Geografische variatie bij ganzen Deel 5 De Oost-Siberische Toendrarietgans Anser serrirostris serrirostris

In the arctic tundra-zone of Eurasia two subspecies of the race Anser serrirostris are found, namely A. s. serrirostris in the east and A. s. rossicus in the west. The watershed between these populations should be located somewhere in the eastern part of the western half of the Taimyr-peninsula, where both types are slightly integrading into each other. According to recent field observations (Mooij & Litvin pers. comm.) the nominate race serrirostris is breeding from central Taimyr to the east of the peninsula (and further on to Anadyr and Kamchatka). The nominate race serrirostris differs from the western race rossicus not only by a larger size of the body and a heavier bill (but there is some overlap in this characters as a result of geographical integrading), but especially by a much paler colour of the overall plumage of these birds. So, seen from a distance without binoculars, a flock of typical serrirostris can be easily confused with Grey-lags or even Pinkfooted Geese! Moreover, also the head-bill profile, the position of the bill while the bird is watching and looking around (straight in serrirostris, somewhat erected in rossicus), and the diffuse structure of the flocks while feeding, are different from those found in the typical rossicus-race. The total population-size of serrirostris was estimated by Fox (1996) as to be less than 50.000 and declining, but according to recent information the actual size of the entire population should be very likely in an order of 100.000 – 150.000 birds. Although it was believed that all birds of the nominate serrirostris should be wintering in Asia, it has become clear that at least a part of the westernmost population is wintering in Europe and reaching the Netherlands with increasing numbers since the 1995-’96- season. The present stock of these birds wintering in The Netherlands can be estimated as at least 10.000 – 15.000 individuals. In autumn 2002 serrirostris arrived already in the latter part of September, while flocks of several hundreds up to some thousands of these birds were staying until the end of March during spring 2001, 2002 and 2003. This means, that serrirostris can be seen during a six-months period in The Netherlands, while on the other hand rossicus merely arrives after mid-October and mainly is leaving the country in the course of February.