1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966

YEARS

FIGURE 5.-Duck breeding populations in North America, 1955-66 (adjusted for visibility bias and excludes scoters, eiders, mergansers and oldsquaw).

1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966

YEARS

FIGURE 6.-Mallard, pintail and blue-winged teal breeding population indexes, 1955-66 (adjusted for birds not recorded by the aerial crews).

1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966

YEARS

FIGURE 7.-Canvasback and redhead breeding population indexes, 1955-66 (unadjusted for birds not recorded by aerial crews).

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