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All content in this area was uploaded by Joseph Tangah on Sep 17, 2021
Content may be subject to copyright.
Content uploaded by Joseph Tangah
Author content
All content in this area was uploaded by Joseph Tangah on Sep 17, 2021
Content may be subject to copyright.
ISSN 1880-7682
Volume 11, No. 3 December 2013
ISME/GLOMIS Electronic Journal (ISSN 1880-7682) is published by International Society for Mangrove Ecosystems (ISME). Available on-line
at http://www.glomis.com. Headquarters:c/o Faculty of Agriculture, University of theRyukyus, 1 Senbaru, Nishihara, Okinawa, 903-0129 Japan. 8
ISME/GLOMIS Electronic Journal
An electronic journal dedicated to enhance public awareness
on the importance of mangrove ecosystems
____________________________________________________________________________________
A note on the agonistic behaviour of proboscis
monkeys at Labuk Bay, Sandakan, Sabah
Introduction
Social animals display various behaviours to maintain
social structure and spacing of group members. In
agonistic behaviour, one animal becomes aggressive or
attacks another animal, which returns the aggression or
submits (Miller & Harley, 2005). Besides actual
aggression, agonistic behaviour includes threat display,
retreat, placating aggressors and conciliation. Agonistic
behaviour is seen in many animal species because
resources including food, shelter, mates and space are
often limited. In many species, the males vent much of
their aggression in the form of threat displays warning
other males of an intention to defend an area or territory.
Agonistic behaviour is important in the maintenance of
territories and dominance hierarchies. In proboscis
monkeys, high-intensity agonistic displays of slapping,
chasing, biting are rare (Yeager, 1992). Low intensity
agonistic displays of vocalization, leaping and branch
shaking, and penile erection with open-mouth displays,
are more frequent. Early morning displays by the adult
males are some behavioural activities to ensure temporal
avoidance between groups.
The capability of the Labuk Bay Proboscis Monkey
Sanctuary (LBPMS) in successfully conserving and
promoting ecotourism on proboscis monkeys in an
isolated mangrove forest prompted this study. The initial
effort of total conversion of mangroves to oil palm estate
was halted due to the existence of wild proboscis
monkey populations. It was reported that the proboscis
monkeys in the remaining patches of mangrove forest
displayed aggressive behaviour due to the lost of
foraging area in their natural habitat. Furthermore, the
populations in LBPMS are wild and difficult to relocate
to nearby mangrove forest reserves. These problems
have forced the management of LBPMS to conserve the
remaining mangrove forest fragment as habitat and
foraging area for the proboscis monkeys, and to provide
pancakes as supplementary feeds.
Study site
In this study, the behaviour of proboscis monkey
populations in Zones A and B of LBPMS (N 5º56’14.9”;
E 117º47’ 44.5”) was monitored. Located ~48 km west
of Sandakan in Sabah, the mangrove forest proboscis
monkey sanctuary (263 ha) is surrounded by tracts of oil
palm plantations except the northern part, which borders
the Sulu Sea (Fig. 1). Kampung Samawang, the nearest
village, is located ~3 km southwest of LBPMS and the
topography is relatively flat (0.5í2.0 m asl).
Methods
Based on the scan sampling method of Altmann (1974),
direct observations on the agonistic behaviour of
proboscis monkey populations at LBPMS were made
from October 2008 to July 2009. Sightings were made
with binoculars and recorded using Canon video camera.
To determine whether the focal groups of proboscis
monkeys were territorial, analysis was conducted using
the territoriality formula D=d/¥(4A/ʌ)whereD=index
of defensibility, d = daily path length (km) and A =
home range area (km2) (Mitani & Rodman, (1979).
When using this formula to determine the territorial
behaviour of an animal group, if the value of D1, the
group is expected to be territorial. Values < 1 reflect
non-territorial behaviour. The frequency of agonistic
behaviour and the amount of pancakes consumed per
individual monkey (kg/month) was correlated.
Results and discussion
From 2004 to 2009, the proboscis monkey populations in
LBPMS increased from 89 to 148 individuals, indicating
that the proboscis monkeys are able to survive in isolated
mangroves of the sanctuary. The territorial behaviour of
all focal groups indicated their ability to defend occupied
areas. The groups confine and defend the mangrove
forests surrounding the feeding platforms.
In this study, the agonistic behaviour of proboscis
monkeys is 2.85% (n= 1,021) of their total activity time
based on ~35,900 observations made mostly at the
feeding platforms when the animals are feeding on
pancakes. The average amount of pancakes consumed
per day per focal group is shown in Table 1. In Zone A,
the amount consumed per day per focal group ranged
from 2.29í3.55 kg with an individual consuming
210í230 g. In Zone B, the group and individual daily
consumption was 1.11í3.13 kg and 130í300 g,
respectively.
The overlapping movement of proboscis monkeys in
LBPMS suggests the existence of territorial behaviour
among groups of proboscis monkeys as indicated by the
high index of defensibility value (D). In this study, the D
values of all focal groups were more than > 3, with KK
(D= 4.56) and Owen (D= 4.61) being the most
territorial for the one male units (OMU) and all male
units (AMU), respectively (Table 2).
ISSN 1880-7682
Volume 11, No. 3 December 2013
ISME/GLOMIS Electronic Journal (ISSN 1880-7682) is published by International Society for Mangrove Ecosystems (ISME). Available on-line
at http://www.glomis.com. Headquarters:c/o Faculty of Agriculture, University of theRyukyus, 1 Senbaru, Nishihara, Okinawa, 903-0129 Japan. 9
In this study, the amount of pancakes consumed per individual based on seven focal groups was negatively
correlated to frequency of agonistic behaviour with P=0.29andr=í0.43 (Fig. 2). This indicated that the
frequency of agonistic behaviour of proboscis monkeys at LBPMS decreased with increasing amounts of
pancakes consumed per individual.
Although agonistic behaviour of the proboscis monkeys in LBPMS is a minor activity, the percentage of time
allocated for aggression was higher than the wild populations such as those at Sukau in Kinabatangan. In Sukau,
young leaves are available in abundance throughout the year and this may reduce the aggressive behaviour of the
wild proboscis monkeys. In this study, most of the agonism was recorded during feeding time at the respective
feeding platforms at LBPMS. The amount of pancake contributed to the aggressive behaviour of the monkeys,
whereby an increase in pancake intake reduced aggression. The different groups frequently used the same area,
slept on the same trees, foraged from the same mangrove plants, and travelled along the same ground and arboreal
routes.
In LBPMS, the territorial behaviour of proboscis monkeys was related to aggression, suggesting that their
ranging areas were overlapping and aggravated bythe feeding programme. With only two focal groups, there was
minimal range overlapping in Zone A. There was ample space for both groups to roam freely. On the other hand,
range separation was not possible for the five focal groups in Zone B and their movement pattern was highly
overlapping. All the focal groups in Zone B were highly territorial as reflected by their high Dvalues of 3.
In conclusion, one should not generalise that proboscis monkeys are shy and non-territorial animals. Under
stressful habitat settings such as the isolated mangroves of LBPMS, agonism in the form of aggressive behaviour
may prevail among proboscis monkeys (Fig. 3).
Fig. 1 Map of LBPMS showing the location of the study area (Zones A and B)
Acknowledgments
I am thankful to Datuk Sam Mannan (Director of Sabah Forestry Department) and Mr. Fidelis Edwin Bajau
(Deputy Director of Development) for their encouragement and continuous support, and to Datuk Ambrose John
Juin for allowing me to carry out the study at LBPMS. My gratitude goes to Dr. H.T. Chan for his constructive
comments on the manuscript, and to Mr. Jamiss Aribin and Mr. Dauni Seligi for helping in the collection of field
data.
Z
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A
Z
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B
ISSN 1880-7682
Volume 11, No. 3 December 2013
ISME/GLOMIS Electronic Journal (ISSN 1880-7682) is published by International Society for Mangrove Ecosystems (ISME). Available on-line
at http://www.glomis.com. Headquarters:c/o Faculty of Agriculture, University of theRyukyus, 1 Senbaru, Nishihara, Okinawa, 903-0129 Japan. 10
Fig. 2 The correlation pattern of the frequency of agonistic behaviour of proboscis monkeys vs. the amount
of pancakes consumed per individual (kg/month)
Fig. 3 Agonistic displays by an all male unit (AMU) in LBPMS
ISSN 1880-7682
Volume 11, No. 3 December 2013
ISME/GLOMIS Electronic Journal (ISSN 1880-7682) is published by International Society for Mangrove Ecosystems (ISME). Available on-line
at http://www.glomis.com. Headquarters:c/o Faculty of Agriculture, University of theRyukyus, 1 Senbaru, Nishihara, Okinawa, 903-0129 Japan. 11
Table 1 Average amount of pancakes consumed by focal groups
kg/group/day kg/day/monkeyZone Group ID Mean ± SD Mean ± SD Mann-Whitney
U test, pKruskal
Wallis test, p
A John 3.55 ± 0.54 0.23 ± 0.08
Jonathan 2.29 ± 0.35 0.21 ± 0.03 <0.05
<0.05
B KK 3.13 ± 0.35 0.13 ± 0.03
Ronaldo 2.10 ± 0.60 0.19 ± 0.06
Rivaldo 1.37 ± 0.25 0.26 ± 0.11
KC 1.11 ± 0.53 0.21 ± 0.07
Owen 1.56 ± 0.36 0.30 ± 0.15
<0.01
<0.01
<0.01
<0.01
<0.01
Table 2 Index of defensibility (D) of various focal groups of proboscis monkeys
Zone Group type Group ID D
A OMU John 3.91
A OMU Jonathan 4.12
B OMU KK 4.56
B OMU Ronaldo 4.38
B OMU Rivaldo 3.95
B AMU KC 3.67
B AMU Owen 4.61
OMU = one male unit, AMU = allmale unit, ID = identity and D= index of defensibility
References
Altmann, J., 1974. Observational study of behaviour: Sampling methods. Behaviour, 69, 227í267.
Miller, S.A. & Harley, J.B., 2005. Chapter 34 Animal behaviour. In: Zoology. McGraw-Hill Higher Education.
Mitani, J.C. & Rodman, P.S., 1979. Territoriality: The relationship of ranging patterns and home range size to
defensibility, with an analysis of territoriality among primate species. Behavioral Ecology and Sociobiology,5,
241í251.
Yeager, C.P., 1992. Proboscis monkey (Nasalis larvatus) social organization: Nature and possible functions of
intergroup patterns of association. American Journal of Primatology, 26(2), 133í137.
Joseph Tangah
Head of Forest Conservation, Forest Research Centre,
Sabah Forestry Department, Sandakan, Sabah
E-mail: Joseph.Tangah@sabah.gov.my
