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Ferruginous duck – Aythya nyroca

Ferruginous duck – Aythya nyroca
also ferruginous pochard, common white-eye or white-eyed pochard is a medium-sized diving duck from Eurasia. The scientific name is derived from Greek aithuia an unidentified seabird mentioned by authors including Hesychius and Aristotle, and nyrok, the Russian name for a duck.

The breeding male is a rich, dark chestnut on the head, breast and flanks with contrasting pure white undertail coverts. In flight the white belly and underwing patch are visible. The females are duller and browner than the males. The male has a yellow eye and the females have a dark eye.

These are gregarious birds, but less social than other Aythya species but where common it can form large flocks in winter, often mixed with other diving ducks, such as tufted ducks and common pochards. Forms pairs from January onwards and during courtship the male often curls his tail so that it dips into the water forming a triangular white patch of the undertail coverts. In areas where it is common it will form colonies at protected sites such as islands, often in association with gulls. Where scarce it nests singly, in dispersed and concealed sites.

It sounds like this
Recording by Stanislas Wroza from Xeno canto