close

Вход

Забыли?

вход по аккаунту

?

Effects of early rearing conditions on problem-solving skill in captive male chimpanzees (Pan troglodytes).

код для вставкиСкачать
American Journal of Primatology 72:626–633 (2010)
RESEARCH ARTICLE
Effects of Early Rearing Conditions on Problem-Solving Skill in Captive Male
Chimpanzees (Pan troglodytes)
NARUKI MORIMURA1,2 AND YUSUKE MORI2
1
Wildlife Research Center, Kyoto University, Uki, Kumamoto, Japan
2
Chimpanzee Sanctuary Uto, Kumamoto, Japan
Early rearing conditions of captive chimpanzees characterize behavioral differences in tool use,
response to novelty, and sexual and maternal competence later in life. Restricted rearing conditions
during early life hinder the acquisition and execution of such behaviors, which characterize the daily
life of animals. This study examined whether rearing conditions affect adult male chimpanzees’
behavior skills used for solving a problem with acquired locomotion behavior. Subjects were 13 male
residents of the Chimpanzee Sanctuary Uto: 5 wild-born and 8 captive-born. A pretest assessed bed
building and tool use abilities to verify behavioral differences between wild- and captive-born subjects,
as earlier reports have described. Second, a banana-access test was conducted to investigate the
problem-solving ability of climbing a bamboo pillar for accessing a banana, which might be the most
efficient food access strategy for this setting. The test was repeated in a social setting. Results show that
wild-born subjects were better able than captive-born subjects to use the provided materials for bed
building and tool use. Results of the banana-access test show that wild-born subjects more frequently
used a bamboo pillar for obtaining a banana with an efficient strategy than captive-born subjects did. Of
the eight captive-born subjects, six avoided the bamboo pillars to get a banana and instead used,
sometimes in a roundabout way, an iron pillar or fence. Results consistently underscored the adaptive
and sophisticated skills of wild-born male chimpanzees in problem-solving tasks. The rearing conditions
affected both the behavior acquisition and the execution of behaviors that had already been acquired.
Am. J. Primatol. 72:626–633, 2010.
r 2010 Wiley-Liss, Inc.
Key words: rearing condition; problem-solving skill; cognitive task; chimpanzees
INTRODUCTION
Restrictive rearing conditions in captivity affect
chimpanzee (Pan troglodytes) behavior, even years
after restrictions were terminated [Brent, 2001;
Turner et al., 1969]. Videan [2006] reported that
wild-born chimpanzees built and used beds significantly more than captive-born individuals. Bed
building is a socially facilitated learned behavior
acquired during the first years of life. Menzel et al.
[1970] pointed out that wild-born chimpanzees were
better at performing a task requiring the use of tools
than captive-born (restriction reared) individuals
were. Brent et al. [1995] demonstrated by using a
large sample size of 45 chimpanzees that behavioral
differences in tool-using ability between captive- and
wild-born chimpanzees appeared even in less-restrictive rearing environments, indicating that rearing conditions engender differences in later tool-use
abilities. Rearing conditions affect other behaviors
related to sexual and maternal competence [Brent
et al., 1996]. Nursery-reared chimpanzees engaged in
sexual behavior less than mother-reared individuals
did [Baker et al., 2000]. Consequently, restricted
rearing conditions in early lifetime make it difficult
r 2010 Wiley-Liss, Inc.
to acquire some behavioral repertoires; the rearing
conditions, thereby, strongly affect the daily life of
captive chimpanzees.
The acquisition of behavior and its expression
characterize the overall performance of captive
chimpanzees in daily life [Pruetz & McGrew, 2001].
Anecdotal records suggest that restricted rearing
conditions in early life might affect the expression of
behavior that an animal acquires. At the Chimpanzee
Sanctuary Uto (CSU), Japan, a nursery-reared
female moved around by jumping only on concrete
areas of floors in an outdoor compound, using such
Contract grant sponsor: Japan Society for the Promotion of
Science (JSPS) and the Ministry of Education, Culture, Sports,
Science and Technology (MEXT) of Japan Grants-in-Aid for
Scientific Research; Contract grant numbers: 19650225;
9330159; Contract grant sponsor: 2008 IPS Captive Care Grant.
Correspondence to: Naruki Morimura, Wildlife Research
Center, Kyoto University, 990 Ohtao, Uki, Kumamoto, 8693201, Japan. E-mail: nmorimura@wrc.kyoto-u.ac.jp
Received 15 April 2009; revised 16 January 2010; revision
accepted 2 February 2010
DOI 10.1002/ajp.20819
Published online 4 March 2010 in Wiley InterScience (www.
interscience.wiley.com).
Problem-Solving Skill in Chimpanzees / 627
areas as stepping stones. It took about 1 month for
her to become accustomed to walking on the ground
[CSU, unpublished observations]. Another nurseryreared female at CSU used to walk on a beam while
gripping the bars of the ceiling in an outdoor
compound, instead of brachiating. Even though the
chimpanzees had acquired behavioral skills for
walking and hanging, their behaviors differed markedly from those of wild chimpanzees. Moreover,
systematic studies of macaques revealed that
early rearing conditions affect problem-solving behavior and their underlying cognitive processes.
Isolation-reared rhesus monkeys (Macaca mulatta)
adjusted more slowly to reinforcement contingencies
[Lichstein & Sackett, 1971] and performed poorly on
complex tasks, such as an oddity learning set [Gluck
et al., 1973]. Novak and Sackett [2006] pointed out
that behavioral and cognitive problems in these
isolation-reared monkeys were not simply the result
of sensory deprivation attributable to a lack of
opportunity to experience manipulating objects or a
lack of exposure to social stimuli.
The findings described above imply that chimpanzees and some other primates develop a behavioral tendency in the exertion of acquired behavior
that is characterized by the early rearing condition.
Little attention has been devoted to the effects of
early rearing conditions on acquired behavior in
captive chimpanzees. This study specifically addressed the effect of early rearing conditions on
task-solving behavior of captive chimpanzees. The
performance of tasks by wild- and captive-born
subjects in this study was compared directly. The
groups raised in the wild vs. those raised in captivity
differed in their first few years. In post-infancy,
almost all chimpanzees experienced isolation and all
experienced biomedical testing; all had resided in an
old-fashioned captive condition for most of their
post-infancy life. All chimpanzees were living successfully in a social group under a less restrictive
condition during the experiment period. A more
likely explanation could be that differences in their
rearing experiences from birth to 2–3 years of age
would be the cause if group differences were found.
The experiment examined the behavioral skill of
chimpanzees used for accessing food by presenting a
banana placed on the top or bottom of a bamboo
pillar. Climbing a tree or a pillar is a common
behavior both in the wild and in captivity. Accessing
the roof of an outdoor compound by climbing a pillar
or fence was an acquired behavioral skill in daily life
for all subjects. In addition, the subjects were
presented with alternatives for their access: climbing
an iron pillar or fence at another place or moving
along the ceiling horizontally by brachiation.
Furthermore, the experiment was conducted in a
social situation. This setting enabled every member
to learn repeatedly, through mutual observation,
how to access a banana. Under those conditions, the
strategies used in solving the tasks were assessed in
groups of wild- and captive-born chimpanzees.
Additionally, to verify the behavioral differences
between wild- and captive-born chimpanzees, described in reports of earlier studies by Videan [2006]
and Brent et al. [1995], their bed-making and toolusing abilities were tested using a one-trial simple
task before the banana-access test. A correlation of
behavioral tendencies between bed-building and
tool-using abilities and behavioral skills for accessing
a banana, if detected, would provide complementary
evidence, supporting the effects of early rearing
conditions on banana-access test results. However,
the experimental design of this study makes it
difficult to measure the effects of early rearing
conditions directly with counterbalancing of other
possible influential factors, especially because of the
small sample size, comprising individuals of a single
sex. Consequently, the conclusions obtained from
this study are expected to be more suggestive than
definitive.
METHODS
Study Subjects and Sites
The chimpanzees examined in this study were
housed at the CSU (a former laboratory facility). All
subjects (n 5 13) were males, including 8 captiveborn adults (Group A) and 5 wild-born adults (Group B).
Group A was an all-male group of nine individuals.
The remaining wild-born chimpanzees in Group A
had participated in the experiment, although the
records were eliminated from the data analysis of
the study. Captive-born subjects included both
mother- and nursery-reared individuals (Table I).
Mother-reared subjects (n 5 5) were reared for more
than 1 year after their birth (mean7SEM 5
14707497.9 days) by wild-born mothers in a social
group. Nursery-reared subjects (n 5 3) were separated from their mothers for the first year
(mean7SEM 5 103759.2 days) and reared in a
nursery group.
The housing types were classified as traditional.
The outdoor compounds of Groups A and B were,
respectively, 128 m2 (W:D:H 5 10.0:12.8:3.8 m) and
117 m2 (W:D:H 5 8.5:12.8:3.8 m). Both compounds
were covered with iron mesh fences. Some grass
and shrub vegetation was present on the ground.
Climbing structures of logs, used fire hoses for
moving, hammocks made of burlap sacks, and
several feeding devices were present in the compound for environmental enrichment. Indoor rooms
were
old-fashioned
small
cells
of
4 m2
(W:D:H 5 2.0:2.0:2.7 m). The subjects were isolated
in indoor rooms from evening until the next
morning, but they were able to communicate
through the iron bars with neighboring individuals
by visual and physical contact. Food and water were
not controlled for the study. The care and use of the
Am. J. Primatol.
Am. J. Primatol.
August, 2004
June, 2003
A
B
Group
Time
of group
formation
16
18
20
21
21
24
Mikota
Kanao
Takashi
Norihei
Kazuya
Kenji
26
26
27
27
30
16
Minato
Shiro
Goro
Norio
Naoya
Takabo
15
James
Name
CSU,
Japan
CSU,
Japan
CSU,
Japan
CSU,
Japan
CSU,
Japan
CSU,
Japan
CSU,
Japan
CSU,
Japan
Africa
Africa
Africa
Africa
Africa
Age at the
study
Birthplace
1983
1983
1983
1983
1980
–
–
–
–
–
–
–
–
Arrival
year in
Japan
2000
2000
2000
2000
2000
–
–
–
–
–
–
–
–
Arrival
year
at CSU
(Yes)
(Yes)
(Yes)
(Yes)
(Yes)
0
390
205
388
106
1,460
2,920
2,190
Mother
rearing
(days)
TABLE I. The Rearing Experience of 13 Male Chimpanzees in the Study
n.a.
n.a.
n.a.
n.a.
n.a.
Yes
Yes
Yes
Yes
Yes
No
No
No
Nursery
rearing
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Isolation for
biomedical
experiments
Rearing experience
Yes
Yes
Yes
Yes
Yes
Yes
No
Yes
Yes
Yes
Yes
Yes
Yes
Experience of
biomedical
experiments
No
No
No
No
No
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Social living
before the present
group
628 / Morimura and Mori
Problem-Solving Skill in Chimpanzees / 629
chimpanzees conformed to the Guide for the Care
and Use of Great Apes of the Chimpanzee Sanctuary
Uto, Kumamoto, Japan. This experiment was performed with CSU approval. The guide is compiled to
include the ethical policy of the Primate Research
Institute, Kyoto University, and domestic laws
related to welfare and management of animals.
Data Collection
Pretest: The test consisted of two one-trial
tasks––a bed-building task and a tool-using task.
Each task was conducted for each subject in an
indoor room at 5 pm. In the bed-building task, two
natural plants (bamboo branches and straw) and two
artificial objects (burlap sack and cotton sheet) were
provided as bed material because material preferences might affect bed-building performance. Those
objects were selected in the contrast of unfamiliar vs.
familiar and natural vs. artificial. Straws and towels
of cotton sheets were not provided except for the
pretest. Bamboo was provided occasionally as environmental enrichment. A burlap sack was sometimes
provided, especially for the nursery group, as a
blanket during the night. The sizes of the bamboo
stalk, fascicle of straw, burlap sack, and towel were,
respectively, approximately 1.5 0.5 m, 1.0 0.2 m
diameter, 0.8 1.0 m, and 1.0 2.0 m. Each of the
four materials was provided only once, and on a
different day. Providing objects without food provisioning in an indoor room was an unusual event for
the subjects, during the study period. The task
performance was recorded within 5 min after providing
the material. During the period, the subjects who
had made a bed or a bed-like circle structure using
the material and/or those who used it as a bed were
judged as successful. The tool-using task was such
that a subject drank orange juice from a bottle by
dipping a wooden stick during the routine food
provision period in the evening. Before starting the
task, an experimenter passed a wooden stick
(approximately 30 cm length and 0.5 cm diameter)
to a subject in an indoor room. The stick-like object
of wood was familiar because some vegetation in the
outdoor compound was freely accessible for the
subjects. The task was started when the experimenter placed a bottle (approximately 20 cm height and
7 cm diameter) filled with orange juice in front of the
cage door. Whether a subject drank juice from the
bottle using the stick was observed. Successful
subjects used the stick as a tool within 5 min from
the beginning of the test period. The task was done
only once for each subject.
Banana-access test: Three bamboo pillars with
no branches (approximately 6 m height and 8 cm
diameter at breast height) were fixed in each outdoor
compound of Groups A and B. The 3 pillars were
more than 3 m distant from each other. Although
some structures and fixtures for climbing up to the
ceiling of the outdoor compound were present, no
object that could aid climbing was placed within 1 m
from a bamboo pillar. The pillars were driven straight
into the ground. The top was secured to an iron bar on
the ceiling using a nylon rope. Two bananas were tied
with a nylon rope at the top and bottom of the pillar.
To prevent subjects from finding the upper banana of
each pillar from an entrance gate when they were
introduced into a compound by opening the gate, the
upper banana of each pillar was fixed at the opposite
side of the pillar from the entrance. Bananas at the
pillar bottoms were fixed at about 1 m height from the
ground facing the entrance, enabling subjects to find
them easily. The test was conducted in a reunited
situation of a group in the morning, when they were
brought together in the outdoor compound by moving
them one by one from each indoor room. The test
began when a first individual entered the compound
and lasted until subjects had consumed all six
bananas. Individuals in the first half of the order
possibly obtained bananas more easily than those in
the last half. Consequently, the test was repeated until
all subjects had consumed more than 10 bananas by
controlling the introduction order. The subjects’
behavior was observed and recorded throughout the
series of tests using a digital video recording device
(DCR-SR3000; Sony Corp., Tokyo, Japan).
Statistical Analysis
To evaluate group differences, we compared the
number of each measured variable for all individuals
from Groups A and B. For the pretest, a success score
(0–1) was calculated for each subject for comparison
between the two groups using a non-parametric
Fisher’s exact test with statistical analysis software
R [R Development Core Team, 2007]. Data of the
banana-access tests were analyzed in terms of
physical skill, experience in social setting, age, and
the early rearing condition (origin). A group comparison was done fundamentally using a non-parametric
Mann–Whitney U-test, because the subjects in a
group to be tested were fewer than five individuals in
some analyses. A comparison of ages of the two
groups was tested using Student’s t-test. The
significance level was set to 0.05.
RESULTS
In the bed-building task of the pretest, two
subjects of Group A and four of Group B showed bed
building or related behavior within the first 5 min.
Bamboo, a familiar and natural object, was used as
bedding material by four individuals in Group B
(Fisher’s exact test, P 5 0.007). A burlap sack, a
familiar artificial object, was used by each of two
individuals in Groups A and B (Fisher’s exact test,
P 5 0.510). Straw, an unfamiliar and natural object,
was used by three individuals in Group B (Fisher’s
exact test, P 5 0.035). No subject used the towel, an
Am. J. Primatol.
630 / Morimura and Mori
Number of bananas consumed
unfamiliar and artificial object. They showed bedbuilding behavior, such as holding, stepping on, and
shaping in a circle on the floor around them. The
remaining subjects responded by dropping it on the
stairs leading down to the entrance of the room,
displaying it, and chewing it. Subjects of Group B
used three of four materials for bed building. Each of
the four subjects of Group B used more than two
types of material for bed building among three
materials. In contrast, two individuals of Group A
who had succeeded at the task used only the burlap
sack as bedding material. In the tool-using task,
three of eight subjects of Group A and all five
subjects of Group B drank juice using a wooden stick
that had been provided as a tool. Subjects of Group B
were better at the task of using tools than subjects of
Group A were (Fisher’s exact test, P 5 0.044).
The banana-access test was repeated for 27 and 23
sessions in Group A and B, respectively; each subject
received more than 10 bananas. In all, 285 cases of
accessing a banana by 13 subjects were analyzed. The
average quantities of bananas consumed by subjects of
Groups A and B were 18.4 and 27.6, respectively,
(Mann–Whitney U-test, U 5 17.5, P 5 0.713), although
the total number of bananas that each subject
consumed differed greatly among subjects, presenting
a range of 10–51. All subjects climbed to access a
banana at the top of the bamboo pillar, ranging from
25–85% in the total consumption for each subject.
The banana-accessing behaviors were categorized as climbing the bamboo, an iron pillar, or fence,
and moving horizontally by walking or brachiation.
These three behavioral types were used to determine
the strategies for food access that were examined
in the study. Group differences in each strategy for
accessing a banana appeared in the bamboo use
among three strategies (Mann–Whitney U-test,
U 5 3.5, P 5 0.011; Fig. 1). Two subjects in Group A
and five in Group B used a bamboo pillar for
accessing a banana. Subjects of Group B were better
at the bamboo use in solving the task than subjects of
Group A (Fisher’s exact test, P 5 0.016). The remaining two strategies were not different between the two
groups (Fisher’s exact test, iron pillar/fence,
P 5 0.385; walking/brachiation, P 5 1.000).
To determine the physical skill necessary for
accessing the banana, the respective values of
consumption of bananas at the bottom of bamboo
pillars by walking were compared between the two
groups. The average quantities of bananas at the
bottom consumed by subjects of Groups A and B
were 9.0 and 13.8, respectively (Mann–Whitney
U-test, U 5 13.5, P 5 0.338). In addition, among
seven subjects that used bamboo, the banana
consumption by climbing up a bamboo pillar was
not different between the two groups (Table II). The
remaining two strategies showed a similar tendency.
The experience of the test, namely the number
of bananas consumed before taking each of three
strategies for the first time, was not different among
subjects of the two groups (Table III). The strategy of
moving horizontally (walking/brachiation) required
the least experience. Of the 13 subjects, 10 adopted
the strategy for the very first access to a banana with
no experience. Of the 7 subjects that used bamboo, 4
TABLE II. Comparision of Group A and B: Banana
Consumption by Strategy for Accessing a Banana in
the Banana-Access Test
Group A
Strategy
n
Bamboo pillar
2
Iron pillar/fence
8
Walk/brachiation
8
Group B
Median
(Range) n
7
(4–10)
3
(1–7)
10
(3–34)
5
4
5
Median
(Range)
10
(3–19)
1.5
(1–3)
10
(5–39)
U
P value
3.5
0.558
7.5
0.136
19.5
0.942
GroupA(n=8)
GroupB(n=5)
**
TABLE III. Comparison of Group A and B Individuals: Banana Consumption as an Experience
Before Using Each of Three Strategies for the First
Time in the Banana-Access Test
Group A
bamboo
iron pillar/fence
walking/brachiation
Banana access strategies
Fig. 1. Comparison of three strategies for getting a banana
between Group A (n 5 8) and B (n 5 5) subjects in the bananaaccess test. Group B banana consumption per individual using a
bamboo pillar differed significantly from that of Group A. The
error bars represent the standard error of the mean of banana
consumption.
Am. J. Primatol.
Strategy
n
Bamboo pillar
2
Iron pillar/fence
8
Walk/brachiation
8
Group B
Median
(Range) n
4
(2–6)
2
(0–9)
0
(0–5)
5
4
5
Median
(Range)
1
(0–20)
4
(0–22)
0
(0–2)
U
P value
3.0
0.434
13.5
0.668
15.5
0.373
Problem-Solving Skill in Chimpanzees / 631
used the strategy with the earlier experience of
getting fewer than 3 bananas, as did 8 of 12 subjects
that used the iron pillar or fence. Consequently,
repetition of the test in a social setting did not aid
subjects’ experience of climbing a bamboo pillar.
In the test, subjects showed a strategy by which a
subject got two bananas at both the top and bottom of
a bamboo pillar in a sequential movement. For
example, a subject climbed up to access a banana at
the top of a bamboo pillar after getting a banana at
the bottom of the pillar. The sequential gathering of
two bananas at a bamboo pillar can be recognized in
the situation in which a subject was highly motivated
to get them. In the sequential gathering, climbing up
and down a bamboo pillar for accessing food was the
most efficient strategy. In contrast, moving to an iron
pillar or fence for the remaining banana at a bamboo
pillar after getting a banana at the bamboo pillar is a
roundabout way. In all, 52 cases of sequential
gathering were observed in the test. All subjects but
one (Group A) showed sequential gathering. Sequential gathering was more frequent in Group B than in
Group A (Table IV). In 33 of 52 sequential gatherings,
the subject used a bamboo pillar for climbing up and
down. Bamboo use in the sequential gathering was
also more frequent in Group B than in Group A. All 7
subjects using bamboo in the sequential gathering
showed a sophisticated strategy after a few experiences of getting bananas in a roundabout way 0–2
times. Consequently, the physical skill and the
experience before adopting the strategy did not differ
among the seven subjects that used bamboo in the
sequential gathering.
Table V presents results for each subject in the
pretest and the banana-access test. Subjects of Group
B were consistently better at solving tasks than
subjects of Group A. The average ages of subjects of
Group A and B were 18.9 and 27.2, respectively
(t-test, t13 5 –5.4, Po0.001).
DISCUSSION
The series of tests used for this study demanded
each participant’s decision-making for solving tasks.
Results of the pretest and the banana-access test
TABLE IV. Frequencies of Vertical Climbing (Up/Down) with Experience of a Sequential Gathering between
Group A and B in the Banana-Access Test
Group A
Group B
Behavior in a sequential gathering of bananas
n
Median (Range)
n
Median (Range)
U
P value
All vertical climbing
7
5
0.017
2
6
(3–14)
1
(0–2)
4
(3–11)
3.0
Vertical climbing experience before using a
bamboo pillar for the first time
Bamboo pillar climbing
2
(1–5)
1.5
(1–2)
1
(1)
3.5
0.539
0.0
0.049
2
5
5
TABLE V. Summary of Results for the Pretest and Banana-Access Test Subjects
Pretest
Bed-building
Group
Subjects
Origin
A
James
Minato
Mikota
Kanao
Takashi
Norihei
Kazuya
Kenji
Shiro
Gorou
Norio
Naoya
Takabo
Captive-born
Captive-born
Captive-born
Captive-born
Captive-born
Captive-born
Captive-born
Captive-born
Wild-born
Wild-born
Wild-born
Wild-born
Wild-born
B
Bamboo
Burlap sack
Straw
Towel
Tool-using
Banana-access test
Bamboo climbing
Am. J. Primatol.
632 / Morimura and Mori
consistently revealed an identical tendency: the skills
of Group B subjects were better than those of Group
A subjects.
The results of the two one-trial tasks were
consistent with the earlier findings that the skill of
wild-born subjects (Group B) is better than those of
captive-born subjects (Group A). Meanwhile, novelty
possibly affects material use by captive chimpanzees
[Bloomsmith et al., 2006]. No subject used a towel as
bedding material. The subjects’ experience with
various objects had been limited through most of
their lives. In addition, the one-trial task under
unusual situations diminished the task-solving ability in subjects of Group A. However, subjects of
Group B used unfamiliar objects as bedding material
and showed better performance in the two tasks than
Group A subjects under the unusual situation.
Subjects of Group B were more adaptive than
subjects of Group A, irrespective of the familiarity
of material and experimental situations.
The same group difference in solving a task
emerged in the banana-access test. The behavioral
difference between two groups in employing the
strategy of bamboo climbing was not explainable
simply by their physical ability and their experience
in practicing the task. The physical abilities of
subjects of the two groups were similar, indicating
similarity in the banana consumption overall and
similarity in walking. Among the seven subjects that
used bamboo, banana consumption by climbing a
bamboo pillar was not different between the two
groups. Furthermore, no evidence suggested that the
experience with the repetition of the test in the social
setting facilitated climbing the bamboo pillar. Consequently, the results show that the pillar-climbing
ability had already been acquired among subjects.
The same behavioral tendencies of the two groups
were reconfirmed in the sophisticated strategy of
sequential gathering in the task.
Age and differences of origin of the two groups are
possible factors influencing the group difference. The
effect of origin (early rearing condition) on the group
difference was not examined independently of age,
because captive-born individuals are generally the
offspring of wild-born individuals. The studies of
infant and juvenile chimpanzees (2–4 years old)
revealed that tool use and communication skills
became more flexible and sophisticated with age [Bard
& Russell, 1999; Tomasello et al., 1994]. In contrast,
old chimpanzees (30–40 years old) showed less
aggressive behavior and object manipulation than
younger chimpanzees (11–20 years old) [Baker,
2000]. Adult chimpanzees become less capable of daily
life behaviors with age. Results of this study show that
behavioral differences with age arising from behavioral development were insufficient to explain the group
difference: the older subjects (Group B) of 27.2 years,
on average, showed better skills in solving the tasks
than younger subjects (Group A) of 18.9 years.
Am. J. Primatol.
Therefore, their experiences, specifically their
different early rearing conditions––mother rearing
in the wild and mother and human rearing in
captivity––might provide a simpler explanation for
the group differences that were observed consistently. Results of this study underscored the adaptive and sophisticated skills of wild-born
chimpanzees in problem-solving tasks. Wild-born
chimpanzees (Group B) used various objects with
several alternatives for solving tasks efficiently, but
captive-born chimpanzees (Group A) had fewer
options for solving the tasks, and performed inefficiently. The results suggest that behavioral differences, according to the different rearing condition in
the subjects’ first few years of life, were manifested
not only in the behavioral repertoire of skills that
they experienced and acquired, but also in the
exertion of acquired behaviors in problem-solving,
which is associated with underlying cognitive processes. The result implies that wild-born chimpanzees understand and utilize living spaces differently
from captive-born chimpanzees. That cognitive difference [de Waal & Aureli, 1996] might affect bed
building, tool use, maternal competence, and social
communication skills throughout the life of captiveborn chimpanzees. Some physical and social deficits
of captive-born adult chimpanzees might arise from
the execution of behavioral repertoires that are
acquired early in a chimpanzee’s life. Meanwhile,
the higher-order intelligence of chimpanzees is
apparently sufficient to compensate for the negative
effects of early rearing conditions to some degree.
The adaptive skills of two captive-born chimpanzees
in the banana-access test suggest the flexibility of
chimpanzee intelligence and the importance of
environmental enrichment for the care of captive
chimpanzees, as described by Bloomsmith et al.
[2006]. Environmental enrichment programs should
take rearing conditions into consideration, especially
for restrictively reared chimpanzees, so that less
skilled chimpanzees have plenty of time to become
accustomed to the program in a better way through
the experience of problem-solving.
Further study is necessary to examine the
effects of early rearing conditions on captive chimpanzee behavior in a large sample, including both
sexes: this study investigated only 13 males at the
CSU. Mother-reared and nursery-reared individuals
of captive-born chimpanzees might differ in their
execution of acquired behavior [e.g. Baker et al.,
2000; Brent et al., 1995]. Better understanding of the
effects of early rearing conditions on captive chimpanzees’ behavior in later life is necessary for
alleviating the effects of rearing conditions and for
improving the quality of life of captive-born, especially human-reared and nursery-reared chimpanzees. These efforts and results are expected to
contribute greatly to establishing sustainable captive
populations of chimpanzees.
Problem-Solving Skill in Chimpanzees / 633
ACKNOWLEDGMENTS
This research was financially supported by the
2008 IPS Captive Care Grant to Naruki Morimura.
Thanks to Masaki Tomonaga, Susana Carvalho, and
anonymous reviewers for their insightful comments
related to an earlier version of the article. We also
thank the staff members of the Department of
Welfare and Longevity in the Wildlife Research
Center, Kyoto University, and the Chimpanzee
Sanctuary Uto for caring for the chimpanzees. All
animal care and handling conformed to the Guide for
the Care and Use of Great Apes of CSU. The
experiments were performed with CSU approval.
The guide is compiled with the ethical policy of Primate
Research Institute, Kyoto University, ASP Principles for the Ethical Treatment of nonhuman
Primates, and domestic laws on welfare and management of captive animals.
REFERENCES
Baker KC. 2000. Advanced age influences chimpanzee behavior in small social groups. Zoo Biology 19:111–119.
Baker KC, Seres M, Aureli F, de Waal FBM. 2000. Evaluating
social enrichment of chimpanzees: injury risks under three
housing conditions. American Journal of Primatology
51:161–175.
Bard KA, Russell CL. 1999. Evolutionary foundations of
imitation: social, cognitive and developmental aspects of
imitative processes in non-human primates. In: Nadel J,
Butterworth G, editors. Imitation in infancy. New York:
Cambridge University Press. p 89–123.
Bloomsmith MA, Baker KC, Ross SR, Lambeth SP. 2006. Early
rearing conditions and captive chimpanzee behavior: some
surprising findings. In: Sackett GP, Ruppenthal GC,
Elias K, editors. Nursery rearing of nonhuman primates in
the 21st century. New York: Springer. p 289–312.
Brent L. 2001. Behavior and environmental enrichment of
individually housed chimpanzees. In: Brent L, editor. The
care and management of captive chimpanzees. San Antonio:
American Society of Primatologists. p 147–171.
Brent L, Bloomsmith MA, Fisher SD. 1995. Factors determining tool-using ability in two captive chimpanzee (Pan
troglodytes) colonies. Primates 36:265–274.
Brent L, Williams-Blangero S, Stone AM. 1996. Evaluation of
the chimpanzee breeding program at the Southwest
Foundation for Biomedical Research. Laboratory Animal
Science 46:405–409.
de Waal FBM, Aureli F. 1996. Consolation, reconciliation, and
possible cognitive difference between macaques and chimpanzees. In: Russon AE, Bard KA, Parker ST, editors.
Reaching into thought: the minds of the great apes.
New York: Cambridge University Press. p 80–110.
Gluck JP, Harlow HF, Schiltz KA. 1973. Differential effect of
early enrichment and deprivation on learning in the rhesus
monkey (Macaca mulatta). Journal of Comparative and
Physiological Psychology 84:598–604.
Lichstein L, Sackett GP. 1971. Reactions by differentially
raised rhesus monkeys to noxious stimulation. Developmental Psychobiology 4:339–352.
Menzel EW, Davenport RK, Rogers CHM. 1970. The development of tool using in wild-born and restriction-reared
chimpanzees. Folia Primatologica 12:273–283.
Novak MA, Sackett GP. 2006. The effects of rearing
experiences: the early years. In: Sackett GP, Ruppenthal GC,
Elias K, editors. Nursery rearing of nonhuman primates in the
21st century. New York: Springer. p 5–19.
Pruetz JDE, McGrew WC. 2001. What does a chimpanzee
need? Using natural behavior to guide the care and
management of captive populations. In: Brent L, editor.
The care and management of captive chimpanzees. San
Antonio: American Society of Primatologists. p 17–37.
R Development Core Team. 2007. R: a language and environment for statistical computing. Vienna, Austria: R Foundation for Statistical Computing. Available from: URL http://
www.R-project.org
Tomasello M, Call J, Nagell K, Olguin R, Carpenter M.
1994. The learning and use of gestural signals by
young chimpanzees: a trans-generational study. Primates
35:137–154.
Turner CH, Davenport Jr RK, Rogers CM. 1969. The effect
of early deprivation on the social behavior of adolescent chimpanzees. American Journal of Psychiatry 125:
1531–1536.
Videan EN. 2006. Bed-building in captive chimpanzees (Pan
troglodytes): the importance of early rearing. American
Journal of Primatology 68:745–751.
Am. J. Primatol.
Документ
Категория
Без категории
Просмотров
0
Размер файла
95 Кб
Теги
effect, pan, problems, chimpanzee, malen, skills, conditions, troglodytes, rearing, solving, early, captive
1/--страниц
Пожаловаться на содержимое документа