Reproductive variables of American black ducks along the St. Lawrence estuary, 1963-1991

Abstract

We examine data from different surveys conducted from 1963 to 1991 in the Baie de l’Isle Verte National WildlifeArea and the surrounding offshore islands, an approximately 20-km2 coastal segment of the St.Lawrence estuary in Quebec.We summarize data regarding various aspects of the nesting ecology of the American black duck (Anas rubripes) (n = 812nests). Mean laying date, average clutch size, and apparent nesting success did not differ among years (P > 0.05). Black ducksnested earlier on islands (mean Julian date 120.0 vs. 121.3;P = 0.03), but mean clutch size and nesting success on islands didnot differ from those on the mainland (P> 0.05). Among mainland-nesting black ducks, those nesting in mixed stands of treesand bushes initiated nests almost 10 days earlier than those nesting in the two other types of nest cover (mean Julian date 124.0vs. 134.4 and 139.6). Black ducks nesting in such habitats as woodlots, peat bogs, or shrubland laid a larger number of eggsthan those nesting in the two other habitat types (mean 9.7 vs. 8.8 and 9.4). Finally, we observed that nesting success of ducksnesting in woodlots, peat bogs, and shrubland and in mixed stands of trees and bushes or of herbaceous plants and shrubs wasup to three times higher than at other sites (P<= 0.05). We conclude that in addition to protection and restoration of existingislands, more emphasis should be placed on conserving peat bogs, coniferous woodlots, and shrubland, because they alsoconstitute good mainland-nesting habitat for black ducks along the St. Lawrence estuary.