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Overwinterende ganzen in de Ijzervallei: aantallen, verspreiding en trends
Devos, K. (2005). Overwinterende ganzen in de Ijzervallei: aantallen, verspreiding en trends. Natuur.Oriolus 71(Bijlage): 43-54
In: Natuur.Oriolus. Natuurpunt Antwerpen Noord: Turnhout. ISSN 1379-8863, more

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  • Devos, K. (2005). Overwinterende ganzen in de Ijzervallei: aantallen, verspreiding en trends, in: Devos, K. et al. (Ed.) Ganzen. Natuur.Oriolus, 71(Bijlage): pp. 43-54, more

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Abstract
    The valley of the river Yzer has only recently evolved into a traditional wintering area for geese. There were reports of important numbers of geese in the period of WWII but more concrete information about this is absent. In the second half of the 20th century initially hardly any geese were noted, but this changed in the hard winter of 1978/79. Then up to 60.000 geese were counted in the region, of which the largest proportion was in the Yzer valley upstream towards Diksmuide. In the 80s the numbers of geese in the Yzer area varied a lot, with quite large numbers in periods of hard frost and almost total absence in mild winters. This irregular pattern changed during the 90s. The Blankaart area of Woumen-Merkem developed gradually into a regular wintering area for geese. After a rapid increase in the second half of the 90s, the total number of geese has stabilised at about 10.000-11.000 individuals. White-fronted Geese Anser albifrons make up the main part of the goose population, with an average maximum of about 10.000 individuals in recent years. During the last 15 years the arrival of this species has become earlier and the winter peak has shifted from February to January. The Pinkfooted Goose Anser brachyrhyncus has become an annual visitor, but larger groups (> 100 individuals) are observed seldom and usually only for a short time. An expansion of the present distribution area from the Oostkustpolders (East coast polders) in the direction of the Yzer valley has not occurred. Tundra Bean Geese Anser fabalis rossicus are present during a large part of the winter, but only in low numbers which seldom exceed 100 individuals. For Greylag Geese Anser anser feral birds have developed into fast-growing local populations in the Blankaart area (max 432 individuals) and later also at Stuivekenskerke (max 227 individuals). Wild individuals, stopping over mainly in the spring, are met with very variable numbers from year to year (max 727 individuals). Barnacle Geese Branta leucopsis are present as only a few tens of individuals, if we ignore the late frost influx of February 1996 (max 456 individuals). As the numbers increased, the area used by the geese grew (in the form of a cyclical foraging pattern). Originally the expansion was restricted to different complexes within the Yzer valley at Diksmuide-Woumen-Merkem-Noordschote, but since the winter of 2002/03 larger groups are regularly seen in the polders around Stuivekenskerke. Other polder complexes (Lampernisse, Waleweiden Schorre, ...) only sporadically support small groups of wild geese, mainly in hard winters. The geese display a noticeable roosting movement towards the Blankaart lake at Woumen.Neckband data demonstrate a clear exchange of White-fronted Geese between the Yzer valley and the Oostkustpolders, but this is true for only a proportion of the birds. A direct arrival from other foreign goose areas is not unusual.

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