The Mackinac Bridge is 5 miles long and connects Michigan's upper and lower peninsulas.

During fall migration, monarchs are often seen crossing the 24-mile bridge over Louisiana's Lake Pontchartrain. (You can see the city of New Orleans on the south shore of the lake.)

What can this single sighting tell you about a monarch's direction of travel, rate of travel, height of travel, and migration pathway?

We know the monarch was flying southward, because it was above the bridge that connects Michigan's upper and lower peninsulas. It was flying about as fast as people can walk, and it was able to fly ahead even faster. The bridge is over 500 feet high, so the monarch was flying at least that high.

Was the monarch actually crossing the bridge? It's possible! Based on other observations, we know monarchs avoid crossing open water; they fly along coastlines and often concentrate at the tips of peninsulas, hesitating to cross the water. When monarchs encounter a bridge at the end of a peninsula, they may follow that bridge just as they'd follow an extension of land. People have seen this in other places, notably the longest overwater bridge in the world, the 24-mile bridge that crosses Louisiana's Lake Pontchartrain. One observer there counted 142 monarchs crossing the bridge in 15 minutes.