Greylag Goose x Barnacle Goose Anser anser x Branta leucopsis
There can be little doubt that one of the parents of this hybrid is Barnacle Goose but the other parent was less certain. Greylag Goose seems the most likely option as it accompanied Greylag Geese and nothing in its appearance gives reason to challenge this assumption.
In 2005 it appeared to be paired with a Greylag Goose and on a subsequent visit the two birds were looking after goslings. At first sight this would appear to indicate that the goslings were second-generation hybrids, backcrossed with Greylag Goose. As far as I know there is no proof yet that Anser x Branta hybrids can be fertile, so this would be a valuable thing to establish, but unfortunately they were not seen on subsequent visits. However the goslings appeared to resemble Greylag Goose goslings and it is probably more likely that the hybrid adult had simply adopted the Greylag Goose goslings.