Foraging behaviour and energetics of the Hawaiian Goose Branta sandvicensis

Abstract

The Hawaiian Goose fed on 31 plant species; grasses predominated in most seasons, while berries were favored during incubation. The relative amount of these foods in the diet varied between sexes, bird-class, area and date. Variation in breeding success within and between sub-populations was determined probably by local climate and subsequent plant phenology. We observed a seasonal decline in food quality and density, i.e. a decreasing protein content in grasses, a decline in density of grass seedheads and a decline in water content and density of berries. It is likely that this seasonal pattern restricts the period Hawaiian Geese have available for breeding, just as the spring flush of plant growth delimits the time for reproduction in arctic-breeding geese. At the Volcanoes study site, some of the breeding pairs supplemented their berry diet by flying to grass land some distance from the nest; at Haleakala, all incubating pairs used pastures. We argue that in order to save the goose, managers will have to employ a prolonged, intensive hands-on approach to management, by removing predators and creating and sustaining high-quality grassland habitats well into the future. Refuges should be located near to natural scrubland nesting habitat, as geese in these areas will continue to utilize the full range of foraging skills that characterize the species.