The OP provided in the link under context

Such fiction became science in the 1600s, according to Harrison, and greatly influenced Morton’s theory of the moon migration. But in 1676, a man named Francis Willughby set us down the path to avian truth when he published Ornithologia, a masterwork of bird science we can file with such classics as John James Audubon’s Birds of America. While Willughby, like Morton, refuted Aristotle’s notion that swallows hibernate, he wasn’t under the impression that they instead went to the moon. More modestly, it was to the warmth of northern Africa.

Though, it’s funny you mention the mud, given Aristotle’s belief that eels - which apparently lacked genitalia - just spontaneously generated from mud. Eels are weird, so I don’t fully blame him, but it’s so goddamn funny to think that they just spontaneously form into existence when it rains.