Mallard x Common Eider hybrid, Korshage, Rørvig (Zealand, Denmark), 9th January 2011 - copyright Klaus Bjerre
(photo ID: 2591)
This is a distinctive hybrid that has occurred several times in the wild, perhaps surprisingly given the distance in their relationship.
What may be the same bird is shown below, photographed the following winter.
Mallard x Common Eider hybrid, Gniben, Sjællands Odde (Zealand, Denmark), 11th February 2012 - copyright Jakob Engelhard
(photo IDs: 2592-2593)
A photograph showing this bird standing (thus giving a view of its belly and legs, but also of its speculum) appears here.
Mallard Anas platyrhynchos
Common Eider Somateria mollissima