Winter appraisals of annual productivity in geese and other water birds

Abstract

Every nestling season stamps a visible record of its success or failure on fall populations of geese, swans, and some other water birds. Thanks to the distinctive first winter colouration of young of some species, and the persistence of broods ('families') and other functional groupings in some of these and other species, comprehensive studies of annual reproductive success and mortality can be made by methodical field scanning of wintering flocks. Winter survey methods developed for Blue, Snow and White-fronted Geese are discussed here in great detail, not only because of their intrinsic importance, but because they may provide clues for probing the vital statistics of other birds. Winter appraisals of productivity have the special advantages of being quick, simple and economical, and of providing information that is timely rather than historical. Their efficacy hinges upon competence of field observers. So long as observers remain afield the appraisals can take cognizance of biological as well as arithmetical aspects of current welfare of populations. By themselves the data from some winter appraisals may be sufficient for routine management of the robust species; used in concert with other surveys they may help solve many intricate problems in those bird populations that require special attention.