BIOLOGY OF THE TRISTAN THRUSH NESOCICHLA-EREMITA

The Tristan Thrush Nesocichla eremita is a little known species restri cted to the Tristan da Cunha Islands, South Atlantic Ocean. We describ e several aspects of the species' biology, based primarily on observat ions made at Inaccessible Island. Tristan Thrushes are monomorphic, as suming adult plumage after a partial juvenile moult. There is little s ex-related size dimorphism within island populations, which may reflec t 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 raise d from clutches of two eggs at Inaccessible and Tristan. Three-egg clu tches have only been recorded at Nightingale Island, where they compri se about half of all clutches. Adults perform a very soft, melodic war bling song, which is most frequently uttered immediately prior to the spring breeding season. Typical calls are simple, high-pitched whistle s. Adults moult after the breeding season, and primary moult is comple ted within 80 days. Moult commences at least one week earlier at the c oast 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.