Burger A.E. (1981) Food and foraging behaviour of Lesser Sheathbills at Marion Island. ARDEA 69 (2): 167-180

Lesser Sheathbills Chionis minor were the only birds at Marion Island, in the Sub-Antarctic, entirely restricted to land-based food. At penguin colonies the sheathbills fed on carcasses, eggs, small chicks, excreta and seafood kleptoparasitised from the penguins. At seal colonies they commonly ate carcasses, placentas and blood. In the intertidal zone the sheathbills took algae (Porphyra sp.), amphipods, limpets and other invertebrates, and from kelp jetsam on beaches they took kelp flies and oligochaetes. On the vegetated coastal plain they ate invertebrates, mainly earthworms and insects. Seasonal changes in the foraging habits were dictated by the availability of food from penguins, which provided concentrations of food with high energy, protein and fat contents. Predatory skuas Catharacta skua lonnbergi affected the foraging of Lesser Sheathbills on the coastal plain. The foraging habits of adult, subadult and juvenile Lesser Sheathbills were broadly similar but adults fed more commonly in penguin colonies. Three factors which favoured a broad trophic niche in Lesser Sheathbills were: seasonal fluctuations in availability of preferred food from penguin colonies; the paucity of interspecific competition; and short-term weather variations, particularly snow and heavy waves. Co-existence between Lesser Sheathbills and the other four species of predator-scavenger birds at Marion Island was probably facilitated by differences in specific body masses. Lesser Sheathbills foraged in territories, in flocks and solitarily; each social arrangement appeared to be adapted to the nature of the food resource being exploited. The close association with penguins is fundamental to the success of sheathbills as land-based birds on inhospitable islands.