Northern Prairie Wildlife Research Center
Most dabbling ducks are thought to breed as yearlings, most diving ducks as one- or two-year-olds, sea ducks and geese usually when two or three years old, and swans mostly at three years or older (Palmer 1976, Bellrose 1980). Among species that typically breed as yearlings, individuals hatched late in the breeding season may not breed until they are nearly 2 years old (e.g., Wood Duck, Gadwall; Bellrose 1980). For species that normally do not breed as yearlings, the date of hatching may not affect age of first breeding (Cooke, Findlay, and Rockwell 1984 for Snow Goose).
Male waterfowl attain sexual maturity at least as early as females (e.g., Wood 1964 for Canada Goose) but may breed first at an older age than females (e.g., Lesser Scaup, Bellrose 1980). This difference probably reflects the preponderance of males in many waterfowl populations (Bellrose et al. 1961, Aldrich 1973). Not all males can pair; younger males are often least likely to obtain a mate (Hori 1964, Blohm 1982), possibly due to their lower social status, inexperience, or poorer physical condition. In a contrasting population of Canada Geese in which females outnumbered males, males bred at earlier ages than females (Brakhage 1965).