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

Abstract

Capsule Both populations are increasing at a similar rate. Aims During 2000, an extensive survey of introduced Greater Canada Geese and re-established Greylag Geese in Great Britain was undertaken in order to update population estimates last made between 1988 and 1991. Methods A randomized stratified sample of 1329 of the 61 510 tetrads (2 km × 2 km unit) in Great Britain was surveyed. The habitat categories, or strata, were based on the proportion of water cover, urbanization, and upland/lowland in each tetrad. Non-urbanized strata were further divided into northern and southern reporting areas. Results In 2000 there were an estimated 88 866 full-grown Greater Canada Geese and 24 522 full-grown Greylag Geese in Great Britain. Since the 1988–91 survey, Greater Canada Geese have increased by 166% and Greylag Geese by 170%, an average per annum rate of increase of 9.3% for Greater Canada Geese and 9.4% for Greylag Geese. The increase in Greater Canada Goose numbers since the 1988–91 survey has occurred mainly in habitats which had previously held low goose population densities, particularly the ‘no water’ lowland habitat. Although densities were still relatively low in this habitat (<0.5 geese per km2), because of its extent it supported 56% of the total Greater Canada Goose population in 2000. The greatest increase in re-established Greylag Goose numbers has arisen from an expansion into lowland habitat with some water cover. Conclusion There was no obvious decline in the 8.3% per annum Greater Canada Goose growth rate that caused the population to treble between 1976 and 1991. Greylag Goose numbers are increasing at a similar rate to those of the Greater Canada Goose.