When dawn breaks over Silent Valley National Park in Kerala, the forest is anything but mute. From the high canopy comes the resonant whoop of lion-tailed macaques, rare primates found almost nowhere else on earth. Their guttural calls echo through the misty valleys, mingling with the metallic cries of racket-tailed drongos, the steady drumming of woodpeckers, and the musical whistles of thrushes. Streams gurgle down mossy rocks, and the wings of hornbills beat the air like sails.
Yet for all these sounds, there is something missing. In most tropical forests, cicadas scream from the treetops, their piercing calls swelling and falling in waves until the whole forest vibrates with their presence. In Silent Valley, however, that familiar chorus is absent. It is this striking hush—amid all the other noises of life—that gave the forest its English name: Silent Valley.
Cicadas are usually impossible to ignore. Their life cycle is a lesson in patience: nymphs live underground for years, feeding on the sap of roots, before emerging for a brief, noisy adulthood. Their calls—produced by vibrating membranes on their abdomens—can reach over 100 decibels, loud enough to drown conversation. For ecologists, cicadas are not just sound makers but important players in the food web, nourishing birds, reptiles, and mammals while aerating soil and cycling nutrients back into the ecosystem. In most rainforests, they are the beating pulse you cannot escape. But in this 90-square-kilometre stretch of Kerala’s Western Ghats, their chorus is absent.
The British botanist Robert Wight noted the unusual silence here as early as the 1840s. Later, Indian naturalists confirmed the observation. Cicadas were found in Kerala and in patches of adjoining forests, but not in the deep interior of Silent Valley. Over the years, the question grew into an ecological riddle: why would a rainforest so rich in biodiversity, harbouring rare primates like the lion-tailed macaque and over a thousand species of flowering plants, lack something as common as cicadas?
Theories behind the silence
Scientists have put forward several explanations. Some point to the valley’s unique topography. Silent Valley is a bowl-shaped depression surrounded by steep ridges, perpetually shrouded in mist and drenched by heavy monsoon rain. Its soils remain moist and shaded for most of the year, possibly unfavourable for cicada nymphs that require drier, sunlit conditions for their underground development. Others suggest that the particular composition of tree species here creates leaf litter and soil dynamics unsuitable for cicada life cycles.
Another hypothesis is that cicadas were once present but disappeared due to subtle climatic shifts over centuries. Or perhaps, as some entomologists argue, they were never abundant here to begin with, and what appears as “absence” is in fact a natural baseline for this forest.
While scientists puzzled over the missing insects, local communities had a different relationship with the forest. For the Kurumbas and Mudugas, tribal people who lived along the fringes, the valley was never silent. They grew up surrounded by the calls of birds, the murmur of streams, the croaks of frogs. The absence of cicadas was not a mystery—it was simply part of their forest’s identity.
The “silence” took on symbolic meaning only during the 1970s and 1980s, when the proposed Silent Valley hydroelectric project triggered one of India’s fiercest conservation battles. Environmentalists and writers seized upon the name, using it as a metaphor. If the valley was silenced by the absence of cicadas, they argued, it must not be drowned further by the noise of turbines and the death of its wildlife. The lion-tailed macaque became the mascot of the movement, but the “silent” forest became its soul. The campaign eventually led to the cancellation of the dam and the declaration of Silent Valley as a national park in 1984, a landmark victory for India’s environmental movement.
For visitors, the missing cicadas create a heightened sensory experience. Instead of being overwhelmed by insect noise, trekkers describe hearing each drop of water, each flutter of wings. The silence makes the forest feel more intimate, amplifying every detail. It also makes the place uncanny—an ecosystem that feels incomplete, as though something essential is withheld.
Yet absence is never permanent in nature. Ecological systems are dynamic, and even the most stable-seeming patterns can shift. And in Silent Valley, recent field surveys and anecdotal reports suggest something extraordinary: cicadas may be making a cautious return.
“The gradual return of cicadas suggests slow ecological changes and could be signs of resilience in the habitat. Though present in a smaller population it indicates shift in ecosystem dynamics as they play an important role in nutrient cycling and food web. Their presence can be an indicator of microhabitat recovery too. Studies hypothesise that their return may be due to a gradual changes in vegetation structure, climate change or natural dispersal from adjoining landscapes. At the same time, it raises important questions regarding long-term population viability, potential competition with other insect guilds and the impact of anthropogenic pressures on the species distribution. However long-term monitoring of cicada diversity and their abundance in Silent Valley, with the help of surveys is required to understand if this represents a stable recovery or is a transient phenomenon,” said Arya S, research head, Plant Taxonomy Division, Travancore Institute for Bioscience Research (TIBR), Thiruvananthapuram.
According to K Sujana, scientist with the Botanical Survey of India (MoEF&CC), Southern Regional Centre, Coimbatore, the resurgence of cicadas in Silent Valley is a telling sign of ecological upheaval. “Habitat modifications triggered by invasive plants and the shrinking distribution of native tropical species, along with rising temperatures and erratic rainfall, appear to be fuelling this resurgence. It reflects both environmental stress and the inherent resilience of the ecosystem. In many ways, the cicadas’ return underscores how the soundscape of Silent Valley mirrors the unfolding story of climate change and biodiversity shifts across the Western Ghats,” she said.
For scientists working in the region, this isn’t just about insects but about what they reveal of the forest’s health. As Marri, a field researcher who has been tracking biodiversity changes in the Western Ghats, explained: “The return of cicadas is like a whisper from the forest telling us something is changing. Whether that change is positive recovery or a symptom of larger stress, we don’t yet know. But their calls—rare as they are—remind us that ecosystems are alive, fluid, and never frozen in time.”
Silent Valley today is not entirely untouched by human presence. While the core remains protected, surrounding areas face pressures from agriculture, plantations, tourism, and climate change. Shifts in rainfall patterns, warming temperatures, and edge effects could alter the valley’s ecological equilibrium, opening niches for species that were once absent. Cicadas may be beneficiaries of such changes, but so too could invasive species.
Ecologists warn that it is crucial to monitor these shifts carefully. The reappearance of cicadas might be a symbol of recovery—or a warning sign of disruption. What seems like nature “healing” can also mask deeper imbalances. The only way to know is through long-term, systematic monitoring of insect populations and habitat conditions.