Invasion history: Branta canadensis, Canada Goose
Origin Canada geese are very widely distributed across their native range in North America, from Alaska to West Greenland southwards across Canada and the USA. They are winter visitors to southern most USA and northern Mexico, and vagrants to Central America, the Caribbean, western Europe and eastern Asia.
First Record Canada geese were first introduced to St James’s Park in London in 1665 (or earlier), beginning a fashion for wealthy landowners to import this species as an ornament to park lakes. They have been established since at least 1731.
Pathway and Method New importation from North America, and translocations within GB, were the main sources of Canada geese in GB for more than 200 years. Since then, there has been a slow natural spread, aided by further translocations, which has accelerated greatly in recent decades.
Species Status As recently as 1953 there were fewer than 4000 birds in GB, in isolated groups. But by the late 1980s there were more than 50,000. The GB population increased at a rate estimated at 9.3% per annum between 1988 91 and 2000, with no sign of the rate of increase slowing, raising the population to around 89,000. Further non native populations are scattered across Europe from Ireland to Finland and the Ukraine, and are found also in New Zealand.
Ecology Habitat: Branta canadensis, Canada Goose
Dispersal Mechanisms Canada geese are mostly migratory in the native range but GB birds show no southward tendency in winter. Some birds in central England established a moult migration to northern Scotland. Ring recoveries show considerable interchange between sites and have also linked GB populations with those in the Faeroes, Norway, Sweden and even western Siberia.
Reproduction Canada geese lay a single clutch of 5 7 eggs. They vigorously defend a small area around their nest against predators, threatening and even attacking human intruders. Chicks from neighbouring nests may form large crches, guarded by their parents or other adults.
Known Predators/Herbivores The species has few predators. Adults occasionally fall victim to foxes.
Resistant Stages None known.
Habitat Occupied in GB Flocks of Canada geese can be expected around any fresh water body in GB, especially where there are suitable grazing sites. Urban and suburban as well as rural sites are occupied.
Impacts: Branta canadensis, Canada Goose
Environmental Impact Introduced geese are heavy grazers of aquatic and waterside vegetation, and their droppings can increase nutrient levels in water bodies and soils. Trampling and the addition of nutrients can change the composition of plant communities, especially where grazing is intense.
Health and Scoial Impact There is considerable concern that the presence of so many large birds in close association with people, for example in urban parks, may be a health hazard. Canada geese are suspected of transmitting Salmonella to cattle. The presence of slippery droppings can be a nuisance, especially on paths, playing fields or golf courses, as can possible aggression from nesting adults. Bird strikes involving Canada geese have caused human deaths and injury as well as damage to the environment and loss of or damage to aircraft.
Economic Impact Canada geese may graze on farmland at any season, occur very widely, and may feed in areas that would be shunned by wild geese. Their grazing and trampling may cause major damage to grassland and crops. Birds climbing out from the water to graze make shallow, well trodden paths that can damage flood defences and accelerate bankside erosion.
References Links: Branta canadensis, Canada Goose
Identification Svensson, L., Mullarney, K. Zetterstrm, D. (2010) Collins Bird Guide. Second edition. HarperCollins, London. (2007) Population size and differential population growth of introduced Greater Canada Geese Branta canadensis and re established Greylag Geese Anser anser across habitats in Great Britain in the year 2000. Bird Study, 54, 343 352. (eds) (2013) Bird Atlas 2007 11: the breeding and wintering birds of Britain and Ireland. BTO Books, Thetford. (1985) Natal and breeding dispersal of Canada geese Branta canadensis. Ibis, 127, 31 41.