VOSKAMP P & DRIESSEN J (2003) Common Goldeneye Bucephala clangula as a breeding bird in the Netherlands: population development and habitat use. LIMOSA 76 (2): 59-68.

The Common Goldeneye has established a small breeding population in the Netherlands from 1984 onwards. We consider this settlement as a natural one, since it is in line with the expansion of the species' breeding range in Western Europe. The first breeding attempts were recorded in the valley of the river IJssel, a branch of the river Rhine. Outside this area only a few breeding pairs were found (Fig. 2). In the IJssel area the population grew to a maximum of 14 pairs in 1992. After 1992 the population stabilised around eight pairs, with an increase to 11 pairs in 1999, caused by an expansion to the north of the IJssel area. Breeding results were low during peak years, but stabilised at approximately 65% successful pairs (Fig. 1). Ponds and small lakes close to the river, preferably bordered by old trees or deciduous forest, form the breeding habitat. Nest sites can be quite far from the water, in this study up to 2.5 km. Unlike other new settlements of this species this population did not strongly depend on nest boxes (Table 1). Most breeding attempts were recorded in natural tree cavities and cavities in pollard trees, that are common in the traditional riverine landscape of the Netherlands. Goldeneyes were faithful to breeding sites, especially to those with good results in the previous breeding seasons: 17 out of 27 nests were used for more than one year (Fig. 3). Eighteen out of 24 breeding sites were outside the area that is regularly flooded by the river, but most females raised their young in wetlands situated close to the river. This means that females had to guide their young across a dike, which is in most cases a busy motorway. Ducklings that were not led to the river floodplain had a significantly lower daily survival rate (Fig. 4). This could be the reason why females undertake these potentially dangerous and long (up to 3.4 km) journeys with their young. Possibly the ponds and lakes outside the river area are good feeding habitat for adult Goldeneyes, with little underwater vegetation. Ducklings however, suffer high predation risk in these waters and have difficulties seeking cover from the aggression of territorial Coots Fulica atra. It is unknown why the Goldeneye breeding population has not yet expanded into other areas of the Netherlands that seem suitable for the species. Competition with Mandarin duck Aix galericulata, which has similar nest site preferences, is discussed as a possible explanation.

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