This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Barnacle Geese (Medieval folklore)
The barnacle goose myth is a myth about the origin of the barnacle goose (Branta leucopsis) and brant (Branta bernicla) goose. One version of the myth is that these geese emerge fully formed from goose barnacles (Cirripedia). Other myths exist about how the barnacle goose breeds. The basis of all the myths is that the bird, Branta leucopsis, emerges and grows from matter other than bird eggs.
The most important way that the barnacle goose myth was propagated during the early Medieval period was through bestiaries. One such myth stated that Barnacle geese come from trees that grow over water. These trees produce birds that look like small geese; the young birds hang from their beaks from the trees. When the birds are mature enough, they fall from the trees; any that fall into the water float and are safe, but those that fall on land die.