Age-Class Determination of Canvasbacks

Influence of Ingested Lead on Body Mass of Wintering Canvasbacks

“…Length and width of head, culmen length and height, and keel length (?0.1 mm) were measured in the laboratory. Birds were categorized as hatch-year (HY = immature) or after-hatchyear (AHY = ad) based on plumage (Serie et al 1982) or cloacal characteristics (Hochbaum 1942). To the extent it was feasible, equal numbers of males and females, adults and immatures were shot.…”

Age Determination of American Black Ducks in Winter and Spring

“…Age determination using quantitative techniques requires limited prior experience (Serie et al 1982, Gatti 1983, Harvey at al. 1989) and is highly effective because it allows an objective corroboration of age estimates (e.g., Reynolds et al 1995).…”

“…This is especially important for the American black duck (Anas rubripes, hereafter black duck), a species of special concern in the North American Waterfowl Management Plan because of population declines in both the Atlantic and Mississippi Flyways (Canadian Wildlife Service and United States Fish and Wildlife Service 1986). Notwithstanding concern over the black duck decline (e.g., Feierbend 1984, Boyd and Hyslop 1985, Nichols 1991, Conroy et al 2002, no technique has been developed to separate age classes from late winter to late spring, as has been done with other species (e.g., blue-winged teal [A. discors], Dane 1968; redhead [Aythya americana], Dane and Johnson 1975;mallard [Anas platyrhynchos], Krapu et al 1979, Gatti 1983; canvasback [Aythya valisineria], Serie et al 1982; northern pintail [Anas acuta], Duncan 1985; and ringnecked duck [Aythya collaris], Hohman and Cypher 1986). Consequently, many key questions relating to how different black duck life-history characteristics vary by age have gone unanswered.…”