Breeding success of boreal mallard and wigeon in relation to population density and food resources

Breeding success of mallard and wigeon was studied for 12 years in a boreal lake area in southern Finland. Aquatic and surface-emerging prey were trapped to obtain annual indices of food abundance. The average density of mallards was 0.42 pairs per 1000 m shore line and that of wigeon 0.18. The mean brood production per pair was 0.24 in mallard and 0.41 in wigeon. We correlated brood:pair and duckling:pair ratios to pair density and per capita food availability to test whether per capita breeding success decreases in a density-dependent way when pair density or the number of nesting pairs per available food unit increases. No density-dependent pattern was found in mallards. In wigeon, in contrast, we found two independent patterns of density dependence. Per capita brood production correlated negatively with pair density, and brood:pair and especially duckling:pair ratio correlated negatively with per capita abundance of surfaceemerging prey.