The Pichavaram mangroves and its associated wetlands are facing an alarming decline in bird population.
According to a study, Pichavaram — the second largest mangrove wetland eco-system in the country and an important area for migratory birds — has lost 40 per cent of waterbird species in the past three decades.
Located about 190 km south of Chennai, the count of migratory birds is plummeting in the mangrove wetlands, mainly because of habitat loss due to human disturbance, cattle grazing, over-fishing and reckless tourism.
The 1994 cyclone and 2004 tsunami hit the coast and structurally damaged to the mangroves. As a result, several bird species were lost from the eco-system, says the study by AVC College, Mayiladuthurai.
The three-year study recorded only 49 species of waterbirds, out of 82, which was recorded in an earlier study during 1984-1988. Lesser flamingos and Asian dowitcher no longer seem to appear in the area. Little green heron, Painted stork, Black headed Ibis, Oriental darter are four species out of 49 that were designated as near threatened.
The coastal wetlands are situated at the mouth of the Vellar, Coleroon and Uppanar rivers in Cuddalore district. About 50 per cent of the area is covered by mangroves, 40 per cent wetlands and rest comprises mudflats, which offers roosting and foraging grounds for the birds.
“Obviously declining of birds is an indicator that Pichavaram mangrove is facing some threat,” says S. Sandilyan, one of the authors, who now works for the National Biodiversity Authority in Taramani.
“Excrement [guano] of waterbirds is a good source of nutrients. It is rich in nitrogen and phosphorus and plays a vital role in the development of a healthy mangrove system. If the birds decline, the food chain gets disturbed affecting the health of coastal mangroves,” he says.
The study, co-authored by K. Thiyagesan and R. Nagarajan, was recently presented at a consultative workshop on restoring wetlands of Tamil Nadu.
In another study, Sandilyan and Kathiresan have found out that plastics pose a serious threat to Pichavaram mangroves and its associated wetlands. Tourists’ reckless attitude has been increasing over the years. Plastic carry bags clog aerial roots of mangroves, leading to death of young plants.
Hanging over the tree branches, the carry bags produce a peculiar sound during wind flow causing panic among foraging migratory and resident waterbirds. The floating water bottles may frighten the birds and alter its behaviour as well as of other keystone species of mangroves such as crabs, Sandilyan says.
