Back to this week's update. 

How many made it to Mexico?
Two months ago these monarchs were resting at a roost in Ontario, Canada. They had 2,000 miles left to fly to reach their winter home in Mexico. How many survived the trip? We'll never know! However, this week you will learn how scientists estimate the number of monarchs that make it to Mexico each year.

Monarch butterflies roosting during fall migration.

Image courtesy of David Bree