Thattekkadu is made up of tropical evergreen and deciduous forests and some grassland patches. This globally acclaimed bird sanctuary owes much of its fame to Dr. Salim Ali, the internationally renowned ornithologist. After his famous bird survey of Travancore in the early 1930s, he reported that this area is extremely rich in bird diversity and that it should be made into a bird sanctuary. Thus his efforts were instrumental in the formation of this sanctuary to a large extent. More than 300 species of birds are found here.
Spread across 25 sq. km. the sanctuary lies between the tributaries of the River Periyar like a peninsula. Birds like Srilankan Frogmouth, Racket tailed Drongo, Bronzed Drongo, Whitebellied Treepie, Shama, Yellow-browed Bulbul, Rufous Babbler, Malabar Parakeet, Whitebellied Blue Flycatcher, Malabar Grey Hornbill, are some of the birds that can be easily seen here.
Thattekkad also has extensive plantations of teak, rosewood, mahogany. The dense forest is also home to nearly 28 species of mammals and about 9 species of reptiles.