Mandarin Aix galericulata
As this species declines in its native range, the introduced population in the UK thrives and now accounts for a significant proportion of the world wide population. An extremely popular bird in captivity and escaped individuals may be encountered almost anywhere.
In Norfolk Felbrigg Lake is probably the most reliable site for feral birds. The female below is from there but while some of the others may possibly have originated from a feral population most were tame individuals that are probably more likely to be direct escapes from captivity.
The following birds are still in captivity.
Whilst leucistic birds are fairly unlikely to be encountered among birds that are bred in the wild, they are quite frequent in captivity, as the following examples illustrate:

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