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.

Sir John Mandeville [14th century CE] (Travels, chapter 29): I told them of as great a marvel to them, that is amongst us, and that was of the Bernakes. For I told them that in our country were trees that bear a fruit that become birds flying, and those that fell in the water live, and they that fall on the earth die anon, and they be right good to man's meat. And hereof had they as great marvel, that some of them trowed it were an impossible thing to be. ( Macmillan edition of 1900)

