Silent Valley National Park is a protected area in Kerala, India. It is found in the Nilgiri hills and has a main area of 89.52 km (34.56 sq mi). A surrounding area of 148 km (57 sq mi) helps protect the park. The park is home to many rare plants and animals. It was first explored in 1847 by botanist Robert Wight. The park is located near the border of Mannarkkad Taluk in Palakkad district, Nilambur Taluk in Malappuram district, and Nilgiris district in Tamil Nadu, Kerala.

Silent Valley is part of the Nilgiri Biosphere Reserve, an area with high plant and animal diversity. Nearby are the Karimpuzha Wildlife Sanctuary, New Amarambalam Reserved Forest, Nedumkayam Rainforest in Nilambur Taluk, Attappadi Reserved Forest in Mannarkkad Taluk, and Mukurthi National Park in Nilgiris district. Mukurthi peak, the fifth-highest mountain in South India, and Anginda peak are also nearby. The Bhavani River, a branch of the Kaveri River, and the Kunthipuzha River, a branch of the Bharathappuzha River, begin near Silent Valley. The Kadalundi River also starts in the park.

Silent Valley is one of the last untouched areas of South Western Ghats mountain rain forests and tropical moist evergreen forests in India. It connects to the proposed Karimpuzha National Park (225 km (87 sq mi)) to the north and Mukurthi National Park (78.46 km) to the northeast. It is the center of the Nilgiri Biosphere Reserve (1,455.4 km) and part of the Nilgiri Sub-Cluster (6,000 km), a protected area in the Western Ghats World Heritage Site, recognized by UNESCO in 2007.

A plan to build a hydroelectric project in the 1970s threatened the park’s plants and animals. This led to the Save Silent Valley movement, which stopped the project and helped create the park in 1980. The park’s visitor center is located at Sairandhri.

History

The first Western examination of the Silent Valley area’s watersheds happened in 1857 by botanist Robert Wight. The British gave the area its name, Silent Valley, because they believed there were no noisy cicadas there. Another account suggests the name came from changing the local name "Sairandhri" to English. A third story says the name refers to the many lion-tailed macaques, Macaca silenus, living in the area. In 1914, the forest in the Silent Valley area was officially made a reserve forest. From 1927 to 1976, parts of the Silent Valley forest were used for forestry work. In 1928, the spot on the Kunthipuzha River near Sairandhri was chosen as a good place to build an electricity-generating station. In 1958, a study of the area was completed, and the Kerala State Electricity Board proposed a hydroelectric power project that could produce 120 megawatts at a cost of 17 crore rupees.

Environmental concerns

Silent Valley is home to the largest group of lion-tailed macaques, an endangered species of primate. People worried about threats to their habitat led to the creation of Silent Valley National Park.

In 1973, the valley became the center of "Save Silent Valley," India's strongest environmental movement of the decade. The Kerala State Electricity Board planned to build the Silent Valley Hydro-Electric Project (SVHEP), which included a dam across the Kunthipuzha River. The dam would flood 8.3 km of untouched rainforest and harm the lion-tailed macaque. In 1976, the Kerala State Electricity Board announced plans to begin construction, and the issue was brought to public attention. Romulus Whitaker, founder of the Madras Snake Park and the Madras Crocodile Bank, was likely the first person to highlight the small and remote area.

On 7 September 1985, Silent Valley National Park was officially opened, and a memorial to Indira Gandhi was unveiled by Rajiv Gandhi, her son and the next prime minister. On 1 September 1986, the park was named the core area of the Nilgiri Biosphere Reserve. Since then, long-term efforts have been made to protect the Silent Valley ecosystem.

In 2001, a new hydro project was proposed, and the "Man vs. Monkey debate" was revived. The proposed dam (64.5 m high and 275 m long) would be built 3.5 km downstream from the old dam site, 500 m outside the National Park boundary. The Kerala Minister for Electricity called the Pathrakkadavu dam (PHEP) an "eco-friendly alternative" to the old project. The claim was that the PHEP would flood only 0.041 km of land, compared to 8.30 km flooded by the 1970s project. From January to May 2003, a rapid Environmental Impact Assessment (EIA) was conducted. On 15 November, Minister for Forest Binoy Viswam said the proposed buffer zone for Silent Valley would be declared soon.

On 21 February 2007, former Chief Minister A. K. Antony stated that the center had promised to approve the Pooyamkutty project after the Silent Valley proposal was dropped, but this promise had not been kept. The Kerala government had not decided to restart the Silent Valley Hydel Project.

On 18 April 2007, Kerala Chief Minister V S Achuthanandan and his cabinet approved the Pathrakkadavu Hydro-electric project and sent it to the Union Government for environmental approval.

Forests around the national park have been managed to meet revenue goals, such as harvesting bamboo and reed, which affect the park’s long-term protection. Illegal activities, such as growing ganja (Cannabis sativa), have damaged the habitat.

On 21 November 2009, Union Minister of Forest and Environment Jairam Ramesh and Kerala Forest Minister Binoy Viswam announced that the buffer zone of the Park would be added to the park to improve protection.

On 6 June 2007, the Kerala cabinet approved the buffer zone proposal. The new 147.22 km zone would include 80.75 km from Attapady Forest Range, 27.09 km from Mannarkkad Forest Range, and 39.38 km from Kalikavu Forest Range, forming a new range called Bhavani Forest Range. Part of the zone would be added to the existing Silent Valley Range. The cabinet also approved 35 staff to protect the area and two new forest stations in Bhavani range at Anavai and Thudukki. Forest Minister Benoy Viswom said the zone would have reserve forest status and would not affect tribal people in the area. The decision showed the LDF Government’s commitment to environmental protection.

The proposal was sent to Kerala Minister for Electricity, A. K. Balan, who supported the Pathrakadavu hydroelectric project in the

Geography

Silent Valley is shaped like a rectangle, measuring twelve kilometers from north to south and seven kilometers from east to west. It is located between 11°03' to 11°13' N (latitude) and 76°21' to 76°35' E (longitude). The valley is separated from the high altitude plateaus of the Nilgiris Mountains by tall, continuous ridges, including Sispara Peak (2,206 meters) at the northern end of the park. The land slopes gradually downward to the south toward the Palakkad plains, and to the west, it is bordered by uneven ridges. The altitude ranges from 658 meters to 2,328 meters at Anginda Peak, but most of the park lies between 880 meters and 1,200 meters. In evergreen forests, the soil is blackish and slightly acidic, with a lot of organic matter. The rock beneath the soil is granite, along with schists and gneiss, which create loamy laterite soils on slopes.

The Kunthipuzha River flows through the entire 15-kilometer length of the park from north to south into the Bharathapuzha River. This river divides the park into two parts: a narrow eastern section that is 2 kilometers wide and a wider western section that is 5 kilometers wide. The river has clear water and flows all year. Its main tributaries—Kunthancholapuzha, Karingathodu, Madrimaranthodu, Valiaparathodu, and Kummaathanthodu—begin on the upper slopes of the eastern side of the valley. The river is shallow and does not have floodplains or bends. The riverbed drops from 1,861 meters to 900 meters over 12 kilometers, with the last 8 kilometers dropping only 60 meters. Kunthipuzha is one of the less powerful rivers in the Western Ghats, and its area is free from pesticides.

Silent Valley receives a lot of rainfall during the monsoon season, but the amount varies across the region because of the different land shapes. Generally, rainfall is higher at higher elevations and decreases from west to east due to the rain shadow effect. About 80% of the rainfall happens during the southwest monsoon from June to September. The park also gets significant rainfall during the northeast monsoon from October to November.

Because the park is surrounded by hills, it has its own unique climate and may receive some rainfall from clouds forming over the area, in addition to rain from the two monsoons. During the rest of the year, moisture from mist on plants is estimated to provide about 15% of the total water in the rainforest.

In 2006, the Walakkad area of the park received the highest recorded annual rainfall of 9,569.6 mm. Other yearly rainfall amounts include 7,788 mm in 2000; 8,351.9 mm in 2001; 8,465.3 mm in 2004; and 9,347.8 mm in 2005. In the valley (at Sairandhri?), rainfall was 7,788.8 mm in 2000; 8,361.9 mm in 2001; 4,262.5 mm in 2002; 3,499.65 mm in 2003; 6,521.27 mm in 2004; 6,919.38 mm in 2005; 6,845.05 mm in 2006; 6,009.35 mm in 2007; and 4,386.5 mm in 2008. By October 2009, rainfall was 5,477.4 mm. The average annual rainfall in the park from 2000 to 2008 was 6,066 mm.

The average yearly temperature in the park is 20.2 °C. The hottest months are April and May, with an average temperature of 23 °C, and the coolest months are January and February, with an average temperature of 18 °C. Because of the high rainfall, the air is very humid, with relative humidity above 95% from June to December.

Indigenous people

There is no record of people living in the valley in the past. However, the Mudugar and Irula tribal people are native to the area and currently live in the nearby valley called Attappady Reserved Forest. The Kurumbar people live in the highest mountain range outside the park, near the Nilgiris.

Many Mudugar, Irula, and Kurumbar people now work as day laborers and porters. Out of 21 tribal communities in the Attappady range, 16 grow marijuana. Many Mudugar people live in extreme poverty and are often recruited by gangs involved in marijuana. In 2006, a plan was made to hire 50 more men from the 21 tribal communities to work as forest guards.

Flora and fauna

The valley areas of the park are part of the Tropical and subtropical moist forests region. Hilly areas above 1,000 meters are in the South Western Ghats montane rain forests region. Above 1,500 meters, evergreen forests are replaced by shorter forests called sholas, which are mixed with open grasslands. These areas are important for ecologists because they have rich biodiversity that has never been disturbed by human activity. Many threatened species live here, and new plant and animal species are often found in these areas.

BirdLife International lists 16 bird species in Silent Valley as threatened or restricted. These include the Nilgiri wood-pigeon, Malabar parakeet, Malabar grey hornbill, white-bellied treepie, grey-headed bulbul, broad-tailed grassbird, rufous babbler, Wynaad laughingthrush, Nilgiri laughing thrush, Nilgiri blue robin, black-and-rufous flycatcher, Nilgiri flycatcher, white-bellied blue-flycatcher, crimson-backed sunbird, and Nilgiri pipit.

Rare bird species found here include the Ceylon frogmouth and great Indian hornbill. A 2006 survey found the long-legged buzzard, a new raptor species, at Sispara, the park’s highest peak. The survey also found 10 endangered species listed in the IUCN Red List, including the red-winged crested cuckoo, Malabar pied hornbill, and pale harrier. The area is home to 15 bird species that live nowhere else, such as the black-and-orange flycatcher. The survey recorded 138 bird species, including 17 that were newly observed in Silent Valley. The most common bird was the Square-tailed bulbul.

At least 34 mammal species live in Silent Valley, including the threatened lion-tailed macaque, Nilgiri langur, Malabar giant squirrel, Nilgiri tahr, Peshwa’s bat (Myotis peshwa), and hairy-winged bat. There are nine species of bats, rats, and mice.

A study from 1993 to 1996 examined the distribution and numbers of diurnal primates in Silent Valley and nearby areas. Researchers observed 14 troops of lion-tailed macaques, 85 troops of Nilgiri langurs, 15 troops of bonnet macaques, and 7 troops of Hanuman langurs. Nilgiri langurs were spread out, while lion-tailed macaques were found only in the southern part of the park. Bonnet macaques and Hanuman langurs were seen less often. Silent Valley remains one of the few undisturbed habitats for the endangered lion-tailed macaque and Nilgiri langur.

At least 730 insect species have been identified in the park. The most common groups are Lepidoptera (butterflies and moths) and Coleoptera (beetles). Many species have not yet been classified, and more research is needed.

Scientists have recorded 33 species of crickets and grasshoppers, including one new species. They also found 41 species of true bugs, eight of which are new. There are 128 beetle species, 10 of which are new.

Over 128 butterfly species and 400 moth species live in the area. A 1993 study found butterflies from nine families, with the most species in the Nymphalidae and Papilionidae families. Thirteen butterfly species are found only in South India, and five of these are protected. Seven butterfly species were seen migrating in large groups toward Silent Valley. In one case, birds tried to catch these butterflies.

In 2018, a study by the Indian Dragonfly Society and the Forest and Wildlife Department found 83 dragonfly and damselfly species in the park’s buffer zone. These included species like Indosticta deccanensis and Burmagomphus laidlawi. In 2019, another study found 75 species, including eight new ones, bringing the total to 91. A 2023 study added three more species, totaling 103. A 2025 study added six more, bringing the total to 109.

At least 500 species of earthworms and leeches have been identified in the park.

The Silent Valley Bush Frog, Raorchestes silentvalley, was first described in 2016 and named after the park.

The valley has about 1,000 flowering plant species, 108 orchid species, 100 ferns and fern allies, 200 liverworts, 75 lichens, and about 200 algae. Many of these plants are found only in the Western Ghats.

Scientists have identified 966 angiosperm species (flowering plants) in the park, grouped into 134 families and 599 genera. There are 701 dicotyledons (a type of plant) in 113 families and 420 genera, and 265 monocotyledons in 21 families and 139 genera. Orchids are the most common group, with 108 species, including rare and endangered ones like Ipsea malabarica and Eria tiagii. Other common groups include grasses (56 species), legumes (55 species), Rubiaceae (49 species), and Asters (45 species). Many plants are rare, endemic, or valuable, such as cardamom, black pepper, yams, beans, pest-resistant rice, and 110 Ayurvedic medicine plants. Seven new plant species have been found, including Impati

Genetic resources

Throughout human history, about 10% of the genetic material found in wild plants has been used to create crops that are more flavorful and produce more food, such as cereals, fruits, and vegetables. To ensure enough food for the future, it is important to protect the remaining 90% of wild genetic material by preserving areas with high biodiversity, like Silent Valley.

The National Bureau of Plant Genetic Resources of ICAR (India), Plant Exploration and Collection Division, has identified Silent Valley as a region with high biodiversity and a valuable source of genetic material for improving plants through scientific methods. One example of using wild plant genetic material is selecting genes from wild rice species, Oryza nivara (found in central India) and Oryza pittambi (found in Silent Valley), to help create disease-resistant hybrid rice varieties, such as IR-36. These varieties played a major role in the Green Revolution across Asia.

Additionally, studies of bacteria found in the soil of Silent Valley, known as plant growth-promoting rhizobacteria, showed that a specific strain, IISR 331, can increase the growth of black pepper cuttings by 228%. In laboratory tests, this strain also reduced the spread of a common plant disease called Phytopthora capsici by 82.7%.

Challenges

Fire is a serious danger to forests in Kerala. People who raise animals sometimes burn areas to grow fresh grass for their livestock, especially during dry seasons when fires are more likely. Illegal activities, such as growing cannabis, hunting, cutting trees, collecting forest products that are not wood, and carelessness by tourists or pilgrims, also cause large forest fires.

Silent Valley is known for having some of India’s largest illegal cannabis plantations. Cannabis has been traditionally grown in these forests, and some people rely on growing cannabis for their income. Tribes like the Irula, Muduga, and Kurumba (especially the Kurumba) have a history of cultivating cannabis. A seedless type of cannabis grown in Silent Valley is called Sairandhri and is famous worldwide for its quality.

According to a former official, Madhava Menon, the cannabis grown in this area is among the best in the world and is sold globally. Illegal cannabis growers have destroyed hundreds of acres of tropical forest in the Attappady Hills, including areas near Silent Valley, to plant cannabis. The Forest Department planned to stop illegal cannabis farming in the Attappady forests by April 2006.

In December 2014, Maoist groups attacked the ticket counter of Silent Valley National Park at Mukkali. Since then, a large group of special police has been stationed there. However, the growing presence of Maoist groups in eastern Kerala’s tribal areas remains a serious problem.