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.”
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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Watch
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.
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