Habitat-related variation in movements and fledging success of American black duck broods in northeastern Nova Scotia

Female American black ducks (Anas rubripes) are known to move their broods from low- to high-nutrient rearing sites. We studied the extent of brood movement and fledging success in a northeastern Nova Scotia watershed. Annually, about half the broods moved either overland or along three rivers from small, widely dispersed oligotrophic–mesotrophic wetlands to a large hypertrophic tidal marsh. Mean brood size at fledging was 3.50 in the tidal marsh but 7.05 at the dispersed freshwater wetlands. Females that remained at dispersed sites fledged more ducklings than females that moved to the marsh. Attrition occurred predominantly in the marsh or in transit. Females fledged fewer young when they raised broods at the marsh than when the same females raised broods at inland sites. Females were as successful at nutrient-poor sites as at nutrient-rich sites. The study suggests that concentrating birds in nutrient-rich sites may be counterproductive in terms of female reproductive fitness and population recruitment.