Voortgaande uitbreiding van Canadese Ganzen Branta canadensis over Drenthe

During 1989-95, only a single breeding site of Canada Geese was known in the province of Drenlhe during 1989-95, with resp. 1, 3, 3, 8, 12, 12 and 11 breeding pairs. This situation drastically changed in 1996, with only 7 pairs (and some unpaired individuals) at the main site De Mussels, single breeding pairs at six other sites and 3 breeding pairs at an eighth site. The main breeding site (De Mussels) is situated on an island in a sandpit, six other pairs bred on islands in fens and single pairs bred along a ditch and along a canal. Apparently, the increase in number of breeding sites had been partly caused by dispersion from the main breeding site, probably following deliberate disturbance by humans. Most ’new’ pairs bred within 10 km of the main breeding site, i.e. 1.8, 1.8, 2, 2.2, 2.8, 5, 6, 30 and 35 km. At least 8 out these 16 pairs produced goslings (but not neccessarily till fledging), with known brood sizes of 2, 2, 3, 3, 5 and 5 goslings (up to 3 weeks old). Breeding in fens, although safe from predators, may not be the best strategy of raising young because local food shortage necessitated long walks towards better feeding areas, resulting in increased exposure towards predators.