| 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.
 |
Our
fall monarch migration maps do not show a precise wave of
migration. Rather, it reflects the reality of overlapping |
Here
are some challenges:
- We
can't track the "first" monarch:
People see monarchs all summer in the northern U.S. states and
in Canada. This makes it impossible to tell when the first
monarchs leave and begin migration.
- We
can't
always tell if monarchs are migrating: Unless
people see large numbers of monarchs moving—or roosting—they
don't know for certain that the monarchs are migrating. (People
can watch for "directional flight" and be confident
that a single monarch is migrating.)
- 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 monarch migration
is not a clear, single wave — nor do the monarchs follow
a specific pathway. A person may see a spectacular migration one
day and not a single butterfly in the same place a day later.
Monarchs can travel high overhead and, with good weather, avoid
being seen.
- Can
you think of other challenges?
- Spring
migration is different: A clear wave of monarchs moves
up the map in the spring and 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. They 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.
|
| How
do we identify "Peak Migration"? |
- With
Difficulty! Sometimes it is only clear when the peak
occurred after the migration wanes. We often move sightings to
the "Peak Migration" map later in the season, when it
becomes easier to identify "peak." Our Peak
Migration map gives you the best snapshot of the wave of migrating
fall monarchs because we edit it so regularly. (You will be able
to identify peak migration in your area if you monitor the migration
on a regular basis.)
|
| Try
This! Map
"Migration Highlights" |
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