About Our Fall Migration Maps
Tracking Fall Migration is Tricky
is easy to spot monarchs in the fall, but it can be hard to tell if
they are actually migrating.
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.
are some challenges we have in tracking fall migration:
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."
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.
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.)
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.
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!
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.
Hesitate to Report: All Monarch Sightings Are Important!
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.