Monarch Migration Update: Sept. 16, 2010
Please Report
Your Sightings!

The spectacular migration of fall 2010 continues! The monarchs are giving a great show in the Great Lakes region, and have begun a clear advance down the Atlantic Coast. In the Midwest, the wind is holding the butterflies back, but get ready for that to change. Monarchs must avoid many hazards to survive their long migration to Mexico. This week, find out how two hazards—large bodies of water and storms—influence when and where monarchs travel.

This Week's Update Includes:

Image of the Week
Monarchs coming to roost at Owen Point, Lake Ontario
International Travelers
Finding safety at water's edge

News: A Great Show in the Great Lakes—and Beyond

It was Saturday morning in Michigan, just north of Detroit, when people looked skyward and saw them. A blizzard of butterflies was "floating overhead," "all around us," "at high and low levels over our house" and "everywhere we drove." The numbers were enormous and the sight was magnificent as monarchs poured out of Canada and into the United States.

All along the Great Lakes monarchs traveled last week. They were counted at rates up to 7,800 monarchs per hour. They gathered at night in roosts 15,000 butterflies big. Monarchs must avoid crossing large bodies of water unless the wind and weather are right. Observers in Mequon, Wisconsin saw how the wind and the Great Lakes affect the migration:

"We are on the western-most shore of Lake Michigan. When the wind is from the northwest, the monarchs funnel down along the shoreline to avoid being blown out over the lake."

Take a look at the roost map. It now shows a clear migration corridor for Canadian-born butterflies. This true story about a tagged butterfly also shows how monarchs travel to avoid crossing the Great Lakes.

The Atlantic Coast: Get ready to see the same migration pattern along coastlines in the east, where monarchs must avoid another great hazard, the Atlantic Ocean.

Right now, scientists are monitoring migration daily at the tip of the Cape May peninsula in New Jersey. At the time of writing, a spectacular migration was underway down the New Jersey coast.

"Long Beach Island, NJ, is currently seeing one of the most abundant showings of migrating monarchs in years -- if not decades. Light westerly winds have blown them over to this barrier island. There are far too many to even estimate a count. I have been rough counting them since the early 1970s and have to harken back to those early years to recall seeing so many."

Central United States: Roosts are stacked up in a line across Iowa where they have been stuck for over a week. Persistent south winds south of Iowa seem to be keeping them there. Keep your eye on the roost map and the wind forecast maps. When do you predict they'll fly? Get ready for the show!

Our southernmost roost was spotted in downtown Omaha, Nebraska, yesterday morning:

"There are hundreds and hundreds in my trees and my neighbors trees. It is amazing. I'm close to downtown Omaha and never would I think I would see this many here..... WOW!"

Monarchs migrating along Lake Erie shoreline

Video Clip
Monarchs migrating along Lake Erie shore.
Video: Joe Stephenson

Tagged monarch found! What do its travels tell you?

Tagged monarch reveals a migration pathway. More...

Graph: Number of roosts reported as of September 14th each year

Number of Roosts

Will the high number of roosts this fall mean a large population in Mexico this winter?


The Migration: Maps and Journal Page 
Map of All Monarch Butterfly Sightings: Fall 2010 Map of Monarch Butterfly Roosts: Fall 2010 Migration Journal Page

ALL Monarch


Fall Roosts


For Your Journal
This Week's Map Questions

Seeing Monarchs? Please let us know!

  • Report frequently—at least once a week—as long as monarchs are present.
  • Count monarchs: Tell us how many monarchs you see per hour (or minute).
  • To report your sightings, press here.
Research Question: How do monarchs respond to hurricanes and other storms?

Monarch scientist Dr. Bill Calvert was in Maine last week when Hurricane Earl approached the coast. How did the monarch caterpillars respond? How do butterflies stay safe when a storm strikes?


Bill Calvert and Bonnie Chase: Trip leaders to Mexico's monarch butterfly sanctuary region

The Next Monarch Migration Update Will Be Posted on September 23, 2010.