Sources : Gull

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Birds 5.74): Larus is a bird, as the Glossa says, having a double nature. For in that place where unclean birds are prohibited by law [Israel?], this bird lives both in water and on land, and delights in both elements: swimming in the waters, flying in the air. - [Badke translation/paraphrase]

Bartholomaeus Anglicus [13th century CE] (Liber de proprietatibus rerum, Book12.23): The bird that is called Larus inhabiteth somtime in waters and somtime in the land. Therfore in Aurora it is written. Latus est fluminis habitator et incola terrae, / Nunc natat ut pisces, nunc volat inslar avis. That is to understand: Larus dwelleth both in rivers and lande, and swimmeth as a Fishe, and also flyeth as a Bird. - [Batman]