<p>I put fortuitous circumstances because since Wenner’s argument was that migration was NOT what the butterflies were doing (they were merely being blown away by wind by chance, not intent), some other factor was causing them to change location. Reiteration: they were CHANGING LOCATION, not MIGRATING. So, what caused their change of location? The southward wind, a fortuitous circumstance.<br>
“fortuitous: happening by accident or chance, rather by design”</p>