Annual wetland bird monitoring in the Tamiraparani Basin,
The plains of Tirunelveli and Thoothukudi districts of Tamil Nadu state receives about 800 mm of annual rainfall as they fall in the rain-shadow region of the Agasthyamalai, part of a global biodiversity hotspot. The Tamiraparani, along with its tributaries originating from Agasthyamalai, flows through these districts and is one of the perennial rivers in south India. It connects a network of several hundreds of tanks facilitating irrigation of thousands of hectares of fields cultivated largely with paddy, banana and sugarcane. The Tamiraparani River is the lifeline of the region that otherwise could have been parched semi-arid landscape. These tanks in south India are of ancient origin, dating back to 4th and 5th century A.D. They were constructed by chieftains and local landlords and maintained by the local communities. Today Tirunelveli district boasts of 2500 wetlands, of which 1222 are managed by the Public Works Department, fed by irrigation channels. Other tanks, which are vested with the panchayats, are all rain-fed.
These tanks and canal system provide water even during the summer and support diverse plant and animal communities, which are unique to Tamiraparani river basin. Our recent study of wetland plant communities in this network of tanks showed that 40% of the 93 species were sparsely distributed. Also, we have recorded stupendous bird diversity in these tanks that serve as over-wintering grounds for as many as 15 migratory bird species coming from Central Asia and Europe.
We initiated a community wide citizen-based water bird count in the irrigation tanks in 2011. This Tamiraparani water bird count has since picked up and we are in the 13th year wherein over 100 volunteers across eleven years and 122 irrigation tanks in the Tamiraparani river basin were sampled. The analysis indicates species stability though total abundance has declined. Fourteen out of the 65 species showed a declining trend, of which 11 were residents and three were winter migrants. Large reservoirs in the river basin serve as a refuge for water birds during periods of severe drought. Currently a cluster of eight tanks in winter and seven in summer were prioritised in the landscape for conservation action.