HEUNKS C., D. BEUKER, W. LENGKEEK, S. BOUMA, B. ACHTERKAMP & A.J. VAN DER WINDEN (2016) Scuba divers reveal secrets of Goldeneyes Bucephala clangula wintering in the Veluwerandmeren. LIMOSA 89 (2): 49-57.

In the winters of 2008/09, 2010/11, 2012/13 and 2013/14 Goldeneyes were counted and their foraging behaviour was studied at lakes Veluwemeer and Wolderwijd, the Netherlands (together referred to as the Veluwerandmeren). In addition, prey availability was studied at 10 observed Goldeneye foraging locations divided over the two lakes in the winter of 2008/09, by analysing bottom cores collected by scuba divers. Throughout each winter, complete counts of resident Goldeneyes were made from the shore using a telescope. Numbers varied from several hundreds to almost 2000 birds. Main aggregations were found in the shallow parts of the lakes; water depth at foraging locations was 0.5-3  m. The distribution closely matched the distribution of submerged aquatic plants. The composition of potential prey items was highly variable between sampling locations. The abundance of herbivorous food resources (root tubers of Chara spp. and Nitellopsis obtusa) and macrofauna (like Chironomidae and Amphipoda) was considerable at most locations. At some locations root tubers were the only potential food source available. Here, scuba divers noticed tracks of foraging Goldeneyes in the bottom, indicating that the birds actively dig for root tubers using their bills. Goldeneyes were frequently observed foraging close to Mute and Bewick’s Swans Cygnus olor and C. bewickii, which are known to make root tubers available to other waterbirds when foraging. Our results show that the foraging habitat of Goldeneyes in lakes Wolderwijd and Veluwemeer is dominated by Characeae and associated invertebrate fauna. Although no direct information was collected on diet composition, our results strongly indicate that nowadays Goldeneyes forage on a broad range of food types, including both animals and plants.

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