Tracking Begins

August 24, 2017 by Elizabeth Howard

Sightings of southbound butterflies, intense nectaring, and the first overnight roosts are being reported. Share your observations and help tell the dramatic story of the monarch's journey to Mexico.

Image by Anna-Lise Scheel of Halton Hills, Ontario

Fall Migration is Underway

Observers across the northern range have reported signs of a productive breeding season. Get ready for an eventful fall migration!

Monarchs Are…

Monarchs are changing dramatically at this time of year, in physiology and in behavior. They are:

1. Becoming Migratory

Watch for signs of migratory monarchs:

  • flying in directional flight
  • clustering in overnight roosts
  • nectaring intensely

2. Responding to Daylength

Declining day length is a central cue that triggers the monarch’s migratory state. In the northern breeding range, photoperiod is falling by 20 minutes this week. This sends a signal that it’s time to go to Mexico.

3. Emerging in Diapause

Beginning in mid-August in the north, adults are in diapause when they emerge from the chrysalis. They are full grown — but not reproductively mature. Their reproductive development is on pause. These monarchs will not complete development and begin to mate until next spring in Mexico.

4. Beginning a Long Life

The same hormone deficiency that leads to diapause also leads to increased longevity. Breeding monarchs live only 2-6 weeks; migratory monarchs live up to 8 months.

5. Accumulating Fat

Monarchs are shifting focus now from breeding to intense feeding. They must build body fat to fuel migration and to survive the winter in Mexico.

Journal: The Magic of Migration