Barnacle goose were of the same nature as other birds. The question of the nature of barnacle geese also came up as a matter of Jewish dietary law in the Halakha, and Rabbeinu Tam (1100–71) determined that they were kosher (even if born of trees) and should be slaughtered following the normal prescriptions for birds. The mythical barnacle tree, believed in the Middle Ages to have barnacles that opened to reveal geese, may have a similar origin to the other legends already mentioned. Barnacle goose The barnacle goose ("Branta leucopsis") belongs to the genus "Branta" of black geese, which contains species with
Greylag goose behaviour. Greylag goose The greylag goose ("Anser anser") is a species of large goose in the waterfowl family Anatidae and the type species of the genus "Anser". It has mottled and barred grey and white plumage and an orange beak and pink legs. A large bird, it measures between in length, with an average weight of . Its distribution is widespread, with birds from the north of its range in Europe and Asia migrating southwards to spend the winter in warmer places. It is the type species of the genus "Anser" and is the ancestor of the domestic goose, having