Too Cold to Fly?
The Effects of Temperature on Fall Migration
(Slideshow Overview)

A Race Against Time
Monarchs must hurry during fall migration. The butterflies must leave their northern habitat before they get trapped by the cold!

Cold temperatures paralyze monarchs. A monarch can't fly unless its flight muscles are warm enough. When it was below 50 degrees, it took an hour for this butterfly to crawl a few feet.

Flight Threshold
A monarch's flight muscles must be 55°F (13°C) before the butterfly can fly

Monarchs are cold-blooded. This fact affects every moment of their lives. Cold-blooded animals do not maintain a warm body temperature. Their temperature depends upon the surrounding environment.

Warming Up
Cold-blooded monarchs have special behavioral adaptations for warming up. Monarchs can bask in the sun and they can shiver. Both adaptations help a monarch raise muscle temperatures to flight threshold.

Falling Temperatures
These maps show how quickly air temperatures drop as the fall season progresses. Watch what happens between August and December.
As temperatures fall, monarchs have a smaller and smaller window of time in which they can fly.

Warm Enough to Fly?
Air temperatures help us predict whether a monarch could warm its muscles to flight threshold. As a general rule, monarchs need air temperatures of at least 50°F on a sunny day (or 60°F on a cloudy day).

Temperature and Migration
Temperatures influence when, where, how fast, and how high monarchs can fly. As you follow fall migration, predict when and where a monarch could fly based on daily temperatures.