This presumed hybrid Eurasian Wigeon / Pfeifente (Anas penelope) x Mallard / Stockente (Anas platyrhynchos) has been wintering in Vienna since at least 2012 (there seem to be no sightings from summer, which points to but doesn’t necessarily mean that the bird isn’t there). J. Lehmhus brought up that it might be an intersex bird. And indeed, when I saw this bird for the first time, in January 2021, it should have been in full breeding plumage. But the bird showed „female-like“, brown feathers, i.e. on mantle and flanks and much less clearly marked plumage patterns than typical hybrids of this combination. Also the greyish-pink bill color seems odd. The term „intersex“ – usually refers to female birds that develop male plumage. This is commonly seen in Mallards, but less often detected in other species. In hybrids, intersex are suspected to be more common.