Common pochard – Aythya ferina
is a medium-sized diving duck. The scientific name is derived from Greek aithuia an unidentified seabird mentioned by authors including Hesychius and Aristotle, and Latin ferina, “wild game”, from ferus, “wild”. The adult male has a long dark bill with a grey band, a red head and neck, a black breast, red eyes and a grey back. The adult female has a brown head and body and a narrower grey bill-band. The triangular head shape is distinctive. Pochards are superficially similar to the closely related North American redhead and canvasback.  Females give hoarse growls. Males have whistles cut off by a final nasal note aaoo-oo-haa.
These are gregarious birds, forming large flocks in winter, often mixed with other diving ducks such as the tufted duck, with which they are known to hybridise.

These birds feed mainly by diving or dabbling. They eat aquatic plants with some molluscs, aquatic insects and small fish. They often feed at night, and will up-end for food as well as the more characteristic diving.

In number of countries the population of Common Pochard is decreasing mainly due to urbanization of the natural habitats and their transformation, as well as due to overhunting. The pochard is one of the species to which the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA) applies.

It sounds like this
Recording by Peter Boesman from Xeno canto