Snow Goose (Anser caerulescens)
This North American goose is a common migratory bird, breeding in Canada, Greenland, Alaska and the northernmost tip of Siberia and spending their winters in warmer regions of North America and into Mexico. It is a medium sized goose with a thin neck and stout bill and has two plumage colour morphs. The white morphs have white feathers everywhere except for black wing tips, and the blue morphs have a white head with a blue grey body. These two morphs can interbreed, although often geese will choose to mate with birds of the same colour morph. There are two subspecies of the snow goose:
- Anser caerulescens caerulescens or the lesser snow goose: this subspecies lives in Northern Canada through to the Bering straits region and is the slightly smaller of the two.
- Anser caerulescens atlanticus or the greater snow goose: this subspecies lives in Northern Canada, is the larger of the two and is less common.
The snow geese white morph (image from https://www.allaboutbirds.org/guide/Snow_Goose/id).
The snow geese blue morph (image from https://www.allaboutbirds.org/guide/Snow_Goose/id).
The snow goose is part of the family Anatidae, which is made up of species of water birds including ducks, geese and swans. Fossils of primitive geese from 10-12 million years ago have been found, part of a family called Vegaviddae, a group of waterfowl like birds that survived the extinction of the dinosaurs. Some prehistoric relatives of geese are estimated to have been 1 and a half feet tall!
Life on the go: migratory birds
A flock of geese in a huge, honking ‘V’ in the sky is a common sight. Snow geese spend half their year migrating to and from their wintering grounds, which generally tend to be coastal marsh areas in the United States. In recent years however, as human development shrinks available land, some populations of geese have moved inwards to agricultural land and this may be causing issues with crop growth and overgrazing of their tundra and salt marsh breeding grounds.
The two subspecies have different migratory routes; the greater snow goose travels along the Atlantic Flyway, a route that starts in Greenland and goes down the Atlantic coast of North America towards South America and the Caribbean. There are no mountain ranges for the bird to navigate around and good sources of food and shelter along the way. The lesser snow goose travels using several routes, including the Pacific Flyway (Alaska to Patagonia), the Mississippi flyway (Central Canada to the Gulf of Mexico following the Mississippi river) and the Central Flyway (Across the Great Plains to the Gulf of Mexico) to their wintering grounds on grasslands in the Gulf coastal plains. Here huge flocks forage together as families and use their stout beaks to dig up roots and tubers from the muddy marshes.
Snow geese do visit Europe occasionally, although more commonly they are escapes from private collections.
The major flyways used by migratory birds in North America. (image from 1000birds.com).
Snow geese form monogamous pairs usually in their second year, although they don’t begin to breed until they are three years old. The breeding season runs from May to June, with the geese couples engaging in dancing displays and vocalisations, foraging and nesting together. A clutch of eggs usually consists of 3-5 eggs which is incubated for 23-25 days while the male guards the nest.
Snow geese populations: too many fowl is foul?
Although snow geese numbers once plummeted in the early 20th century due to overhunting, today skyrocketing populations (increasing by 5% per year!) are beginning to cause issues. Currently listed as least concern by the IUCN and with populations increasing, huge flocks of geese are reaching areas previously untouched by such large numbers of birds, and in the 1990’s it was officially recognised that the birds were causing huge issues in their wintering grounds, stripping vegetation, and causing significant damage to arctic and sub-arctic tundra. Their feeding strategy is particularly troublesome, as pulling up vegetation with their beaks can destroy root structures and damage habitats for years, preventing regrowth, with researchers in the Hudson Bay area determining it can take up to ten years for a tundra destroyed by geese to recover. Not only is their impact on their habitat serious, but this degradation has a significant impact on other species, including other waterfowl and any animals that use the tundra as their home. As a result, laws regarding snow goose hunting were relaxed, allowing people to take a larger quota of geese as they travelled to and from their wintering grounds. Although hunting is unpalatable, it may be an unfortunate necessity in controlling the damage the rapidly increasing snow goose population is doing.
The huge flocks of snow geese that are damaging their tundra breeding grounds. (image from americanornithology.com).
Awesome videos!
References
Admundson, C.L. Flint, P.L. Stehn, R.A. Platte, R.M. Wilson, H.M. Larned, W.W. and Fischer, J.B. (2019) ‘Spatio-temporal population change of Arctic breeding waterbirds on the Arctic coastal plain of Alaska.’ Avian Conservation and Ecology, 14(1)
https://www.rspb.org.uk/birds-and-wildlife/wildlife-guides/bird-a-z/snow-goose/
https://www.allaboutbirds.org/guide/Snow_Goose/id
https://animalia.bio/snow-goose
Kear, J. (2005) ‘Ducks, geese and swans volume 1’. Oxford University Press.
