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An Online Forum for Exchanging Ideas for Dealing with Issues of Pest Monkeys

Volume 1 • Issue 2 • 1000e107
J Primatol
ISSN: JPMT, an open access journal
Research Article Open Access
Dittus, J Primatol 2012, 1:2
Editorial Open Access
An Online Forum for Exchanging Ideas for Dealing with Issues of Pest
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:
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 conict between humans and feral mon-
keys over the last several decades. Primatologists and conservation
managers are oen at a loss of how best to deal with the issue because,
more oen than not, the conict 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 dier, as do local
situations, there are basic elements common to most such conicts.
e practical solutions to nding workable approaches to reducing
human-monkey conict 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 conicts and in implementing them
by way of wildlife managers.
Publications on human-monkey conicts 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 conict 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 modied 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 oen
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
aer-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 articial
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 eect 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 eect 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 dierent 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 oen disposed openly, monkeys are a common occurrence
and their numbers grow. At the same time, inappropriate human be-
havior, such as oering food to monkeys, converts them into aggressive
pests that raid property.
Dierent countries have applied dierent solutions to controlling
Number of toque macaques in relation to their diet
Number of macaques
1970 1975 1980 1985 1990 1995 2000
>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/
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 qualied 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 eective 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 scientic studies.
e solution lies not in controlling pest monkeys aer 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 eective
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 conict.
... Countries endowed with natural habitats for NHPs, such as Japan, India, Sri Lanka or Singapore, have witnessed increasing degrees of conflict between humans and feral monkeys over the last several decades. 35 NHPs become pests when they seek to obtain food and water near human habitation. Artificial feeding leads to changes in monkey behavior, and in population ecology by causing overpopulation of relatively aggressive monkeys. ...
... On the one hand, killing a large number of animals is considered unethical according to the welfare regulation of several countries, while on the other hand sterilization and translocation practices are expensive and very laborious, because they require specialized personnel and long-term commitment. 35 To sum up, natural parks for primate experimentation may be beneficial from both a methodological and ethical perspective and in particular may (1) enhance scientific validity, by providing a more suitable animal model for the study of mental functions and psychiatric disorders that can be translated into effective therapies, (2) provide naturalistic wild-like environments for NHPs, and avoid their translocation to different countries, and (3) allow data collection that can benefit primate conservation, and help control of risks from human-animal interactions. ...
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In this paper, we emphasize the importance of studying the primate brain in cognitive neuroscience and suggest a new mind-set in primate experimentation within the boundaries of animal welfare regulations. Specifically, we list the advantages of investigating both genes and neural mechanisms and processes in the emergence of behavioral and cognitive functions, and propose the establishment of an open field of primate research. The latter may be conducted by implementing and harmonizing experimental practices with ethical guidelines that regulate (1) management of natural parks with free-moving populations of target nonhuman primates, (2) establishment of indoor-outdoor labs for both system genetics and neuroscience investigations, and (3) hotel space and technologies which remotely collect and dislocate information regarding primates geographically located elsewhere.
... Having lost its natural habitat to deforestation, it has readily adapted to eating human food discarded with garbage in urban areas. This habit has resulted in noticeable localised increases in macaque populations especially around tourist sites and other public places where food can be obtained from garbage dumps (Dittus 2012a(Dittus ,b, 2013b). In some of these areas the macaques are considered pests. ...
... This may be done with use of monkeyproof garbage bins, which should be emptied regularly and closely monitored from collection to disposal (Dittus 2012b;Mckinney 2015;Mendis & Dangolla 2016). It is important to enforce strict regulations to prevent feeding monkeys ( Singh et al. 2005;Dittus 2012a). It has been reported that even with signage and penalties imposed on people to stop feeding monkeys in public places, people continue to do so (Newsome & Rodger 2008;Hsu et al. 2009). ...
Full-text available
Human-monkey conflicts reached crisis proportions in Sri Lanka over the last 10 years due to extensive deforestation to promote rapid economic growth and agricultural expansion. This resulted in complaints from the public with demands for Sri Lanka’s Department of Wildlife Conservation (DWC) to solve the problem without delay. Caught between political pressure and public outcry, the DWC’s efforts to deal with the crisis gradually fell into disarray. To overcome this, the SPEARS Foundation--, offered to help the DWC to develop a strategic plan to deal with human-monkey conflicts. This plan was developed through a series of workshops and submitted to the Ministry of Sustainable Development and Wildlife in March 2016 for approval. During and after the development of the strategy, some of its key elements were implemented by the SPEARS Foundation. One of these elements was documenting details of human-monkey conflict from letters of complaint received by DWC. This information was used to initiate a series of field surveys to identify sites suitable for long-term protection of monkeys and other wildlife. When these areas are identified they would be designated as community conservation areas (CCAs), and managed by local stakeholders on a sustainable basis under the supervision of DWC. Establishing CCAs is a new paradigm for Sri Lanka to conserve wildlife while benefitting local communities. Its details were presented in the strategic plan submitted to the government. In this paper, we present the information obtained from the letters of complaint received by DWC and discuss its details. In subsequent reports, we will discuss the results of our field surveys to identify areas suitable for the establishment of CCAs.
... Damage of crops by the rhesus macaques is also reported fromthe different parts of India and the other countries (Saraswat et al. 2015, Dela 2011, Nahallage and Huffman 2013. Now a days, macaques are acting aggressively towards the people they attack people to grab food, snatch hand bags and the people are also acting aggressive in return towards them (Dittus 2012). ...
Full-text available
Conflicts between humans and monkeys are recognized among major issues related to human-wildlife conflict. Today, human-monkey conflict has garnered the global attention as over the years it has become a serious concern. The present study was done in the human dominated landscape of Najibabad forest division (NFD). The data were collected from 2015 to 2018. The study aimed to assess the damage caused by monkeys on human-society and crop fields. The study showed that biting humans, destroying orchards, crops and stealing household things are the major damages caused by rhesus macaques (Macaca mullata). Destruction of habitats, over-population, and improper disposal of wastes are the main causes of human-monkey conflict and the monkeys also face threat in such situations. Hostile attitude of people and transportation of trapped monkey to release them in forest causes injuries or even death of monkeys.
... Another benefit of this approach is related to those countries endowed with natural habitats for NHP, such as Japan, India, or Southeast Asian countries, which suffer from increasing conflict between humans and feral monkeys over the last several decades (Dittus, 2012). NHPs become pests because they pilfer food and water near human habitation. ...
Full-text available
We propose novel strategies for primate experimentation that are ethically valuable and pragmatically useful for cognitive neuroscience and neuropsychiatric research. Specifically, we propose Natural Laboratory Complex or Natural Labs, which are a combination of indoor-outdoor structures for studying free moving and socially housed primates in natural or naturalistic environment. We contend that Natural Labs are pivotal to improve primate welfare, and at the same time to implement longitudinal and socio-ecological studies of primate brain and behavior. Currently emerging advanced technologies and social systems (including recent COVID-19 induced “remote” infrastructures) can speed-up cognitive neuroscience approaches in freely behaving animals. Experimental approaches in natural(istic) settings are not in competition with conventional approaches of laboratory investigations, and could establish several benefits at the ethical, experimental, and economic levels.
... Longevity in this population of macaques can exceed 30 years of age, mean lifespan, however, is less than 8 years owed to high mortality among infants and juveniles, and males and females differ markedly in survivorship schedules (Dittus, 2004). Compared to captive or food provisioned populations of other species of macaques, the wild toque macaques show slower population growth and generally greater mortality owed primarily to the effects of a limited food supply in the wild (Dittus, 1980(Dittus, , 2012. ...
Full-text available
The vitamin D receptor is found on most cells, including active immune cells, implying that vitamin D has important biological functions beyond calcium metabolism and bone health. Although captive primates should be given a dietary source of vitamin D, under free-living conditions vitamin D is not a required nutrient, but rather is produced in skin when exposed to UV-B light. The circulating level of 25 hydroxyvitamin D (25-OH-D) considered adequate for humans is a topic of current controversy. Levels of circulating 25-OH-D sufficient for good health for macaques and other Old World anthropoids are assumed to be the same as human values, but data from free-living animals are scant. This study reports values for 25-OH-D and the active vitamin D metabolite, 1,25-dihydroxyvitamin D (1,25[OH]2 D) for wild, forest-ranging toque macaques (Macaca sinica) in Sri Lanka. Plasma samples were obtained from eight adult males, seven juvenile males, six young nulliparous females, nine adult females not pregnant or lactating, eleven lactating adult females, and four pregnant females. Mean values for the complete sample were 61.3???4.0?ng/ml for 25-OH-D and 155.6???8.7?pg/ml for 1,25[OH]2 D. There were no significant differences for either metabolite among age and sex classes, nor between lactating and non-reproductive females. Values from the literature for circulating 25-OH-D in captive macaques are three times higher than those found in this wild population, however, 1,25[OH]2 D values in captive animals were similar to the wild values. The data from this study indicate that anthropoid primates exposed to extensive sunlight will have circulating values of 25-OH-D generally above 30?ng/ml, providing some support for the Endocrine Society recommendations for humans. Current dietary vitamin D supplementation of captive macaques likely exceeds requirement. This may affect metabolism and immune function, with possible consequences for macaque health and biomedical research results.
Many investigators of human-monkey competition (HMC) in Sri Lanka have revealed some common threads. Except at temple and protected sites, all monkeys were considered as household or agricultural pests wherever they shared space with humans. This included the widely distributed toque macaque (Macaca sinica), the grey langur (Semnopithecus priam thersites) of the Dry Zone, and the purple-faced langur (S. vetulus) of the southwestern and central rain forests where human densities and habitat fragmentation were greatest. People sharing space with monkeys resorted to various non-lethal methods to chase monkeys away from their properties and most preferred to have monkeys removed to protected areas; such translocations have been politically popular, though contrary to ecological principles. The main cause of HMC near primate habitats has been environmental conversion to agriculture, whereas in many towns the refuse generated in the wake of widespread growing tourism lured omnivorous macaques towards human habitation and stimulated macaque population growth. While most Sri Lankans share space with monkeys reluctantly, only a minority, flouting cultural restraints, want monkeys destroyed. Nonetheless, a major threat to primate conservation has been habitat loss and the killing of monkeys, especially in the densely populated southwestern area of the island where recent surveys showed that most macaques have been wiped out. Two subspecies, S. v. nestor of the rain forest lowlands and M. s. opisthomelas of the montane forests, are Critically Endangered. Sharing space with monkeys rests on public tolerance, understanding, and empathy with monkeys. Religious concepts venerating monkeys provide fertile ground for this. Our science-based educational documentaries (n > 35), among other efforts, also have contributed to these human sentiments in Sri Lanka and globally. The trends in HMC suggest that protected nature reserves for all wildlife are more secure for primate survival than ethnoprimatology by itself would be. Rudran [Folia Primatologica 2021, DOI: 10.1159/000517176] criticized our recent publication on HMC in Sri Lanka [Dittus et al., Folia Primatologica 2019, 90: 89-108]. We consider his comments as misconstruing efforts in primate conservation through denying the importance of traditional protected areas, overlooking our achievements in educating the public and reducing HMC, as well as misunderstanding the limits of marketing monkeys to tourists as a source of income to support conservation.
Skinfold thickness (SFT) has been used often in non-human primates and humans as a proxy to estimate fatness (% body fat). We intended to validate the relation between SFT (in recently deceased specimens) and the mass of adipose tissue as determined from dissection of fresh carcasses of wild toque macaques (Macaca sinica). In adult male and female toque macaques body composition is normally 2% adipose tissue. Calipers for measuring SFT were suitable for measuring only some subcutaneous deposits of adipose tissue but were not suitable for measuring large fat deposits within the body cavity or minor intermuscular ones. The anatomical distribution of 13 different adipose deposits, in different body regions (subcutaneous, intra-abdominal and intermuscular) and their proportional size differences, were consistent in this species (as in other primates), though varying in total mass among individuals. These consistent allometric relationships were fundamental for estimating fatness of different body regions based on SFT. The best fit statistically significant correlations and regressions with the known masses of dissectible adipose tissue were evident between the SFT means of the seven sites measured, as well as with a single point on the abdomen anterior to the umbilicus. SFT related to total fat mass and intra-abdominal fat mass in curvilinear regressions and to subcutaneous fat mass in a linear relationship. To adjust for differences in body size among individuals, and to circumvent intangible variations in total body mass allocated, for example to the gastro-intestinal contents, dissected fat mass was estimated per unit body size (length of crown-rump)(3) . SFT had greater coefficients of correlation and regressions with this Fat Mass Index (g/dm(3) ) than with Percent Body Fat. Am. J. Primatol. 9999:1-15, 2015. © 2015 Wiley Periodicals, Inc. © 2015 Wiley Periodicals, Inc.
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