Why Migrate on a Bridge? The longest bridge in the world is pictured below (see arrow). It is 24 miles long. The bridge crosses Lake Pontchartrain in Louisiana. People drive south on the bridge into the city of New Orleans. It takes a car about a half hour to drive across the lake. Monarchs are often seen migrating on this bridge in the fall, right beside the cars. Why do you think they do this? Think....then read on >> Image: NASA Earth Observatory Can you see the bridge, the tiny cars crossing it, and the city of New Orleans? Click on the image! Copyright 2006 Journey North. All Rights Reserved. Please send all questions, comments, and suggestions to our feedback form.