The Overnight Roost
August 31, 2017 by Elizabeth Howard
  Overnight roosts are a traditional sign of fall migration. What can we learn by studying them?  
Monarch Butterfly

"There are many species of trees in this park so it's interesting how they choose only oak. I love when they flash for another butterfly to join the cluster," reported Darlene Burgess from Leamington, Ontario on August 28th.

Beginning to Build
Excitement was in the air this week as observers witnessed clear signs of migration. People were reporting monarchs flying by day, stopping to refuel, and roosting for the night.

"Hundreds of monarchs were flying over our house from 7 to 7:30 this evening. The first ones were flying strongly south. By about 7:40 pm, they were looking for a place to spend the night," reported Sandi MacKellar from Callander, Ontario on August 28th.

Tracking Overnight Roosts
As you look at the map, notice where roosting began this week. All sites are in southern Canada and northern U.S. states. Monarchs must get out of the north while nectar is still available and before cold temperatures trap them. Migration begins early in the north; it's only August.

Roosts Reveal Pace and Pathways
Week by week, roosts show us where large concentrations of monarchs are. Get ready to watch the map reveal the main migration pathways to Mexico and the pace of the migration.

Roosts Raise Questions
Scientists have many questions about fall roosting behavior.

  • Monarchs migrate alone; why do they gather at night?
  • How do they find one another?
  • What can we learn by studying overnight roosts?
Monarch Butterfly
Roosting Behavior
Tami Booth

Map of All Monarch SightingsMap of Overnight Roosts
Tracking Roosts

Monarch Butterfly
Roosting on a Rush
John Jonas

Why Form Overnight Roosts?
Why do Monarch Butterflies Form Overnight Roosts During Fall Migration? Why do Monarch Butterflies Form Overnight Roosts During Fall Migration? Why do Monarch Butterflies Form Overnight Roosts During Fall Migration?


Report Your Sightings
Report all monarchs you see — adults, eggs, larvae.
What to Report to Track Fall Migration Monarch Butterfly: Adult Sighted Monarch Butterfly: Egg or Larva Sighted
What to Report Adult Butterflies
map | list | animation
Eggs and Larvae
map | list
Monarch Butterfly Migration Map: Fall Roosts, Fall 2017 Monarch Butterfly Migration Map: Peak Migration Fall 2017 Journal
Fall Roosts
map | list | archives | animation
Peak Migration
map | list | animation


Next Update September 7, 2017