We carry out a long-term study on the birds of the river Kaveri and river Kollidam in Tamil Nadu, with particular focus on threatened riverine birds such as the Black-belied Tern Sterna acuticauda, River Tern Sterna aurantia and Lesser Fish-Eagle Icthyophaga humilis. 

The Kaveri river originates from Talakaveri in the Brahmagiri range in the Western Ghats, Kodagu district of the state of Karnataka. It enters Tamil Nadu through Cauvery Wildlife Sanctuary near Hogenakkal, and it empties into the Bay of Bengal near Poompuhar. The entire length of the Kaveri river from its origin in the Western Ghats is about 780 km, of which nearly 450 km is in Tamil Nadu. Most of the river flows through human-dominated landscapes, while for about 60 km of the river flows through the Cauvery Wildlife Sanctuary. The major habitat along the sanctuary is riparian forest and dry deciduous forest. This river is also an important habitat for various other taxa such as the vulnerable smooth-coated otter and several freshwater terrapins.

We conducted a bird survey (point counts) in the Kaveri and Kollidam rivers in Tamil Nadu. Of the total c.450 kms stretches of the Kaveri and Kollidam rivers within Tamil Nadu, we surveyed c. 300 kms. In total, we have surveyed 527-point locations (every 500 m). From this effort, we recorded Black-bellied Terns only in 12 points (only in Kollidam river). All these locations fell within about 60-70 km of the entire river stretch surveyed. Apart from this, we conducted a survey in the Cauveri North Wildlife Sanctuary (along a c.70 km stretch of the Kaveri river) from Mekedatu to Hogenakkal to the backwaters of the Mettur reservoir. We recorded River Terns and Lesser Fish-eagles, but did not record Black-bellied Terns there. We have also been conducting regular monitoring of Black-bellied Terns in the only stretches where this endangered bird has been recorded during our survey, essentially to know the population, habitat requirements, breeding locations and threats.