This video from the USA says about itself:
27 January 2016
A male Ruddy Duck in nonbreeding plumage dives for food and comes back up again. Ruddy Ducks forage mostly by diving to the bottom of shallow ponds, straining mouthfuls of mud through thin plates on their bills and swallowing the prey items that are left behind. They eat aquatic insects, crustaceans, zooplankton, and other invertebrates, along with small amounts of aquatic plants and seeds. At the end of the film, a Gadwall swims by. Video recorded by Jay McGowan in New York.