Snow Goose Anser caerulescens Scientific name definitions

Upon approach you could be forgiven for thinking the field to be full of tightly packed sheep. Until, that is, your ears overflow with the clamor of ten thousand conversing geese. The chatter beckons to you, surrounds you, subsumes you. Until, suddenly, all is silence, as if silence itself was a sound, a striking sound demanding attention. For one, two, three seconds .. the quiet is absolute .. and then a cacophony erupts as geese hurl themselves into mad flight, a rising blizzard circling ever higher before shearing apart into strings destined for the horizon as the dark menace of a hungry eagle approaches.

― the author's (SGM) reflections on Snow Geese in tulip fields of Washington's Skagit Delta.

The Snow Goose (Anser caerulescens)is one of the most abundant species of waterfowl in the world, breeding in large and often dense colonies north of the tree line from extreme northeastern Russia, along the coast and islands of arctic North America to northwestern Greenland. The species is composed of three fairly discrete regional breeding and wintering populations—western, midcontinent, and eastern—with birds migrating from breeding to wintering grounds and back along roughly parallel lines of longitude, and each flock using similar staging and stopover areas during migration. Migrating and wintering birds often congregate in very large flocks. The largest wintering populations occur in northern and central California (western), from Missouri and Arkansas to coastal Texas and Louisiana (midcontinent), and along the Atlantic Coast from New Jersey to North Carolina (eastern), with smaller numbers gathering from southern California southeast to northern Mexico and northeast through southeastern Colorado to central Kansas as well as along the Atlantic Coast north to New York and south to Georgia. Together, the western and midcontinent populations form the subspecies known as the Lesser Snow Goose, A. c. caerulescens, while the eastern population forms the Greater Snow Goose, A. c. atlantica.

The species is dimorphic, consisting of a white morph and a dark morph (frequently called a blue morph, blue phase, or "Blue Goose"), with some intermediates. The color morph is controlled by a single gene locus where the dark allele is incompletely dominant to the white. The distribution of color morphs is unequal in the population, with the maximum number of dark morph geese occurring in midcontinent breeding and wintering areas. The nesting colonies of dark morph geese were not discovered until 1929 after an astonishing direct and intentional search by Dewey Soper that lasted six years and covered 30,300 miles (1 Soper, J. D. (1930). Discovery of the Breeding Grounds of the Blue Goose. Canadian Field Naturalist 44:1-11. Close ). Light and dark morph Snow Geese remained relatively allopatric in distribution until approximately 1930, but since then, sympatry has led to gene flow, and gene flow has resulted in the current pattern of color frequencies (2 Cooke, F., R. F. Rockwell, and D. B. Lank (1995). The Snow Geese of La Pérouse Bay: Natural Selection in the Wild. Oxford University Press, Oxford, UK. Close ). Until 1983, the two color morphs were considered separate species (3 American Ornithologists' Union (1983) Check-list of North American Birds. Sixth edition. American Ornithologists' Union, Washington, DC, USA. Close ). Structural size in the Snow Goose has been shown to be highly variable and dependent on growth conditions during the prefledging period (4 Cooch, E. G., D. B. Lank, A. Dzubin, R. F. Rockwell and F. Cooke. (1991a). Body size variation in Lesser Snow Geese: environmental plasticity in gosling growth rates. Ecology 72:503-512. Close , 5 Lepage, D., G. Gauthier and A. Reed. (1998a). Seasonal variation in growth of Greater Snow Goose goslings: the role of food supply. Oecologia 114:226-235. Close ), which implies that body size may not be a reliable indicator of subspecies.

The Snow Gooseis a voracious forager, feeding for sustained periods of time in concentrated areas; females forage up to 50% of the day during spring migration and up to 75% on breeding grounds before nesting. On the wintering grounds, the Snow Goose often feeds in very large flocks in restricted areas. Its diet consists entirely of plant material, and the primary foraging strategy involves grubbing for underground rhizomes, tubers, and roots, but Snow Geese also graze on tender new shoots of aquatic and agricultural plants and actively scavenges agricultural fields for waste grain. As this species has taken advantage of previously unavailable sources of food during migration and winter, its population has increased rapidly—in some areas, as much as 9% per year (6 Gauthier, G. and S. Brault. (1998). "Population model of the Greater Snow Goose: projected impacts of reproduction in survival on population growth rate." In The Greater Snow Goose: report of the Arctic Goose Habitat Working Group., edited by B. D. J. Batt, 65-80. Ottawa, ON: Arctic Goose Joint Venture Spec. Publ. U.S. Fish Wildl. Serv., Washington, D.C., and Can. Wildl. Serv. Close ). A greatly increased population, coupled with its primary foraging strategy of grubbing, is causing serious damage to its habitat in breeding and, more locally, wintering areas. Current estimates place its population at 14 million (7 U.S. Fish and Wildlife Service (2019). Waterfowl population status, 2019. U.S. Department of the Interior, Washington, DC, USA. Close ), a number that may be environmentally unsustainable.

This species is socially monogamous, with life-long pair bonds usually formed away from the breeding grounds during the second year of life. During the breeding season, the Snow Goose is aggressively territorial, with pairs defending an area of variable size around their nest site; during non-breeding season, it is highly gregarious. The family unit is strong, with goslings remaining with their parents until mate selection during their second or third year. Mating is assortative by size and color morph, with members of dimorphic populations actively choose mates according to the morph of the family in which they were raised. As females are strongly philopatric, returning to the same breeding colony each year, there is little movement of females among colonies, but there is considerable movement of males.

The Snow Goose is one of the better studied avian species in North America. Excellent intensive, long-term studies of breeding colonies, such as that at La Pérouse Bay, Manitoba (2 Cooke, F., R. F. Rockwell, and D. B. Lank (1995). The Snow Geese of La Pérouse Bay: Natural Selection in the Wild. Oxford University Press, Oxford, UK. Close ), have given us a unique synthesis of its biology. Other studies on the breeding grounds have also contributed to our understanding of its food habits (8 Gauthier, G. and J. Tardif. (1991). Female feeding and male vigilance during nesting in Greater Snow Geese. Condor 93:701-711. Close , 9 Gauthier, G. (1993b). Feeding ecology of nesting Greater Snow Geese. Journal of Wildlife Management 57:216-223. Close , 10 Gadallah, F. L. and R. L. Jefferies. (1995). Forage quality in brood rearing areas of the Lesser Snow Goose and the growth of captive goslings. Journal of Applied Ecology 32:276-287. Close ), nesting requirements (11 Alisauskas, R. T., and H. Boyd (1994). Previously unrecorded colonies of Ross' and Lesser Snow Geese in the Queen Maud Gulf Bird Sanctuary. Arctic 47:69-73. Close , 12 Hughes, R. J., G. Gauthier and A. Reed. (1994a). Summer habitat use and behaviour of Greater Snow Geese A. caerulescens. Wildfowl 45:49-64. Close , 13 Ganter, B. and F. Cooke. (1998). Colonial nesters in deteriorating habitat: site fidelity and colony dynamics of Lesser Snow Geese. Auk 115:642-652. Close ), breeding biology (14 Davies, J. C. and F. Cooke. (1983b). Intraclutch hatch synchronization in the Lesser Snow Goose. Canadian Journal of Zoology 61:1398-1401. Close , 15 Davies, J. C. and F. Cooke. (1983a). Annual nesting productivity in Snow Geese: prairie drought and arctic springs. Journal of Wildlife Management 47:291-296. Close , 16 Lank, D. B., E. G. Cooch, R. F. Rockwell and F. Cooke. (1989a). Environmental and demographic correlates of intra-specific nest parasitism in Lesser Snow Geese. Animal Behaviour 37:74-89. Close , 17 Lank, D. B., P. Mineau, R. F. Rockwell and F. Cooke. (1989b). Intraspecific nest-parasitism and extra-pair copulation in Lesser Snow Geese. Animal Behaviour 37:74-89. Close , 18 Schubert, C. A. and F. Cooke. (1993). Egg-laying intervals in the Lesser Snow Goose. Wilson Bulletin 105:414-426. Close ), brood-rearing behavior (19 Mulder, R. S., T. D. Williams and F. Cooke. (1995). Dominance, brood size and foraging behavior during brood-rearing in the Lesser Snow Goose: an experimental study. Condor 97:99-106. Close ), and reproductive success (20 Hamann, J., B. Andrews and F. Cooke. (1986). The role of follicular atresia in inter- and intra-seasonal clutch size variation in Lesser Snow Geese (Anser caerulescens caerulescens). Journal of Animal Ecology 55:481-489. Close , 21 Hamann, J. and F. Cooke. (1987). Age effects on clutch size and laying dates of individual females in Lesser Snow Geese. Ibis 129:527-532. Close , 22 Rockwell, R. F., E. G. Cooch, C. B. Thompson and F. Cooke. (1993). Age and reproductive success in female Lesser Snow Geese: experience, senescence and the cost of philopatry. Journal of Animal Ecology 62:323-333. Close , 23 Viallefont, A., F. Cooke and J. D. Lebreton. (1995). Age specific costs of first time breeding. Auk 112:67-76. Close , 24 Lepage, D. G., G. Gauthier and S. Menu. (2000). Reproductive consequences of egg-laying decisions in Snow Geese. Journal of Animal Ecology 69:414-427. Close ). Studies at staging areas, migratory-stopover sites, and on the wintering grounds have clarified timing and routes of migration (25 Alisauskas, R. T. and C. D. Ankney. (1992a). Spring habitat use and diets of midcontinent adult Lesser Snow Geese. Journal of Wildlife Management 56:43-54. Close , 26 Francis, C. M. and F. Cooke. (1992a). Migration routes and recovery rates of Lesser Snow Geese from southwestern Hudson Bay. Journal of Wildlife Management 56:279-286. Close , 27 Maisonneuve, C. and J. Bédard. (1993). Distribution and movements of Greater Snow Geese, Chen caerulescens atlantica, during fall staging in the St. Lawrence estuary, Quebec. Canadian Field-Naturalist 107:305-313. Close , 28 Baranyuk, V. V. and J. Y. Takekawa. (1998). Migration of the Snow Geese in Chukotka and St. Lawrence Island. Casarca 4:169-187. Close ) and food habits (29 Gauthier, G., J. Bédard, J. Huot and Y. Bédard. (1984b). Spring accumulations of fat by Greater Snow Geese in two staging habitats. Condor 86:192-199. Close , 30 Gauthier, G., J. Bédard, J. Huot and Y. Bédard. (1984a). Protein reserves during staging in Greater Snow Geese. Condor 86:210-212. Close , 31 Gauthier, G., J. F. Giroux and J. Bédard. (1992b). Dynamics of fat and protein reserves during winter and spring migration in Greater Snow Geese. Canadian Journal of Zoology 70:2077-2087. Close , 32 Davis, S. E., E. E. Klaas and K. J. Koehler. (1989). Diurnal time-activity budgets and habitat use of Lesser Snow Geese Anser caerulescens in the middle Missouri River Valley during winter and spring. Wildfowl 40:45-54. Close , 33 Bélanger, L. and J. Bédard. (1995). Use of ice-scoured depressions by marsh-foraging Snow Geese (Chen caerulescens atlantica). Canadian Journal of Zoology 73:253-259. Close , 34 Ballard, B. M. and T. C. Tacha. (1995). Habitat use by geese wintering in southern Texas. Southwestern Naturalist 40:68-75. Close , 35 Boyd, W. S. (1995). Lesser Snow Geese (Anser caerulescens) and American three-square bulrush (Scirpus americanus) on the Fraser and Skagit River Deltas. Ph.D. thesis, Simon Fraser Univ., Burnaby, BC. Close , 36 Robertson, D. G., A. W. Brackney, M. A. Spindler and J. W. Hupp. (1997a). Distribution of autumn-staging Lesser Snow Geese on the Northeast Coastal Plain of Alaska. Journal of Field Ornithology 68:124-134. Close ). The genetics underlying color dimorphism in this species has been elucidated (37 Cooke, F. and F. G. Cooch. (1968). The genetics of the polymorphism in the goose Anser caerulescens. Evolution 22:289-300. Close , 38 Rattray, B. and F. Cooke. (1984). Genetic modelling: an analysis of a colour polymorphism in the Snow Goose (Anser caerulescens). Zool. J. Linn. Soc. 80:437-445. Close , 39 Mundy, N. I., N. S. Badcock, T. Hart, K. Scribner, K. Janssen, and N. J. Nadeau (2004). Conserved genetic basis of a quantitative plumage trait involved in mate choice. Science 303:1870–1873. Close ), as has spatial and temporal variation in color (40 Avise, J. C., R. T. Alisauskas, W. S. Nelson, and C. D. Ankney (1992). Matriarchal population genetic structure in an avian species with female natal philopatry. Evolution 46:1084–1096. Close , 41 Quinn, T. W. (1992). The genetic legacy of mother goose-phylogeographic patterns of Lesser Snow Goose Chen caerulescens caerulescens maternal lineages. Molecular Ecology 1:105-117. Close ). Because of the flocking behavior on the wintering grounds and during migration, however, we still do not know how or exactly when mate selection occurs. We also lack vital information about the timing and location of molt in some populations and the molting process in general, and, although a highly vocal species, we know little about how vocalization develops and the context of various vocalizations.