Brood survival and recruitment of Mallards in relation to wetland density and hatching date

Abstract

Reproductive success in birds often is measured in terms of the proportion of nests that hatch or fledge young. We assessed survival of 35 Mallard (Anas platyrhynchos) broods near Yorkton in east-central Saskatchewan, Canada, from 1990 to 1993. Brood survival was higher for offspring that hatched early in the breeding season in three of four years when wetland abundance declined over the summer. Seasonal patterns of wetland abundance were reversed in 1993, and early hatching broods suffered higher mortality. A more accurate measure of reproductive success is the number of young that survive to breed, i.e. recruitment. Ducklings were tagged at Yorkton and on the St. Denis National Wildlife Area (1985 to 1995), enabling us to identify individuals that returned to breed in subsequent years. Female recruits were more likely to originate from early hatched nests at both sites. With respect to recruitment, we also tested for an additional advantage of hatching early, over and above that associated with duckling survival. There was no statistical difference in the seasonal distribution of nests producing recruits compared with broods that successfully fledged at least one young. Thus, the selective advantage to nesting early for Mallards likely is driven by a seasonal decline in duckling survival, which in turn may be associated with decreasing wetland density.