A bit info from Wikipedia:
The Barnacle Goose (Branta leucopsis) is a species from the genus of the so called "black geese". Their range is from the North parts of the Atlantic (Greenland, Svalbard, Novaya Zemlya) during the breeding season down to Netherlands during the wintering.
There were very strange legends about that bird, which was believed to be essentially the same creature as the barnacle. This gave rise to the English name of the barnacle goose and the scientific name of the brant. It is sometimes claimed that the word comes from a Celtic word for "limpet", but the sense-history seems to go in the opposite direction. The barnacle 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 legend persisted until the end of the 18th century. In County Kerry, until relatively recently, Catholics could eat this bird on a Friday because it counted as fish. In Judaism birds that grow on trees are not kosher.