring leave the natal group to establish their own territories. In some species females travel first (perhaps allowing primary access to energy-rich fruit). Lar females in late pregnancy and early postpartum are dominant in feeding to males; there are also differences between the siamang sexes in feeding speed and duration. Both sexes are intolerant of members of the same sex in the neighborhood and physically and/or vocally defend their ranges. Vocalizations are in duets, and are used to differentiate individuals, attract mates, strengthen the group's female-male bond, and locate, define, and maintain territorial boundaries. However, males appear to be more active in territorial defense; they call and chase longer, and initiate agonistic encounters more frequently, than females. The disparity of damage to the teeth and bones of each sex shows the results of their different life behaviors.

Raemaekers' study shows that the siamang is sympatric with either the lar or the agile due to a difference in their body sizes, which causes a difference in diets. Because the siamang is larger travel is energetically more expensive for it than for the lar. The siamang body is also stockier in shape and loses heat more slowly, allowing it a lower energy per unit diet, for example, less fruit and more young leaves. It consequently eats for longer daily rates than the lar, travels shorter daily routes, and has a smaller range. The efficient grinding molars of siamangs are more similar to other leaf-eating primates than to the frugivorous lar, and siamang mouths are larger than those of lar, allowing more efficient throughput of leaves. Thus siamangs can consume leaves more rapidly than lar can. Lar, however, can eat more of the rare but energy-rich fruit as rapidly as gibbons eat leaves. Because they also travel further and have larger ranges they can seek out fruit more often, and thus have a wider food choice than gibbons. Raemaekers speculates that the close cohesion of siamang troops is because they all travel the same well-known routes to food, due to the need to conserve energy. Lar do not need to conserve energy so much, and thus have less troop cohesion, spreading out more as they travel.

Raemaekers also speculates on parallels between the gibbons and the African apes, regarding the relationship between body size and ecology. However, he gives several cautions against this, noting the different habitats and social systems used by chimpanzees and gorillas, as opposed to the gibbons being all alike.

Due to comparing individual variations and taking careful, statistically significant data over years, Raemaekers can note individual time allocation as well as compare range use and daily travel rates by the larger social group. Keeping in mind individual variations, Zihlman can use long-term studies for data to note physical differences between the sexes, and to attempt to explain the evolutionary and reproductive importance of sex-related differences in behavior. Social systems and environmental responses are being more fully understood as a means for improved reproductive outcome. Thus Zihlman and Raemaekers both demonstrate the benefits of the life-history perspective in long-term studies.

Comparison/Contrast of the Behavior of Japanese and Texan Snow Monkey Troops

On Wednesday the Primate Behavior class saw a film called "Mozu." This film concerned a specific macaque from a Japanese snow monkey troop that has been extensively studied for many years by Japanese scientists. We have also read Pavelka's book concerning the monkeys of Texas. The Texas macaque troop was originally descended from the Japanese macaques, and a contrast and comparison of the respective behaviors of the 2 troops is of interest to scientists, from the life history perspective.

The Japanese troop was lightly described in the film. For example, the macaques are usually ground-dwellers, and become arboreal in heavy snow. In the winter when food is scarce, the monkeys are reduced to eating bark and twigs. The Japanese macaques also have a river, and a heated pool -- and there are scenes of the juveniles not only dog-paddling, but also swimming underwater. Visually, the monkeys appear quite large, with thick, fluffy coats. Behaviorally speaking, there are a few noteworthy facts that demonstrate difference from the Texas troops' behaviors. For example, the alpha male signals incipient troop movement by climbing a tree and shaking it violently. During the breeding season, male-male fighting is quite fierce. However, some males join the troop only during mating season, even when they are successful in battle with the troop's alpha male, leaving the troop for the peripheral all-male troops after the breeding season is over. Finally, in the film there are two mentioned instances of a very old animal leaving the troop to live alone until death.

In contrast, the Texas monkey troop has a few noteworthy differences. Visually they are rather smaller looking. Their light coats (due to the heat) give them a lighter, sleeker look. They have running water that appears in the photos to actually be deep enough to immerse themselves. However, Pavelka makes no note whatsoever of any swimming behaviors in the Texas macaques. There is no mention of the alpha male shaking trees to signal incipient troop movement either. However, this is probably due more to the lack of large, heavy trees and underbrush, or to the limited geographical area. Also, there is no need for the Texas troop to become more arboreal due to seasonal snows. Their food supply is more regular and varied. Pavelka notes this may have subtly altered their feeding behaviors from those of the Japanese troop, although she also notes that this is currently not completely known. However, Pavelka mentions that male-male fights do not seem to be as damaging as males chasing females during breeding season. Furthermore, she mentions no instances of old animals leaving the main troop to live alone until death, nor of alpha males leaving the main troop after breeding season to re-join the all-male peripheral troop. Indeed, the Texas macaques seem to have more natural predators than the Japanese troops do, causing a high mortality rate in the Texan peripheral all-male troop, and a new danger call indicating 'snake' to be learned by the troop members.

There are several behaviors the two macaque troops still have in common, however. In both the book and the film there is extensive mention of the strength of mother-child bonds, of the social importance of matrilineal lines, and of the females not leaving the troop of their birth. The restrictive behaviors of low ranking females towards their infants was also mentioned, as was the temporary behaviors (e.g., carrying and grooming) of mothers with dead infants. Thus one can see, by studies that extend over years, that while behavior changes somewhat to reflect the environment, the strong social bonds passed on by the troops' females from mother to child will exist regardless of habitat. This kind of information would not be feasible in a research project that did not include the life histories of the macaques involved in the studies.


Our current readings on Orangutans are sections of the natural history article on great apes by Zihlman, and two articles by Chevalier-Skolnikoff et al and Galdikas. All the information comes from data collected in long-term studies with attention paid to life history variables. Zihlman discusses orangutan anatomy, growth and development, and behavior. Chevalier-Skolnikoff et al concerns possible evolutionarily selected aspects of higher intelligence in orangutans, based on a Piagetian model. Galdikas reports on the feeding habits of lowland swamp orangutans, contrasting them to the better studied mountain orangutans.

Zihlman's article notes orangutans live in rain forests in Borneo and Sumatra; in the Pleistocene and Holocene their ranges were more extensive. Orangutans diverged from the other great apes at about 9-11 mya. They are large-bodied forest canopy dwellers, mainly frugivorous, and display extensive climbing, reaching, and hanging behaviors. They have pronounced sex differences in body weight and proportion. Females are 45% of male body weight, and have corresponding differences in brain size, chest girth, long bone lengths, and proportions of muscle, bone, and fat. Females also mature more quickly (about 10 years) than males (about 15 years).

Orangutans are unusual socially due to their solitary natures. Their behaviors are sex-related, with the heavier males using the ground, tree swaying, and lower levels of the forest. Males also tend to sit on branches and pull food to them; females hang and pluck food. The Galdikas article is referenced re: diet and feeding habits, and Zihlman's conclusions mirror Galdikas' re the relationship between body weight, diet, and solitariness. Zihlman goes on to note which sex is social, and when in the life cycle this occurs. Adolescent females and immature males are the most social (about 40% of their time, usually with other females); adult males are the least (about 2% of their time, only when consorting with females). Adult males avoid each other through vocal calls, but they are quite aggressive towards each other in the presence of females. Healed wounds indicate the males do fight. The evolutionary reasons behind the physical differences of males (throat sac, facial configuration) are not currently known.

Chevalier-Skolnikoff et al find advanced cognitive abilities in orangutans to have evolved as a general adaptation for solving predicaments encountered in daily life. This trait was probably primarily selected for due to problems with locomotion, but it also contributes to solutions for quandaries encountered while feeding, nesting and rain-sheltering, having agonistic encounters, and in mother-infant interaction.

Galdikas' article finds orangutan solitariness to be a result of large body size and a predominantly frugivorous and opportunistic diet. Female grouping behavior increases with use of permanent resources (no inter- individual competition) and decreases with fruit consumption (where groups consume fruit faster than individuals do). The largest males are the most solitary; small adolescent females are almost social.

The amount of time expended by orangutans in daily activity is not sex related; what they do is. Only adult males descend to the dangerous ground for termite eating (a more concentrated high calorie food) and travel (which conserves energy). Males also travel further between food sources than females, although both sexes use about the same number of food sources daily. Females use a wider variety of foods, due to reproduction costs. Occasionally females exploit seasonally favored foods. This requires them to lengthen their day ranges and overlap home ranges. Females also travel more slowly than males, due to being followed by offspring.

Galdikas' article is based on fieldwork she has done during her on-going long-term study of orangutans. She has been watching individuals and taking careful, statistically significant data over years. Chevalier-Skolnikoff et al (which includes Galdikas) similarly procured data to analyze certain types of significant behavior. Zihlman bases her behavioral data on long-term studies with a focus on life-history, which includes Galdikas' work. Thus Zihlman (and the others) can use such studies for data to note physical differences between the sexes, and to attempt to explain the evolutionary and reproductive importance of sex-related differences in behavior. As a consequence of the life-history perspective being used in long-term studies, social systems and environmental responses are being more fully understood as a means for improved reproductive outcome.


Last Updated: Fri, March 31, 2000