American Black Duck and Mallard Breeding Distribution and Habitat Relationships along a Forest–Agriculture Gradient in Southern Québec

Abstract

Although the American black duck (Anas rubripes) has been designated a priority species in eastern North America, no systematic survey has been done in the agricultural lowlands of southern Quebec, where the species is suspected to be relatively abundant and cohabits with the mallard (Anas platyrhynchos), often considered as a competing species. During the spring of 1998 and 1999, we surveyed breeding waterfowl in 343 4-km2 plots distributed in the lowlands of the St. Lawrence Valley and Lac-Saint-Jean, Canada, and in agricultural areas of Abitibi-Temiscamingue, Canada. American black duck densities were higher in dairy farm and forested landscapes (>39 indicated breeding pairs [IBPs]/100 km2) than in cropland landscapes (8 IBPs/100 km2). Mallard densities were similar across all landscape types (30–43 IBPs/100 km2). Habitat modeling using data derived from satellite imagery indicated that the presence of black ducks decreased with increasing areas of corn, ploughed fields, and deciduous forests, whereas it was favored in areas where topography was undulating with slopes of 10–15%. The same parameters had the opposite effect on mallard presence. The odds of black ducks being present were doubled where mallards were present, indicating that both species seem to be attracted to areas supporting adequate habitats, which contradicts the hypothesis of competition between these 2 species to explain for recent declines in the black duck population. Results of our habitat analyses support the hypothesis that habitat changes may be a primary factor leading to these declines. Dairy farm landscapes are of great importance for black ducks, and the conversion of this type of landscape toward a cropland landscape represents a threat to an important portion of the population of this species.