X Dark-bellied Brent
One of the interesting encounters at Holkham, Norfolk last weekend were Black Brant hybrids. A single bird (which was the most Black Brant-like) and a second bird, which was clearly a male, was paired to a female Dark-bellied Brent with single juvenile.
Both hybrids are known to be Black Brant X Dark-bellied Brent as they are returning birds which first appeared as juveniles in hybrid family parties (per James McCallum and Richard Millington).
Is this the first example of a back-cross, 2nd generation hybrid?
Couple photos for now. Thanks to James and Richard for much helpful insight.