Snow geese are large white geese that breed in colonies in the Arctic tundra of Canada, Alaska, and Siberia. They migrate long distances in large flocks to spend the winter in more southerly parts of North America. Snow geese are herbivores that graze on grasses, sedges, berries, and agricultural crops during migration and on their wintering grounds. However, their main prey items consist of plant foods found on their Arctic breeding grounds.
Plant Foods Eaten by Snow Geese
On their breeding grounds, snow geese primarily eat leaves, roots, stems, and seeds of wetland plants. Their diet consists mainly of:
- Sedges – Several sedge species, especially cotton grasses
- Grasses – Saltgrass, alkali grass, fowl bluegrass
- Rushes – Leafy vegetation and seeds of several rush species
- Horsetails – Stems and shoots of horsetail plants
- Pondweeds – Leaves and stems of pondweed plants
Snow geese feed extensively on cotton grasses while on their breeding grounds. The leaves, roots, and stems of cotton grasses provide the main source of nutrients for adult geese during egg laying and incubation. Cotton grass seeds are also eaten in large quantities by goslings once they hatch.
In salt marsh breeding habitats, snow geese consume large amounts of saltgrass and alkali grass. They graze heavily on the lush grass growth stimulated by nitrogen-rich goose droppings around colony sites. Rushes, sedges, and pondweeds growing in wet meadows and freshwater pools are also important summer foods.
On their staging areas during spring migration, snow geese eat waste barley, wheat, and oats in agricultural fields, as well as early growth of grasses and sedges. New green growth of sedges, grasses, and horsetails are consumed when the geese arrive on the Arctic breeding grounds.
Protein and Mineral Sources
Snow geese get most of their protein from the leaves, stems, and seeds of wetland plants during the breeding season. However, they also consume some animal matter to obtain more protein, minerals, and nutrients:
- Aquatic insects – Snow geese eat mosquito and midge larvae, caddisflies, dragonflies, beetles.
- Crustaceans – Fairy shrimp, clam shrimp, water fleas, seed shrimp.
- Mollusks – Small snails and freshwater clams.
- Fish eggs – Eggs of capelin, arctic char,ciscoes, and sticklebacks.
They feed on these small aquatic invertebrates and fish eggs by dabbling and tipping up in shallow tundra pools, lake margins, and tidal flats. The protein and minerals obtained from these animal foods are especially important for gosling growth and development.
Agricultural Crops
During fall migration and winter, snow geese rely heavily on waste corn, wheat, rice, and soybeans in agricultural fields. They consume large quantities of these cereal grains and legumes on migration stopovers and wintering areas across the Great Plains, Midwest, Mississippi Delta, and Pacific Flyway.
Snow geese cause extensive damage to crops by grazing on emerging winter wheat and rye. They also glean waste corn and soybeans from harvested fields, depleting the food resources needed by other wildlife during winter.
Differences Between Lesser and Greater Snow Geese
The dietary preferences of the two subspecies of snow goose differ slightly:
Lesser snow geese
- Prefer grazing on grasses and sedges
- Eat more green vegetative parts
- Consume more aquatic plants
- Do more grazing and less rooting than greater snows
Greater snow geese
- Prefer sedges over grasses
- Eat more seeds, roots, and rhizomes
- Consume more agricultural crops
- Rooting destroys marsh veg more than grazing
In general, lesser snow geese tend to be more vegetarian, feeding more heavily on grasses, leafy plants and their seeds. Greater snow geese eat more underground plant parts such as roots, rhizomes, and bulbs by grubbing and rooting in the soil.
Feeding Ecology
Snow geese have diverse adaptations for feeding on different types of wetland vegetation:
- Dabbling – Tilt head underwater to eat pondweeds and aquatic insects.
- Grazing – Clip off grass blades and sedges with serrated edges of bill.
- Grubbing – Dig roots and rhizomes from soil with strong neck and bill.
- Seed eating – Crack hard seeds of sedges, grasses, rushes open with muscular gizzard.
Their short, thick necks and strong bills are well-suited for grubbing underground plant parts. Snow geese also have several anatomical adaptations for efficiently digesting high-fiber plant material including a large hindgut and microbial fermentation in the cecum.
On their staging and wintering grounds, snow geese exhibit natural daily rhythms of feeding activity:
- Early morning – Feed actively in fields.
- Late morning – Loaf and rest in wetlands.
- Afternoon – Return to feed in fields.
- Early evening – Return to wetlands to roost.
This circadian pattern matches the timing of their digestive system and allows for optimal nutrient absorption from their vegetarian diet.
Impacts on Vegetation
Snow geese exert strong grazing pressure on Arctic plant communities. Some major impacts include:
- Overgrazing sedges and grasses around colonies.
- Erosion around grubbing sites.
- Spread of goose droppings leads to fertilization.
- Grazing stimulates growth of unpalatable grasses.
- Degraded areas are colonized by invasive species.
The grubbing and uprooting of vegetative cover by geese results in erosion of peat banks along lakeshores. Overgrazed areas are subject to invasion by unpalatable or weedy grass species. Goose droppings increase fertility, but grubbing damages the retention of nutrients in the ecosystem.
High densities of staging snow geese also deplete agricultural crops. Estimated losses of $5-10 million annually are caused during migration. Measures to reduce snow goose overpopulation help alleviate grazing damage to natural salt marsh and agricultural habitats.
Diet Studies
The diet composition of snow geese has been extensively studied by analysis of:
- Crop and esophageal contents – Samples from hunter-killed geese.
- Feces – Microhistological analysis of plant epidermal tissues.
- Stable isotopes – Ratios of carbon and nitrogen isotopes in goose tissues.
- Behavioral observations – Of feeding activity in different habitats.
These techniques identify the types of plants and relative amounts of each plant species consumed. Results help determine key food resources used at different stages of the yearly cycle.
For example, Table 1 summarizes a study of lesser snow goose diets on the Yukon-Kuskokwim Delta of Alaska during the brood-rearing period based on fecal analysis (Sedinger and Raveling 1984):
Plant Species | Percent Composition of Diet |
---|---|
Carex subspathacea | 41% |
Carex ramenskii | 19% |
Puccinellia phryganodes | 13% |
Other Sedges | 9% |
Dupontia fischeri | 6% |
Other Grasses | 3% |
Other Plants | 9% |
The sedges Carex subspathacea and Carex ramenskii together made up 60% of the goslings’ diet. Cotton-grass sedges are very important foods for snow geese during the summer months on the tundra breeding grounds.
Summary
In summary, the key prey items and feeding habits of snow geese include:
- Primary summer foods are leaves, stems, roots of sedges, grasses, rushes.
- Also eat horsetails, pondweeds, mosquito larvae, crustaceans, mollusks.
- Rely on agricultural crops like corn, wheat, soybeans during migration and winter.
- Differ in proportions of grasses vs. sedges and plant parts consumed.
- Have specialized adaptations for grazing, grubbing, and dabbling.
- Can damage tundra vegetation through overgrazing, grubbing, fertilization.
- Diet determined by analysis of gut contents, feces, stable isotopes.
In conclusion, snow geese are almost entirely herbivorous, feeding chiefly on sedges, grasses, and agricultural grains. Their specialized adaptations allow them to exploit various plant foods in wetland habitats across North America throughout their extensive annual migrations.
References
Sedinger, J.S. and Raveling, D.G. (1984). Dietary selectivity in relation to availability and quality of food for goslings of cackling geese. The Auk, 101(2), pp.295-306.
Mowbray, T.B., Cooke, F. and Ganter, B. (2000). Snow goose (Chen caerulescens). In: Poole, A. and Gill, F. (eds.). The Birds of North America, No. 514. Philadelphia, PA: The Birds of North America Inc.
Fox, A.D. and Madsen, J. (2017). Threatened species to super-abundance: The unexpected international implications of successful goose conservation. Ambio, 46(Suppl 2), pp.179-187.
Whyte, R.J. and Bollinger, E.K. (1985). Depletion of agricultural crops by migrating geese in the northern part of the interior valley of California. Arctic geese. Proceedings of a symposium held at the 40th Midwest Fish and Wildlife Conference. pp.240-245.