The effect on the environment of Great Britain's naturalized Greater Canada Branta canadensis and Egyptian Geese Alopochen aegyptiacus

Greater Canada and Egyptian Geese are amongst the most abundant introduced bird species in Great Britain, both numerically and by biomass. Both species have increased rapidly in numbers and range within Great Britain. Greater Canada Goose numbers have increased by over 8% per annum since 1962. Although estimates of Egyptian Goose numbers are less reliable, in 2000 there were more than twice as many individuals of this species in Great Britain than in the early 1980s. The population growth of both species is showing no sign of slowing down. The species have been recorded as being aggressive towards native species of waterbird, to hybridize with native species of waterbird, to cause water eutrophication, to be agricultural pests and to pose an aircraft birdstrike risk. However, much of the evidence that these species affect the environment and native species is anecdotal or in grey literature that has not been peer-reviewed. We argue that there is a clear need for more work to assess the effects of non-native species on the environment, and that the Greater Canada Goose would be a particularly good model species for research on non-native species more generally.