More About Our Fall Migration Maps Why Tracking Fall Migration is Tricky It is easy to spot monarchs in the fall, but it can be hard to tell if they are actually migrating. Tip: Roost Map Shows Clearest Migration Pattern Our map of overnight roosts shows the pattern of fall migration most clearly. Roosts are large concentrations of monarchs so they show where migration is strongest. Here are some challenges we have in tracking fall migration: We can't always tell if monarchs are migrating: People don't know for certain that the monarchs they see are migrating unless they see large numbers of monarchs moving, roosting, or flying in clear "directional flight." We can't track the "first" migrating monarchs. It's impossible to tell when the first monarchs leave and begin to migrate. This is because people can see monarchs all summer in the northern U.S. states and Canada and can't determine when the first monarchs leave to begin migration. We can't track the "last" monarch: People would not know immediately that they were seeing the "last" monarch, so we can't track the last monarch easily either. (What's more, late monarchs may be too late to migrate to Mexico due to cold temperatures. Thus, such a map would have little meaning as a migration map.) We can't tell the origin of "first" monarchs in southern states. In many southern states, monarchs are not usually seen during June and July. They re-appear in August. Where did they come from? Are they early migrants moving down from the north? Or are they the offspring of a small, local population whose numbers are building with each new generation? It's imposible to know. The nature of fall monarch migration: The migration does not occur at a predictable time along a specific pathway; all monarchs don't travel together in a clear, single wave. Monarchs can travel high overhead during good migration weather and avoid being seen at all, even during peak migration.A person may see a spectacular migration one day but not a single monarch the next day in the very same place! Spring migration is different: A clear wave of monarchs moves up the map in the spring because we map sightings of the first monarchs seen. This wave represents the "leading edge" of the spring monarch migration. Don't Hesitate to Report: All Monarch Sightings Are Important! Because of these challenges, we collect migration sightings in three categories, then make sense of the patterns. The categories are: "migration sightings," "overnight roosts," and "peak migration." Don't be concerned about selecting the right category when you report your sightings. We review all sightings carefully and can edit categories, if needed. Try This! Map "Migration Highlights" Because it is difficult to map a clear wave of fall migration, we recommend that you create a map of migration highlights. See: Highlights Along the Migration Trail.

Copyright 1997-2011 Journey North. All Rights Reserved. Questions or comments? Contact us.