Sri Lanka is transitioning to a scientific and humane approach to managing its persistent human-monkey conflict, with the first field applications of a monkey sterilisation programme set to begin.
According to Prof. Ashoka Dangolla, the lead investigator of a special commission appointed by the President to look into the issue, the initiative will involve using contraceptive loops and vasectomies to control the monkey population.
For years, rural communities and farmers have faced immense challenges due to crop and property damage, incurring losses of millions of rupees annually. Simultaneously, conservationists have warned against culling the toque macaque, an endangered species endemic to the country.
This sterilisation programme is a compromise aimed at protecting both human livelihoods and the ecological balance. Field surgeries are expected to commence as early as September. The project is a consequence of the national census on wildlife that damages agricultural crops, which was conducted earlier this year.
Census findings
The census conducted on 15 March targeted four key species identified as the most destructive: macaques, langur monkeys, giant squirrels, and peacocks. The data collection effort was executed by grama niladharis, Samurdhi development officers, and agricultural officers across the island, working under the guidance of district and divisional secretaries.
The initial census figures revealed staggering populations: over 5.1 million langurs, 4.2 million peacocks, 2.6 million giant squirrels, and 1.7 million macaques. However, a verification process found public-reported data on langurs and macaques to be only 50% accurate. Consequently, the committee has halved the counts for these two species to establish working figures for policy planning.
The data pinpointed specific geographic impacts. Kandy, Anuradhapura, and Kurunegala were classified as high-risk districts, being severely affected. They are joined by eight heavily affected districts, including Kalutara, Galle, Matara, and Ratnapura. In contrast, Jaffna, Kilinochchi, Batticaloa, and Nuwara Eliya were noted as less affected.
In response, the committee has proposed a comprehensive set of measures. The strategies range from immediate practical steps to long-term legal reforms. Key recommendations include implementing proper waste management to eliminate urban food sources for wildlife and deploying the Civil Security Force to high-damage areas to chase animals away with firearms.
For sustainable management, the report advised the Department of Wildlife Conservation to consider lowering the protected status of giant squirrels and peacocks to allow for population control. Other forward-looking proposals included investing in research for electronic deterrents, implementing animal sterilisation programmes, erecting electric fences around large farms, and establishing a robust new legal framework for wildlife management.
Origins of a humane solution
The sterilisation initiative owes its origins to the direct plea of Ellawala Group of Companies Director Chanaka Ellawala. The Ellawala plantation in Kalawewa, renowned for cultivating the highly sought-after TJC mango variety, had been suffering severe damage due to marauding monkeys. Rather than pursue poisoning or culling, Ellawala appealed to scientists to find a sustainable, non-lethal solution.
Responding to this request, Prof. Dangolla and his team sought financial backing from the Sri Lanka Council for Agricultural Research Policy (SLCARP). With SLCARP’s support, a multi-disciplinary research programme was launched, bringing together medical professionals, zoologists, veterinarians, and agricultural experts.
Among them were Prof. Nawaz Jiffry, a gynaecologist who contributed his expertise in reproductive health; Prof. Kithsiri Ranawana, a zoologist with extensive experience in primate ecology; veterinarians Dr. Sashikala Gamage, Dr. Roshan Kahatapitiya, and Dr. Charith Abeyratne; Dr. Pramuditha Devasurendra and Dr. Akalanka Pinideniya of the Department of Wildlife Conservation; and Dr. Loshan Moonesinghe from the Ministry of Health’s Family Health Bureau.
Clinical research and early challenges
The project began with laboratory-based research, examining the possibility of adapting existing human contraceptive technologies for monkeys. Working closely with Dr. Moonesinghe, the team resized copper T-loops used in human family planning to suit the smaller uterine anatomy of female monkeys. To test feasibility, the reproductive tracts of monkeys that had died from natural or accidental causes were studied, and then the first live trials began.
Ten monkeys from the Ellawala plantation underwent the surgical insertion of these modified loops. With the aid of ultrasound and X-ray imaging, researchers were able to monitor whether the devices remained in place. The findings, however, revealed significant hurdles.
Expulsion rates were high (estimated at around 40%) because monkeys exhibited stronger uterine contractions and higher levels of secretions compared to humans. Additionally, the oestrous cycle of female monkeys remained poorly documented, making it difficult to determine the optimal timing for insertion.
Yet, the trials also revealed a crucial breakthrough: if the loop remained inside the uterus for at least three months, it typically became permanent, ensuring life-long infertility. Encouraged by this outcome, the team began exploring ways to make the devices more resilient.
An unexpected innovation came when Prof. Dangolla met Dr. Viraj Sanjeeva, a local inventor, who collaborated with the researchers to design a 3D-printed intrauterine device tailored specifically for monkeys. This custom device is expected to be tested within the year and could overcome many of the limitations identified in the earlier trials.
Transitioning from laboratory to field
With proof of concept established, the project is now transitioning into field applications. A specialised surgical unit has been built on the Ellawala plantation, where the first mass sterilisation surgeries will be carried out in September. The programme will adopt a dual approach: intrauterine loops for females and vasectomies for sub-adult males.
Prof. Dangolla emphasised that success would be measured not only in terms of medical outcomes but also in ecological stability. “We must ensure that sterilisation does not destabilise the troop structures of monkeys,” he said. “If we intervene carelessly, we could create aggressive behaviours or territorial imbalances that worsen the conflict. Population control must remain ethical as well as scientific.”
Presidential commission and policy support
The sterilisation programme gained official recognition when a special commission on the human-monkey conflict was appointed by the President, with Prof. Dangolla serving as the principal investigator.
According to him, the commission is composed of high-level officials, including the Directors General of the Wildlife, Forest, and Land Use Departments, as well as representatives from the Army, Navy, Air Force, and relevant ministries like Irrigation and Mahaweli. Prof. Dangolla and Prof. Sampath Seneviratne from the University of Colombo are the only academics on the commission.
Prof. Dangolla said that the commission was focusing on monkeys that were troublesome to people and lived in close proximity to human settlements, not those in the wild. A key step has been to work with the data from a public monkey count, despite some criticism of its methodology.
While the count provides a baseline, the committee has identified Kandy as a priority district due to its high monkey population density. As a result, Prof. Dangolla and Prof. Seneviratne, with the assistance of the University of Peradeniya’s Zoology Department, have finalised a project to conduct a more thorough and scientific monkey count in the Kandy District. They have secured an initial budget of Rs. 5 million out of a total of Rs. 26 million allocated for this project, with funding and a vehicle provided by the Presidential Secretariat.
Management, not eradication
Alongside the commission, the inter-ministerial committee for minimising wildlife damage to food crops, of which University of Peradeniya Department of Crop Science Prof. Buddhi Marambe is a member, has also taken a close interest in the project.
Prof. Marambe described sterilisation as “the most practical and humane method currently available,” but he cautioned that it must be applied selectively.
“The toque macaque is endemic to Sri Lanka. If we sterilise every female, we run the risk of eliminating the species altogether,” he said. “The objective is not eradication but management. Selective sterilisation, applied in hotspot areas where the conflict is most severe, will give us balance.”
Prof. Marambe also highlighted the limited value of male sterilisation alone. “A troop’s dominant male can be sterilised, but another will simply take his place. That’s why vasectomies must be combined with targeted sterilisation of females to have meaningful impact,” he said.
In addition to the census, Prof. Dangolla has proposed a two-pronged approach for the Hewaheta electorate, recognising that science alone cannot resolve the problem. The first part involves educating the public in 15 different locations to help them understand that monkeys are not their enemies. The goal is to discourage inhumane practices such as poisoning and shooting.
The second part involves population control. Prof. Dangolla’s team plans to capture monkeys, perform vasectomies on males, and insert contraceptive loops in suitable females. The sterilised monkeys will then be released onto a small island within the Randenigala Reservoir.
While acknowledging that translocation was not a permanent solution, this step aims to demonstrate that humane population control is possible. “These forested islands could serve not just as habitats but also as eco-tourism attractions. If local communities see economic benefit in protecting sterilised troops, they will become stakeholders in conservation rather than adversaries,” Prof. Dangolla said.
Another critical component of the programme is disease monitoring. With support from the University of Sri Jayewardenepura, the University of Colombo, and the Faculty of Science at the University of Peradeniya, researchers are investigating whether monkeys act as carriers for diseases such as dengue, chikungunya, malaria, and monkeypox.
“Every monkey undergoing sterilisation will also be tested for disease markers. We need to understand whether monkeys are playing a role in transmitting illnesses to humans. The sterilisation programme gives us an unprecedented opportunity to study this connection,” said Prof. Dangolla.
Tracking sterilised monkeys is essential to measuring the programme’s success, according to Prof. Dangolla. “Several identification methods are under review, including tattooing, freeze branding with liquid nitrogen, and microchipping. A key breakthrough came when Errol Dharmaratne donated microchips, enabling the team to experiment with advanced electronic tagging for precise, long-term monitoring,” he said.
“This is pioneering work. No other country has developed a comprehensive system to track sterilised monkeys in the wild. If we succeed, Sri Lanka could provide a model for the entire region,” he added.