Taverner's Cackling Goose Branta hutchinsii taverneri

This form turns up in the wild in the UK occasionally but I haven't yet had sufficiently good views of a wild one to get decent photographs. Instead here are some from a private wildfowl collection and it was their keeper (a keen birder) who informed me of their identity. One or two of them were surprisingly grey, which I thought might suggest hyrbidsiation with Barnacle Geese, however their owner didn't think so and indeed some photos of this taxon taken in the wild appear greyer than other Cackling Geese.

captive Taverner's Cackling Geese, private collection in Wereham (Norfolk, UK), 5th May 2017