This duck appears to be a hybrid between a Northern Shoveler and an Australasian Shoveler. He was in a group of Northern Shovelers.
He has the white face stripe of the Australasian Shoveler and a mottled brown body but (almost) the white chest of the Northern Shoveler.
Thanks to Joern Lehmhus, hybrid duck expert in Germany, for confirmation that this drake is, as suspected, a hybrid of Northern and Australasian Shoveler parents.
The hybrid drake was in a group of Northern Shovelers.
The "eclipse" plumage looks very similar to the Australasian Shoveler