Editor’s Note (August 2016): Maps, rich media, and text have been updated to reflect a taxonomic change/split for this species. This species account is still being edited and may contain content from an earlier version of the account.
Suddenly out of the north came the sound I had been waiting for, a soft, melodious gabbling that swelled and died and increased in volume until all other sounds were engulfed by its clamor. Far in the blue I saw them, a long skein of dots undulating like a floating ribbon pulled toward the south by an invisible cord tied to the point of its V.
This harbinger of the changing seasons, so aptly described above by Sigurd F. Olson, is experienced each fall by naturalists across the continent. The Canada Goose is the most widely distributed goose in North America, and a characteristic species of the Nearctic avifauna. In North America, it breeds from eastern Labrador to western Alaska and is the only North American goose that commonly breeds south of 49°N. It occupies a broad range of habitats in temperate to low-arctic regions, including flat, featureless tundra; boreal forest; prairies and parklands; high mountain meadows; and a variety of managed refuge conditions and areas of human habitation. It nests individually or semicolonially, preferring sites on small islands in tundra lakes and ponds, and on margins of lakes, ponds, and rivers. On the breeding grounds, it forages primarily on grasses, sedges, and berries and in wintering areas on grasses and agricultural crops.
The Canada Goose exhibits marked morphological variation, perhaps the most extreme intraspecific differences in body size among birds, with subspecies that are among the largest and smallest of all geese. Within the species, there are trends in size from largest in the south to smallest in the north, and likewise in color from lighter in south and east, as well as in arid interior regions, to darker in the north and west; it has been demonstrated that variation in mensural characters occurs latitudinally within subspecies ( Leafloor and Rusch 1997 , A. Didiuk unpubl.). Despite decades of study ranging from detailed morphological analyses to molecular genetic techniques, the subspecific taxonomy of this species is still far from settled. Genetic studies have revealed, however, that 2 evolutionary groups may exist: one consisting of 7 primarily large-bodied subspecies and another of 4 small-bodied subspecies ( Quinn et al. 1991 , Baker and Marshall 1997 , Baker 1998 , Shields and Cotter 1998 ).
Breeders are monogamous, with life-long pair bonds formed usually during the second year. Offspring remain with their parents throughout the first year of life, traveling together in large flocks of family groups, as far south as Veracruz and Jalisco in south-central Mexico ( Saunders and Saunders 1981 ). Nineteen breeding units of Canada Geese are recognized for management purposes and what mixing occurs among individuals from different units is a result of pair formation away from the breeding grounds. Females are strongly philopatric, returning to the same breeding area each year; males may wander farther.
During spring and autumn migration, individuals concentrate at key staging and stopover areas, where they are particularly vulnerable to disease outbreaks and sport harvest. Nesting areas in the Arctic are secure for most populations, although oil and gas development places some groups at risk, and in some areas brood-rearing habitat of local migrant populations is being seriously degraded by increasing numbers of Lesser Snow Geese (Chen caerulescens caerulescens) and molt migrants from southern resident populations. Current population estimates range from between 3 million and 4 million individuals to as many as 8 million.
Efforts to re-establish the Giant Canada Goose in its native habitat in the midwestern United States have been so successful that many birds have been translocated from areas where high populations have become a nuisance to areas outside the original breeding range of the species. The result has been an expansion southward of the natural range that now includes areas of suitable habitat throughout the southern and southwestern United States ( Nelson and Oetting 1998 , Orr et al. 1998 ). Many of these populations have lost their migratory habit and have become established as permanent year-round residents in areas where they previously had occurred only in winter. The rapid increase of local breeding populations in many areas and subsequent mixing of resident birds with migrants during winter has resulted in uncertainty of origin and racial identity that has created a multitude of management problems and may threaten the diversity of the species across its entire range. Canada Goose populations in urban areas have been increasing during the past 50 years ( Conover 1998 ) and are currently a problem in more than 100 urban areas in 37 states, where their populations range in size from several hundred to more than 27,000 (for example, Minneapolis, Minnesota; Forbes 1998 ). Elucidating the biology of urban goose populations and developing management strategies for addressing the problems associated with their population buildup in urban/suburban environments is creating a new and difficult challenge for waterfowl biologists.
The biology of the Canada Goose has been studied extensively, especially those aspects related to population management. However, no long-term studies exist, so much remains to be learned. Recent studies on the genetics of subspecies ( Shields and Wilson 1987b , Van Wagner and Baker 1990 , Quinn et al. 1991 , Baker and Marshall 1997 , Baker 1998 , Shields and Cotter 1998 , Pierson et al. 2000 ) have helped clarify the taxonomy of this bird. Studies on the breeding grounds have contributed to our understanding of diet (Sedinger Sedinger 1984 , Sedinger 1986 , Sedinger 1992 , Sedinger 1997 ; Sedinger and Raveling Sedinger and Raveling 1984 , Sedinger and Raveling 1986 , Sedinger and Raveling 1988 , Sedinger and Raveling 1990 ; Reed et al. 1996a ), nesting requirements ( Cooper 1978b , Reese et al. 1987 , Bromley 1998 ), breeding biology ( Choudhury and Black 1993 , Drobney et al. 1999 ), brood-rearing behavior (Sedinger and Raveling Sedinger and Raveling 1988 , Sedinger and Raveling 1990 ; Bruggink et al. 1994 ; Fowler and Ely 1997 ; Didiuk and Rusch 1998 ; Jarvis and Bromley 2000 ), and reproductive success ( Brakhage 1965 , Hardy and Tacha 1989 , Moser and Rusch 1989 , Bromley and Jarvis 1993 , Sovey and Ball 1998 , Zenner and LaGrange 1998 , Raveling et al. 2000 ). Studies at staging areas, migratory-stopover sites, and wintering areas have clarified timing and routes of migration ( Raveling 1978b ; Wege and Raveling Wege and Raveling 1983 , Wege and Raveling 1984 ; Gill et al. 1996b ), food habits ( Bruggink et al. 1994 , Giroux and Bergeron 1996 , Gates et al. 2001 ), energetics (Sedinger et al. Sedinger et al. 1989 , Sedinger et al. 1995c ; Gates et al. Gates et al. 1998 , Gates et al. 2001 ), and detailed studies on vocalization and the importance of various aspects of vocal array in behavior (Whitford Whitford 1987 , Whitford 1996b , Whitford 1998 ). Studies such as those of Leafloor et al. ( Leafloor et al. 1998 ) on the influence of environmental factors on growth of goslings and ultimately the size of adults have been important in clarifying morphological differences among subspecies and the reliability of size differences in the intraspecific taxonomy of the species. The work of Abraham et al. ( Abraham et al. 1999 ) has aided understanding of the complex interactions between boreal and tundra breeding populations and expanding populations in temperate regions of the United States and southern Canada. Studies of urban-suburban populations have implicated Canada Goose feces in the eutrophication of small ponds and lakes, as well as the contamination of school yards, parks, and boating and swimming areas ( Conover and Chasko 1985 , Cooper and Keefe 1997 ), and the possibility of disease transmission to humans from direct contact with fecal material or contaminated water ( Conover and Chasko 1985 , Allan et al. 1995 , Cooper and Keefe 1997 , Feare et al. 1999 , Smith et al. 1999a ). We are beginning to understand the reproductive biology of urban-suburban populations with studies like those of Conover 1998 and Gosser and Conover 1999 , and are now applying management strategies based on their findings.