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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.
Gibbons
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.
Orangutans
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.
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