The Overnight Roost
Monarch butterflies only migrate during the day. At night, they come down to rest. They spend the night in trees, clustered together in “roosts” or “bivouacs.”
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In the morning, the butterflies must warm up before they can fly. To fly WELL they need to attain thoracic temperatures at least 55 F (13 C). (Monarchs cannot even crawl when their thoracic temperatures are below 41 F (5C).)
As this map shows, temperatures drop as the fall season progresses. Monarchs have a shorter and shorter window of time each day in which they can fly. This is one reason monarchs must leave the north before it gets too cold!
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how the temperatures fall in the fall! |
Try This! Too Cold to Fly Today?
- Record and graph the daily temperatures in your hometown this fall. When does the temperature drop below 55F?
- As the season continues, for how many hours in each 24 hour day is the temperature below 55F?
- Note that monarchs can bask in the sun and/or shiver to raise their temperatures above air temperature. Therefore, keep track of sunny and cloudy days to get a better sense of when monarchs could fly.
National Science Education Standards
- Weather changes from day to day and over the seasons.
- The behavior of individual organisms is influenced by internal cues (such as hunger) and by external cues (such as a change in the environment).
- Regulation of an organism's internal environment involves sensing the internal environment and changing physiological activities to keep conditions within range required to survive.
