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Effects of group composition on agonistic behavior of captive pigtail macaques Macaca nemestrina.

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Effects of Group Composition on Agonistic Behavior of
Captive Pigtail Macaques, Macaca nemestrina
J. DAZEY, K. KUYK, hi. OSWALD, J MARTENSON
AND J. E R W I N ~
Aegionul Primate Researrh Center Field Station, University of Wmhington,
Medical Lakc, Washington 9902%
KEY WORDS Pigtail macaque . Macaca nemestrina . Agonistic behavior * Aggression . Control role.
ABSTRACT
We surveyed agonistic behaviors of 20 captive groups of pigtail
macaques fMacaca nemestrina) housed under identical spatial conditions. Fifteen
groups contained one male each; the other five groups contained no adult males.
Groups included six to twelve adult females, some of which had infants with them.
We found no relationship between social density of groups and incidence of
agonistic behavior, but significantly more contact aggression (grab, hit, push, bite)
and noncontact aggression (chase, open-mouth “threat,” bark vocalization) occurred among females in groups containing no males than in those containing one
male each. Apparently, males played an important role in the inhibition of intragroup conflict.We also found that females in groups containing males exhibited
less noncontact aggression if infants were present than if no infants resided in their
groups. Thus, competition of females over infants must not have been an important
constituent of intragroup conflict under the conditions of this survey.
Destructive violence, observed in freeranging primates, is frequently intensified
under captive conditions (Rowell, ’67).
Nagel and Kummer (’74) suggested the following reasons for higher rates of agonistic
behavior among captive groups of cercopithecoid primates: (A) Social factors
such as competition over females, conflict
over infants, and disturbance of social
order, and (A) Ecological factors such as
competition over food or space, absence of
cover, excess time to engage in social behavior (time spent foraging by nonprovisioned animals), reduction of ecological
functions of alpha males, and incompatible
composition of groups.
Maintenance and breeding of nonhuman
primates in captivity has become vital to
assure a supply of research subjects for
domestic biomedical use and to avoid further depletion of wild populations; yet, little research on the effects of captive conditions on the behavior and physiology of
AM. J , PHYS. ANTHROP., 46: 73-76.
nonhuman primates has been reported,
and trauma sustained in aggressive interactions continues to be a problem in captive
groups. We instituted a series of research
projects designed to assess the factors contributing to violence and its control in captive groups of pigtail macaques to find
ways of minimizing the destructive consequences of aggression. While our primary
goal is increased efficiency and self-sufficiency in primate production, we also anticipate finding useful analogues of human
aggressive motivation. In the project reported here we studied influences of group
’ Ihib research was supported b y NIHiCSPHS grant
RHO0166 to the Regional Primate Research Center at University of‘Washington and by an intramural grant from the Fund
for Instructional Developmrnt and Innovation, University of
Washington. J , Erwin r w r i v e d partial siipport under
NICBHD-08633 during the period in which this project WRY
done. l h e authors gratefully acknowledge the cuoperation or
the staff‘of the Primate Field Station.
* Rrquestt\ for reprints of this paper should b e addressed to
J. Erwin, c/o Regional Primate Heseai-ch Center, Univrrsity of
Washington, Seattle, Washington 98195.
73
74
DAZE”, KUYK, OSWALD, MAHTEMON AKD ERWIN
composition (primarily the presence or absence of adult males) on the expression of
agonistic behavior by adult females.
METHODS
Subjects
The subjects for this survey were 203
pigtail macaques (15 adult males, 166 adult
females, and 22 infants less than six months
old) housed in 20 groups at the Regional
Primate Research Center Field Station,
Medical Lake, Washington. Fifteen groups
contained one male each while five groups
included no adult males. Ten groups contained no infants; the other groups contained one to three infants. The number of
adult females per group ranged from 6 to
12.
All groups were housed indoors under
identical spatial conditions. Each group
had access to two adjoining rooms with access between rooms provided by a small
shuttle door. A detailed description of the
facility is contained in Blakley et al. (‘721.
Procedure
Two pairs of experienced observers
recorded absolute frequencies of agonistic
encounters in the groups. We measured the
incidence of contact aggression (grab,
push, hit, bite), non-contact aggression
(chase, openmouth “threat,” bark vocalization), and fear/submission (grimace,
screech, crouch). Agonistic encounters
were identified according to perpetrator
and recipient: adult male, adult female, or
infant. Two of us observed each group for
15minutes, one watching each room of the
suite; then the other pair did so. We balanced the order of observation and did not
give the second pair of observers access to
the data gathered by the first pair; thus,
the survey included a blind replication.
We evaluated differences between
male-present and male-absent conditions
and infant-present and infant-absent conditions using the Mann-Whitney U test for
differences between means of unequalsized samples.
RESULTS
As table 1 shows, females exhibited significantly less contact aggression, non-contact aggression, and total agonistic behavior toward each other in groups containing
one male than in those containing no males.
The differences were statistically significant for the initial session and the replication. Total non-contact aggression in
groups containing males was significantly
less frequent if infants were present (mean
= 0.554; S.D. = 0.519) than if no infants
were present (mean = 1.070; S.D. =
0.587) (Mann-Whitney U = 5; P < 0.01).
Social density (number of animals per
group) exerted no detectable influence on
agonistic behavior. Fear/submission behaviors occurred infrequently; we detected no
relationship between group composition
and any behavior involving males or infants.
DISCUSSION
The influence of males on agonistic interactions was the most consistent effect
we detected in this survey. Bernstein (’64)
and Smith (’74) have documented active
interference of male macaques in intragroup agonistic encounters. Erwin (’76)
and Tokuda and Jensen (’68)have reported
that short-term removal of males from
groups of pigtail monkeys resulted in increased aggression among females, and
reinstatement of males restored peace
among females. The survey reported here
and a smaller one done previously by
Sackett et al. (’75)provides clear evidence
that the mere presence of an adult male in
a group of female pigtail monkeys inhibits
aggressivity. We noted that most interference by males was in the form of very
mild “threatened” aggression, often no
more than a brief stare toward the perpetrating female. The incidence and effcctiveness of such interference varied inversely with the distance between the male
and the interacting females. Most attacks
that occurred near the male consisted of a
(0-11-3)
(0- 9-11
(0- 9-01
(0- 8-1)
(0- 6-01
(0-43-5)
1- 12- 3)
1- 10- 3)
1- 9- 3)
1- 9- 2)
1- 9- 2)
1- 9- 0 )
1- 8- 0)
1- 8- 0)
1- 8- 0)
1- 8- 0)
1- 7- 3)
1- 7- 0)
1- 7- 0)
1- 6- 1)
1- 6- 0)
(15-123-17)
(
(
(
(
(
(
(
(
(
(
(
(
(
(
(
Males-fernalea
inf.
Composition
Total
Mean
S.D.
Differences between harern
and all-female groups
.Mariri-Whitriey U
Probability
x
XIX
XVI
XVII
XVlII
(h u p a
1V
V
\'I
VII
\'Ill
IX
X
XI
XI1
XI11
XlV
XV
Total
Mean
S.D.
All -female
111
I
11
Harem
Groups
Gronp No.
I
< 0.05
11
0.273
0.556
1.667
2.125
0.333
4.954
0.991
0.849
0.250
0.500
0.000
0.111
0.222
0.778
0.125
0.125
0.125
0.500
0.286
1.000
0.000
0.500
0.333
4.855
0.324
0.286
1st 011s.
10
< 0,05
9
< 0.05
1.182
1.000
4.000
3.500
0.500
10.182
2.036
I594
0.346
0.667
0.500
0.222
0.111
0.889
0.889
0.375
0.125
0.37s
1.125
0.286
1.000
0.143
0.833
0.333
7.873
0.525
Total
0.909
0.444
2.333
1.375
0.167
3.228
1.046
0.854
0.417
0.000
0.222
0.000
0.667
0.111
0.250
0.000
0.250
0.625
0.000
0.000
0.143
0.333
0.000
3.018
0.201
0.227
2nd obs.
Contac? aggression
9
< 0.05
0.273
2.000
2.889
1.250
2 500
8.912
1.782
1.043
0.250
0.200
0.444
0.333
0.222
1.111
0.125
0.500
0.625
0.000
0.143
1.143
0.286
0.667
1.167
7.216
0.481
0.387
1st ohs.
Otis.
5.5
< 0.01
1.364
2.556
2.778
3.000
0.333
10.031
2.006
1.129
0.083
0 200
0.222
0.111
0.000
0.333
1.250
0.000
1.375
0.500
0.000
0.143
0.000
1.000
0.000
5.217
0.348
0.473
2nd
2
< 0.01
5.667
4.250
2.833
18.942
3.788
1.571
4.556
1.636
0.333
0.400
0.667
0.444
0.222
1.444
1.375
0.500
2.000
0.500
0.143
1.286
0.286
1.667
1.167
12.434
0.829
0.599
Total
Nnrr-contact aggre\\ion
ns.
n.s.
0.091
0.333
0.333
0.000
0.000
0.737
0.151
0.170
0.000
0.167
0.000
0.778
0.052
0.106
0.ODO
0.000
0.000
0.000
0.000
0.375
0.125
0.000
0.000
0.111
0.000
0.000
2nd obs.
0.000
0.111
0.000
0.000
0.000
0.111
0.022
0.050
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.125
0.000
0.000
0.000
0.000
0.000
0.125
0.008
0.032
1st olis.
Ft.ar/srd)mission
Agoriistic hehucior amongfemcrle Macaca rierncstriria in captive groups (frequency per cupitu)
'I'r\HL.E
11,s.
-
0.091
0.444
0.333
0.000
0.000
0.868
0.174
0.203
0.000
0.000
0.111
0.000
0.000
0.000
0.000
0.375
0.125
0.125
0.000
0.000
0.000
0.167
0.000
0.903
0.060
0.106
Total
0
< 0.01
2.909
6.000
10.000
7.750
3.333
29.992
5.998
2.989
1.000
0.900
1.000
0.356
1.11I
2.333
1.7.50
1.000
2.300
1.750
0.429
2.000
0.429
2.667
I .so0
20.925
1.395
0.742
Total
agonistic
76
DAZEY, KUYK, OSW.\LD, MAKTENSOS AND EKWlN
single aggressive act, usually a grab or hite;
we seldom saw any reciprocation. Thus, it
appears that remaining near a male allows
females the freedom to attack other females briefly without fear of retaliation
while affording them protection from sustained attacks by other feniales. Under the
conditions of this survey, feniales spent
most of their time in the same room a s the
male even though they had access to an
adjoining room. We found in an earlier
study that less aggression occurred among
females confined to one room than when
given access to both rooms of their suites
(Anderson et al., '76). Apparently; aggression is inhibited more effectively undcr
conditions of forced proximity than under
relatively less crowded conditions.
One of the sources of intragroup conflict
suggested by Nagel and Kummer ('74) was
competition over infants. Under the conditions of this survey, this was clearly not an
important contributor to intragroup conflict because the only general effect of
presence of infants in groups was reduced
non-contact aggression. All infants involved in this survey were less than sixmonths-old, and no juvenile or adolescent
animals were present in groups. While
females are retentive and protective of
young infants, infants exhibit little social
involvement during their fist half-year
relative to their second half-year of life (cf.
Jensen et al., '68; Kuyk et al., '76). Our
failure to find a relationship between social
density (number of animals per group) and
aggression was rather surprising in view of
previous evidence (Anderson et al., '76;
Erwin and Erwin, '76) that contact aggression was positively related to social density.
Research on agonistic behavior of captive groups of nonhuman primates can be
of practical value by providing evidence
helpful in establishing and maintaining
self-sufficient domestic colonies for the
production of biomedical subjects, but it
can also generate hypotheses useful in the
analysis of social organization in groups.
Elucidation of the dynamics of social processes in natural groups of primates contributes substantially to the understanding
of primate evolution.
LITERATURE CITED
Anderson, B., N. Erwin, I).Flynn, I,. Lewis and J. Erwin 1976 Effects of short-term crowding on aggression in captive groups of' pigtail monkey.;
(LMacac.a nemestrina). 8ggrt:ssive Behavior, in
press.
Bernstein, I.
1964 Group social pattcms a s
influenced b y removal and later reiritroduction o f
the dominant male rhesus. Psychol. Rep., 14: 3-10.
Rlakley, G.. W. Morton arid 0.Sriiith 1972 Husbandry and breeding of &fucacanemestrina. In: Medicnl
Primatology 1972, Part I. S. Karger, Basel, pp.
61-72.
Erwin, J. 1976 Aggressive lichavior of captive pigtail
macaques: spatial conditions a n d social cmtrolh.
Lahoratory Primatc. Newsletter, 15 (2): 1-10
Eruin, N.. and J . Erwin 1976 Social density and aggression in captivc. groups of pigtail Inonkey
(macacn nemesfrina). Applied Animal Ethology, in
press.
Jcnsen, G., R. Bobliitt and B. Gordon 1968 Sex differences in the development of independence of infant
monkeys. Behaviour, 30: 1-14.
Kriyk, K., J. Dazey and J. Erwin 1976 Play patterns of
pigtail nionkey infants: effects of age and peer presence. Journal of Biological Psychology, in press.
Nagel, U., arid H. Krimmer 1974 Variation in cercopithecoid aggressive behavior. In: Primate aggrcssion, Territoriality. and Xcnoptiot)ia: a Coniparative Perspective. R. Holloway, ecl. Academic
Press. New York, pp. 159-184.
Howelli T. 1967 4 quantitative cornparison of t h e b e haviour of a wild and a caged 1)aI)oongroup. ,hima1
Behaviour, 15: 499-509.
Sackett, D., M. Oswald and J. Erwin 1975 Aggression
among captive female pigtail monkeys in all-fefziale
and harem groups. Journal of' Iliological Psychology,
17 (21: 17-20.
Smith, E. 1973 A fiirthcr description of the control
role in pigtail macaques, Macnca raemestrha. Primates, 14: 413-419.
Tokuda, K., and G. Jellsen 1968 ' I l ~ eleader's role in
controlling aggressive hehavior in a monkey- group.
Primates, 9: 319-322.
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