"It is a mystery," says monarch scientist Dr. Bill Calvert.

Here are some of the factors he considered when thinking about the question:

• Milkweed does grows in the Bahamas, so it's possible that some islands have a monarch population of their own.
• Some observers have reported monarchs appearing for a few weeks in the fall, and then disappearing until the next fall.
• One monarch that was tagged in New Jersey was recovered in the Bahamas. (One monarch tagged in Ontario was recovered in Cuba, too.)
• In the case of these 200 monarchs, it seems likely they were blown in.
• What was the weather like leading up to this observation? Is the timing correct?

Image: Tim Higgs

You're invited!
Travel to the monarch's winter home in Mexico this winter with Bill Calvert and Bonnie Chase.