DIJK K VAN (1998) Moulting Black Swans Cygnus atratus at Lake IJsselmeer, The Netherlands. LIMOSA 71 (2): 78-80.

Lake IJsselmeer is a shallow freshwater lake of 2000 km2 with large summer concentrations of moulting nonbreeding Mute Swans Cygnus alar. Since at least 1978, non-breeding Black Swans are also present during summer. Five Black Swans that were caught on July 25, 1983, showed slight biometric differences between males and females (Tab. 1). They had started wingmoult between the end of June and the second half of July. On Lake IJsselmeer most birds are seen in mid-summer (Fig. 1,2), at the peak in the number of moulting Mute Swans. With a maximum of 5-10 in the mid-eighties, Lake IJsselmeer held the most important moulting concentration in The Netherlands (only c. five breeding pairs at the time). Around the mid-nineties, numbers had increased to a maximum of 20. Due to a recent strong increase, the Delta-area is nowadays the most important site for moulting non-breeders.

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