Geografische variatie bij Ganzen Deel 3 De West-Siberische Taigagans of Johansens Gans Anser fabalis johanseni
Het Vogeljaar , Volume 51 - Issue 2 p. 58- 64
In this paper a description of the West Siberian Taiga Bean Goose Anser fabalis johanseni is given. This bird differs from specimens of the nominate-race Anser fabalis fabalis (‘Yellow-billed Goose’) not only by a bigger size of the body, a longer neck and the typical pattern on the bill, which shows usually only a narrow orange band between the nail and the nostrils, while the structure of the bill is more slender and thinner than it usually is in fabalis. Specimen of the typical johanseni-type seldom have some white feathers at the base of the bill, a characteristic that on the other hand is found in almost all birds of the pure nominate race. When observed in the field johanseni is a very dark, large, slender bird with a long neck and a straight, dark bill with only a narrow orange band directly behind the nail at the very top of both upper and lower mandible. However, it is necessary to pay attention to the fact that in easternmost populations of the nominate race fabalis high percentages of birds with an overall dark pattern on the colouring of the bill frequently occur. Although such birds are showing some resemblance with johanseni, their size and shape of the body as well as the structure of the bill are more or less equal with those of the nominate fabalis, whilst many of them are showing characteristic white plumages bordering the basal part of the bill especially along the cheeks and forehead, sometimes even at the chin. In former times Anser fabalis johanseni was a rare and scarcely observed vagrant to Western Europe, but the species has now become a regular winter visitor to the Netherlands and Germany during the last years of the 20th century. It is found in scattered families as well as in flocks of some tens or even hundreds of birds, merely in the eastern and southern parts of the Netherlands. Some evidence is found that there could be a relation between the recent appearance of increasing numbers of johanseni in Europe and the disappearance of these birds in the former wintering regions in Asia Minor or maybe even in Eastern Asia.
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