Black Brant Branta (bernicla) orientalis (formerly nigricans)
Brent Geese belonging to the North American and east Siberian form orientalis now regularly occur in Norfolk - several individuals are recorded most winters. Note that the old scientific name nigricans is now applied to Grey-bellied Brant, formally described for the first time in 2013, leaving Black Brant with a new name, orientalis.
Many of the Black Brants that winter in western Europe have produced hybrids with Dark-bellied Brent Geese, and this makes their identification far more difficult. Some hybrids can be reasonably easy, but others may be much more like either parent species - and to complicate matters further backcrossed hybrids occur as well.
Over the years I have identified a number of Black Brant-like birds as hybrids on account of the back and belly not being dark enough. Whilst this was undoubtedly valid in some cases I had not always appreciated the extent to which these parts can vary in appearance according to light, and it may well be that I have misidentified some perfectly good Black Brants as hybrids. Under certain light conditions the black on a Black Brant's back and breast can be so dark that it doesn't contrast at all with the black neck, but on the same bird in different lights (including bright sunshine) these parts can contrast quite strongly with the neck (although they should always appear darker than on Dark-bellied Brent Geese in the same conditions).
The extent of dark feathering within the white flank patch is certainly variable with all forms of Brent Goose and the precise extent of the white neck collar is also variable. In both cases there may be little overlap with pure Dark-bellied Brent Goose but I have come to believe that a slightly less prominent white flank patch than on the most obvious birds, or a white neck collar that doesn't reach quite so far round the back of the neck as it does on some birds, are not probably not good evidence of a hybrid identity.
In view of the above I have now lost confidence in the labelling of several birds I'd originally got down as hybrids, and although I still think some of them were hybrids (I'm sure a few were) I think several of them were more likely pure birds after all. I haven't yet developed a full understanding of the limits between pure and hybrid birds - more study and more learning is needed!
I have now moved photos of birds that I believe most likely to involve hybrids to a separate page Black Brant x Dark-bellied Brent Goose. That is not to say that I am 100% certain that every bird on this page is a pure Black Brant and if you believe any not to be then please do get in touch.