Seasonal
History of a Monarch Butterfly Colony
Contributed by Dr. Bill Calvert
When the butterflies first arrive at a sanctuary in November, they are
strung out over miles of mountain ridges. Next they begin to gather into
clusters. Initially, the multiple clusters are not always connected. But
as the temperatures drop in late November and December, the butterflies
usually converge into 1 or 2 clusters (though there can be 3, 4, 5 or
even more groups).
Within each
cluster, there is generally an area covered with tightly-packed butterflies.
One gets the distinct impression that there are boundaries, even though
there might be holes in the area covered, and some butterflies on the
edges of the groups. A large cluster might cover 1,000--or even 2,000--
trees. But about 250 trees is more common.
By mid-December
the butterflies are packed into very, very dense clusters. At this time
there are as many groups as there will be for that year in that particular
sanctuary.
In December/January,
when the temperatures are the coldest, the butterflies are packed most
tightly on the trees. As many as 15,000 butterflies can be on a single
branch--so many that the branch actually bends under their weight!
After mid-February
these clusters begin to break up, or "bud." The colonies spread
out and gain area. They start to split up as the monarchs spread down
the canyons for nectar and water. When the butterflies come back up the
mountain they don't form thick colonies any more.
Journaling
Question
- If the
typical monarch weighs 500 mg, how much would a branch loaded with 15,000
butterflies weigh? (Give your answer in kilograms and in pounds. Also
name another object that weighs the same amount, for comparison.)
Try
This! How Many Paper Clips Bend a Branch?
- A monarch
butterfly weighs a little less than a paper clip. How many paper clips
can you string together to make a tree branch bend? Try it and let us
know!
National
Science Education Standards
- The behavior
of individual organisms is influenced by internal cues (such as hunger)
and by external cues (such as a change in the environment).
- All organisms
must be able to obtain and use resources, grow, reproduce, and maintain
stable internal conditions in a constantly changing external environment.
- Behavior
is one kind of response an organism can make to an internal or environmental
stimulus.
National
Math Standards
- Understand
meanings of operations and how they relate to one another.
- Compute
fluently and make reasonable estimates.
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