The contributions of body tissues, respiratory system, and plumage to buoyancy in waterfowl

Abstract

This study examines buoyancy partitioning between body compartments in diving and surface-feeding Anatidae. Body tissue and plumage densities and the volumes of air in the respiratory system and plumage were analyzed using cadavers and restrained live specimens of waterfowl. The densities of the skeleton and remiges of surface feeders were significantly lower than those of divers but the differences were not sufficient to significantly reduce the body tissue density and buoyant force of divers. There were no other statistically significant differences in the body tissue densities of diving and surface-feeding waterfowl. The densities of contour feathers, down, and remiges were markedly different from each other but the net buoyant force of the feathers was less than 5% of that caused by the air trapped in the plumage layer. All cadavers were negatively buoyant in the absence of air in the respiratory system and plumage. Despite similar net buoyant forces, there were large differences in the volumes of air in the respiratory system and plumage between restrained ducks and cadavers. These results indicate that the use of cadavers or restrained ducks to determine net buoyancy, and hence power output, during voluntary foraging behaviour is unreliable.