Cascading Behavior
The most spectacular behavior occurring late in February
and in March is "cascading." Literally tens of thousand of butterflies
suddenly push off their perches, en masse, and fall downwards. After a
fall of 3-5 meters they begin to fly, all in the same direction.
The phenomena is absolutely awesome. Butterflies fill
the sky at all levels for a period of up to several minutes. Gradually
they fly out of the area or land in nearby foliage--with only green spots
on the branches where the tens of thousands of butterflies had recently
been. Sometimes one cascade will trigger another, resulting in a sequential
cascading from numerous branches in the colony.
The cause and purpose of this spectacular behavior remains
a mystery.
There are times during the over-wintering period that bird predators can
trigger a cascade in a butterfly colony. But the phenomena we witness
in March is orders of magnitude greater than any cascading associated
with the presence of birds.
The local people believe it is the noise made by people
observing the butterflies that causes cascading. However, no one has shown
that monarchs can "hear" airborne sound waves. Monarchs do seem
to cascade in response to the presence of people, and this is of concern.
For the first time last week (Feb. 18, 2003), I noticed
that most of the cascading (but not all of it) occurred during cloudy
periods. In the past, I don’t recall having noted any correlation
with clouds or sun. But maybe that’s just because I never noticed
it before. I’ll certainly be paying attention from now on.
Nevertheless, the cause is still a mystery. We saw no
birds in the colony, and we humans were located far from the site of the
cascading. I don’t know, it must just be some sort of manifestation
of colony break up. It just can’t be related to anything else. And
why it occurs during cloudy weather, I just don’t know.
Journaling Questions
- Other than sound or sight, can you think of another
way the monarchs might be able to sense the presence of people?
- What experiment could you design to try to tease out
the cause of cascading?
National
Science Education Standards
Science as Inquiry
Ask a question about objects, organisms, events. (K-4)
Identify questions that can be answered through scientific
investigations. (5-8)
Science investigations involve asking and answering a
question and comparing that to what scientists already know about the
world. (K-4)
Scientists develop explanations using observations (evidence)
and what they already know about the world. Good explanations are based
on evidence from investigations. (K-4)
History
and Nature of Science
Although men and women using scientific inquiry have learned much about
the objects, events, and phenomena in nature, much more remains to be
understood. Science will never be finished. (K-4)
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