Latitudinal-Related Variation in Wintering Population Trends of Greylag Geese (Anser Anser) along the Atlantic Flyway: A Response to Climate Change?

摘要

The unusually high quality of census data for large waterbirds in Europe facilitates the studyudof how population change varies across a broad geographical range and relates to globaludchange. The wintering population of the greylag goose Anser anser in the Atlantic flywayudspanning between Sweden and Spain has increased from 120 000 to 610 000 individualsudover the past three decades, and expanded its wintering range northwards. Although populationudsizes recorded in January have increased in all seven countries in the winteringudrange, we found a pronounced northwards latitudinal effect in which the rate of increase isudhigher at greater latitudes, causing a constant shift in the centre of gravity for the spatial distributionudof wintering geese. Local winter temperatures have a strong influence on gooseudnumbers but in a manner that is also dependent on latitude, with the partial effect of temperatureud(while controlling for the increasing population trend between years) being negative atudthe south end and positive at the north end of the flyway. Contrary to assumptions in the literature,udthe expansion of crops exploited by greylag geese has made little contribution toudthe increases in population size. Only in one case (expansion of winter cereals in Denmark)uddid we find evidence of an effect of changing land use. The expanding and shifting greylagudpopulation is likely to have increasing impacts on habitats in northern Europe during theudcourse of this century.