Brant (goose) the "Agreement on the Conservation of African-Eurasian Migratory Waterbirds" applies. "Branta" is a Latinised form of Old Norse "brandgás", "burnt (black) goose", and "bernicla" is the medieval Latin name for the barnacle. The brant and the similar barnacle goose were previously considered one species, formerly believed to be the same creature as the crustacean. That myth can be dated back to at least the 12th century. Gerald of Wales claimed to have seen these birds hanging down from pieces of timber, William Turner accepted the theory, and John Gerard claimed to have seen the birds emerging from their shells. The
Swan goose in collections, and escapes are not unusual amongst feral flocks of other "Anser" and "Branta" geese. The swan goose is large and long-necked for its genus, wild birds being long (the longest "Anser" goose) and weighing or more (the second-heaviest "Anser", after the greylag goose, "A. anser"). The sexes are similar, although the male is larger, with a proportionally longer bill and neck; in fact the largest females are barely as large as the smallest males. Typical measurements of the wing are in males, in females; the bill is about long in males and in females. The tarsus of males