Since the 1975 publication of Waterfowl of North America, a great deal of ornithological literature has appeared concerning North American ducks, geese & swans. The most significant of these are the species accounts in the American Ornithologists’ Union The Birds of North America (B.O.N.A.) series, 46 of which were published between 1993 and 2003, and which include all the species known to breed in the United States and Canada (see references).
Population data of wild species are constantly changing, and sometimes of limited accuracy, but long-term averages or trends are often significant. National population surveys such as the annual U.S. Fish & Wildlife Service’s Breeding Bird Surveys, and annual hunter-kill (“harvest”) surveys by the U.S. Fish & Wildlife Service and Canadian Wildlife Service are thus of both immediate and long-term interest.
Text updates for the following species accounts are minimal. I have stressed apparent population trends and identified new major literature sources. I have also modified the majority of the range maps to make them more closely conform to our present-day knowledge of breeding and wintering ranges. The breeding ranges of some species are still inadequately known, such as those of the scoters, which breed in large regions of Canada and Alaska that are still only poorly surveyed. Not only have breeding ranges changed or become clearer, but also many wintering ranges have changed markedly since the 1970s, in conjunction with global warming trends (Johnsgard, 2009; Niven, Butcher & Bancroft, 2009).
Available at: http://works.bepress.com/paul_johnsgard/19/