Geografische variatie bij ganzen Deel 10 (slot) De Sneeuwgans Anser caerulescens en de Ross’ Gans Anser rossii

The Snow Geese (A. c. caerulescens, A. c. atlanticus and A. rossii) are mainly breeding in the arctic regions of North America. They are also wintering in inland haunts and in the coastal areas of Atlantic and Pacific North America. To a certain extent, some small populations are also occurring in restricted parts of Northeastern Siberia and there is strong evidence that, about one century ago, Lesser Snow Geese were breeding at least in the Lower Lena region and likely even in the easternmost part of the Taimyr Peninsula, wintering by that time in the Caspian region, along the Black Sea coast of Turkey and even in the Greek archipelago in the Mediterranean. Although the first observations of ‘Snow Geese’ in The Netherlands were reported already in the early 1890s, it lasts until the second half of the 20th century until these geese became regular winter visitors in some numbers, especially during severe cold winters. But these geese were not necessarily originating from wild stocks, as was proven by the appearance of a flock of eightteen Snow Geese near Maarssen, province of Utrecht, on February 21/22th 1947, of which one bird was ringed in the feral stock of Bengt Berg in Sweden. However, another flock of 18 birds, seen on April 20th 1980 near Andijk, province of Noord-Holland, contained one gander that was ringed as a young gosling in the La Perouse Bay colony of the Hudson Bay region during the breeding season of 1977. That first observation proved undoubtedly that wild birds from the nearctic populations are able to spontaneously reach Western Europe in some cases. During the last decades of the 20th century, also increasing but still small numbers of Blue Snow Geese were regularly seen in The Netherlands. This seems to indicate that it is possible that these could have been wild birds from the nearctic breeding stock. On the other hand, since 1961 a breeding project is going on in the Askania Nova Nature Reserve in Southern Ukraine and from geese ringed in that area recoveries were already collected from France, Poland, Finland and Norway. Flence it seems not unlikely that at least some of the geese seen in The Netherlands were originating from that project too. Apart from the Lesser Snow Goose A. caerulescens only very few Greater Snow Geese A. atlanticus seems to visit The Netherlands, but recently there are increasing observations of Ross’ Geese, probably as a result of the increasing breeding stock in North America.