Invasies van de Kleine Alk Alle alle: voorkomen en achtergronden

The wintering range of Little Auks Alle alle breeding in the northern North Atlantic extends from the southern border of the pack ice zone, to the northern North Sea in the east and the Grand Banks off Newfoundland in the west. Occasionally, large scale southward movements occur into more temperate waters of the North Atlantic region, with small numbers reaching Spain, the Azores and the Florida Keys. Since 1840, at least 63 influxes were reported in Europe and another 27 in North America (Table I). In the East Atlantic some clustering of years with large numbers is obvious, but in the West (with perhaps slightly poorer data) such a clustering was not found. Influxes in the West and the East Atlantic did not occur simultaneously. The origin of Little Auks wintering off Newfoundland is probably NW Greenland, whereas birds nesting on Svalbard at least partly migrate to SW Greenland. The origin of nearly one million wintering Little Auks in the North Sea is fully unknown. A first step towards a better understanding of the wintering distribution of Little Auks could be the collection of biometrical data in all pans of the breeding and wintering range. A reconstruction of possible migration routes is given in figure 3. Influxes and wrecks of Little Auks often occurred during or immediately following severe storms, which has led to speculations that the birds were simply blown ashore. However, it has been suggested that influxes are in fact triggered by prolonged periods of food shortages or reductions in the availability of prey in ’normal’ wintering areas. Because in the most spectacular influxes only a few tens of thousands Little Auks are involved, and because there appears to be no relation between influxes on either side of the Atlantic, the wrecks may reflect local problems of patches of wintering Little Auks rather than severe problems for significant parts of the Atlantic wintering population. Coastal observations suggest an increase of wintering Little Auks in the North Sea since the mid-1980s. These results suggest that highly variable numbers of Little Auks use the North Sea as a wintering area.