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Volume 1 • Issue 2 • 1000e107
J Primatol
ISSN: JPMT, an open access journal
Research Article Open Access
Dittus, J Primatol 2012, 1:2
http://dx.doi.org/10.4172/jpmt.1000e107
Editorial Open Access
Primatology
An Online Forum for Exchanging Ideas for Dealing with Issues of Pest
Monkeys
Wolfgang Dittus1,2*
1Conservation Ecology Center, Smithsonian Conservation Biology Institute, Washington, DC, USA
2Institute of Fundamental Studies, Sri Lanka
*Corresponding author: Wolfgang Dittus, Ph.D., Conservation Ecology Center,
Smithsonian Conservation Biology Institute, Washington, DC, USA, E-mail:
dittus@sltnet.lk
Received April 18, 2012; Accepted April 20, 2012; Published April 22, 2012
Citation: Dittus W (2012) An Online Forum for Exchanging Ideas for Dealing with
Issues of Pest Monkeys. J Primatol 1:e106. doi:10.4172/jpmt.1000e106
Copyright: © 2012 Dittus W. This is an open-access article distributed under the
terms of the Creative Commons Attribution License, which permits unrestricted
use, distribution, and reproduction in any medium, provided the original author and
source are credited.
Habitat countries for nonhuman primates worldwide have wit-
nessed increasing degrees of conict between humans and feral mon-
keys over the last several decades. Primatologists and conservation
managers are oen at a loss of how best to deal with the issue because,
more oen than not, the conict is owed to, or exacerbated by, inap-
propriate human practices rather than to monkey behavior, per se. Al-
though countries and the primate species involved dier, as do local
situations, there are basic elements common to most such conicts.
e practical solutions to nding workable approaches to reducing
human-monkey conict situations appear to be fairly straight forward
compared to the greater challenge of overcoming ingrained cultural
attitudes, inappropriate knee-jerk reactions by the public and authori-
ties, and misunderstanding among policy makers and their wildlife
management bureaucracies. It is hoped that this open access publisher
of the OMICS Publishing Group with its facilities for language transla-
tion, social networking and audio enhancement can serve as a useful
forum for informal information sharing about successful approaches
both in reducing human-monkey conicts and in implementing them
by way of wildlife managers.
Publications on human-monkey conicts appear to be rare com-
pared to local reports, word-of-mouth communications and media
clippings. My perspective in this editorial is based primarily on my four
decades of primate eld research in Sri Lanka and brief visits to other
countries in the region, discussions and conferences with colleagues
and managers. is consideration excludes the mindless mass killings
of wildlife and habitat destruction that occurs as a result of logging and
similar commercial operations in far too many tropical regions. I con-
ne myself to environmental contexts where nonhuman primates still
survive near humans such that conict between them can even occur.
Primates become pests for one reason only: they seek easy to obtain
food and water near human habitation. Macaques, baboons and gue-
nons (Sub-family Cercopithecinae) having more or less omnivorous
diets, and adventurous inclinations, are far more likely to adopt new
food types in human modied environments than are their more strict-
ly leaf-eating cousins of the Sub-family Colobinae. at is not to say
that some, like the hanuman or gray langur of the Indian subcontinent
and Sri Lanka cannot become pests: they do. With persistent and oen
insistent feeding by humans these less likely candidates for commen-
salism too; have been converted to the easy life of raiding. You might
ask what harm can be done by donating human food to monkeys, it is
aer-all motivated by a benign and well-intentioned sentiment? e
sentiment, of course is a salvation for monkeys in countries with strong
Hindu and Buddhist traditions. e problem arises because articial
feeding leads to changes in monkey behavior and population ecology
and to an overpopulation of tame, sometimes aggressive, monkeys near
human habitation.
In natural undisturbed forest or savannah primate habitats, in
which primates evolved and to which they are well adapted, the num-
bers of primates in any population are kept in check by the availability
of natural food sources and water. Although disease and predation may
have a temporary depressive eect on local population numbers, over
the long term, zero-population growth is the rule for primate popu-
lations in stable environments, or, their numbers wax and wane with
changes in environmental quality. e eect of crops, garbage and pur-
poseful feeding of monkeys is to release the natural cap on population
growth. An empirical example of this is clear from our studies at Po-
lonnaruwa, Sri Lanka, where two groups of toque macaques (Macaca
sinica) with overlapping home ranges had dierent degrees of access to
human refuse. Over a thirty-year period the group with less than 2%
garbage in their diet remained stable in size or actually declined slightly
in numbers, whereas the one with more than 30% of human food in
their diet increased exponentially, or 5 fold in number (Figure 1). e
pattern is common to all primate species where human food is acces-
sible to them. In towns, villages, tourist sites and temples, where food
refuse is oen disposed openly, monkeys are a common occurrence
and their numbers grow. At the same time, inappropriate human be-
havior, such as oering food to monkeys, converts them into aggressive
pests that raid property.
Dierent countries have applied dierent solutions to controlling
Number of toque macaques in relation to their diet
160
140
120
100
80
60
40
20
0
Number of macaques
1970 1975 1980 1985 1990 1995 2000
Year
>30% diet on food refuse
>98% natural diet
Figure 1: Contrasting the population growth of two neighboring groups of
toque macaques (Macaca sinica) at Polonnaruwa, Sri Lanka, that differs in the
degree of human food refuse in their diets, over a thirty year period.
Citation: Dittus W (2012) An Online Forum for Exchanging Ideas for Dealing with Issues of Pest Monkeys. J Primatol 1:e107. doi:10.4172/
jpmt.1000e107
Page 2 of 2
Volume 1 • Issue 2 • 1000e107
J Primatol
ISSN: JPMT, an open access journal
monkey numbers: killing, sterilization, and trans-locating. Culling is
not ethically or politically acceptable in some countries and is point-
less (see below). Sterilization of monkeys, either surgically or with hor-
monal implants, ought to target females, rather than males, as they are
the bottle-neck for birth rates. However, the procedures are laborious,
require well qualied personnel, are expensive and ultimately their ef-
fects are short-lived. e method has been applied with some success in
smaller populations, such as are found in Hong Kong, but it is imprac-
tical on a larger scale. Capturing and trans-locating pest monkeys into
rural or forested areas is a popular approach among many bureaucrats
because of its political, albeit deceptive, appeal. By themselves, none of
these methods are eective in the long-term in controlling pest mon-
keys because they address the symptom (too many monkeys) and ig-
nore the root cause of primate population growth. As long as monkeys
have access to human crops or food scraps monkey numbers will grow.
Sites where monkeys have been removed by culling or trans-locating
will be repopulated from neighboring monkey populations that are at-
tracted to the ecological void le by the removed monkeys. Transloca-
tion is particularly inappropriate on several counts: (a) monkeys are
injured and killed in the capture and transport and release process. (b)
If the site of release is a natural forest or protected area with resident
primates of the same species, the transferred newcomers clash in ter-
ritorial disputes with resident monkeys, the carrying capacity of the
habitat for that species is exceeded and monkeys are subject to mortal-
ity. (c) In areas of India and Sri Lanka, street-wise monkeys from towns
or tourist sites have been transported and released into rural areas with
the drastic result of aggressive town monkeys causing havoc in places
where, over millennia, villagers and local forest-dwelling monkeys had
lived more or less peacefully in mutual respect and exclusivity. Basi-
cally, problem monkeys from well-to-do townships are dumped into
rural communities having lesser political and economic clout. Trans-
locating monkeys should be banned on grounds of this sociopolitical
abuse of poor human communities alone. (d) Trans-locating monkeys
of one subspecies into the habitat of another undermine biodiversity
and cloud the genetic history of the species in scientic studies.
e solution lies not in controlling pest monkeys aer their num-
bers have already grown and developed aggressive attitudes towards
humans, but in preventing their numbers from growing in the rst
place. is is achieved best by implementing measures to prevent
monkeys from gaining access to human food. Limiting food and water
supplies reduces monkey numbers because it slows their birth rates,
delays their age of reproductive maturation and impacts their survival.
e importance of this basic biological principle and its application to
preventing monkey’s access to human foods has been recognized and
acted upon by several nations. In Singapore, for example, the deter-
rent for feeding monkeys can be a ne of $50,000 and a 6 months jail
term. Similar legislation has been adopted in many countries. But the
threat of nes alone merely may discourage some people; it needs to be
accompanied by other measures, such as the installation of monkey-
proof garbage disposals, safe-guarding of crops, and in particular, the
education of the public and wildlife authorities to adopt more eective
measures to prevent the build-up of large numbers of pest monkeys.
e challenge is particularly strong at the extremes of public senti-
ments towards monkeys: religious donations to monkeys as deities on
one hand, and unsympathetic eradication on the other. It is hoped that
a forum for the exchange of ideas on this topic may contribute to con-
servation and a reduction of human-monkey conict.