Nutrient-reserve dynamics of semiarid-breeding White-faced Whistling Ducks: a north-temperate contrast

Abstract

Little is known about the nutrient-reserve dynamics of waterfowl that breed in semiarid environments. Breeding White-faced Whistling Ducks, Dendrocygna viduata (L., 1766), were collected on the Nyl River floodplain, South Africa, during 1992–1993 and 1995. Mass of major lipid (wet skin + visceral fat + abdominal fat) and protein (breast muscle + leg muscle + gizzard) deposits and organs of males and females were evaluated in relation to sex and reproductive stage. Both sexes arrived at breeding areas with large lipid reserves and did not store additional lipid after arrival. Stored reserves enabled females to begin laying shortly after arrival, an important adaptation to ephemeral wetlands in semiarid environments. Females catabolized at least 37 g of lipid and 27 g of body protein during rapid follicular growth and ovulation. This accounted for 87% of their total lipid and 60% of their protein requirements during egg laying. Males catabolized at least 19 g of lipid between arrival and the end of laying. Although diets of breeding White-faced Whistling Ducks are high in fat, females satisfied most of their lipid requirements for clutch formation from endogenous reserves. Female White-faced Whistling Ducks can reproduce despite their reliance on a relatively low protein diet, and this suggests that they efficiently assimilate amino acids from plant matter. Biparental care apparently decreases the reliance of female White-faced Whistling Ducks on stored nutrients after ovulation, thereby allowing greater allocation of stored nutrients to egg production.