Summary M.W. Fraser, P.G. Ryan, W.R.J. Dean, D.J. Briggs, & C.L. Moloney 1994. The biology of the Tristan Thrush Nesocichla eremita. Ostrich 65:14-25. The Tristan Thrush Nesocichla eremita is a little known species restricted to the Tristan da Cunha Islands, South Atlantic Ocean. We describe several aspects of the species' biology, based primarily on observations made at Inaccessible Island. Tristan Thrushes are monomorphic, assuming adult plumage after a partial juvenile moult. There is little sex-related size dimorphism within island populations, which may reflect limited genetic variation. Tristan Thrushes are generalist foragers, using a variety of techniques to consume both animal and plant matter. Breeding occurs during the austral spring, with a single brood raised from clutches of two eggs at Inaccessible and Tristan. Three-egg clutches have only been recorded at Nightingale Island, where they comprise about half of all clutches. Adults perform a very soft, melodic warbling song, which is most frequently uttered immediately prior to the spring breeding season. Typical calls are simple, high-pitched whistles. Adults moult after the breeding season, and primary moult is completed within 80 das. Moult commences at least one week earlier at tie coast than on the plateau (elevation 250–500 m) at Inaccessible Island. We provide a revised population estimate for Inaccessible Island, and make recommendations for the species' conservation.