News release/sun compass

[Monarch Watch]

Monarch Butterflies Use a Sun Compass

	One of the great monarch mysteries is how do inexperienced monarchs
from Colorado to New England and the Canadian provinces all find the same
traditional roosts in Mexico each year? What environmental information is
used by monarchs to guide their migratory flights? Do they use the sun as a
compass, are they guided by the earth's magnetic field, do they follow
structural features of the landscape such as rivers and mountains, or do
they use a combination of these, or perhaps some undiscovered method?  To
begin to find the answer to this question, we conducted an experiment last
fall in which we  determined that the position of the sun is one cue that
monarchs use to navigate.
	Many animals are able to use the sun to orient their migratory
movements, but their interpretation of the sun's position depends on their
knowledge of the time of day.  In other words, if an animal's internal
clock says that it is morning, it will interpret the position of the sun to
be in the east, regardless of the sun's actual position.  Experimenters
have demonstrated sun compass use by controlling the timing of lights to
shift the internal clocks of subjects.    This change in internal clocks
causes the animals to misinterpret the position of the sun and change their
direction of movement in a predictable way.
	To determine whether monarchs use a sun compass to orient their
migratory flight, we collected migrating monarchs during September 1996 and
maintained them in the laboratory for 9-15 days under a light-dark cycle
six hours later than natural lighting conditions.  We then released
monarchs individually in an open field and watched each monarch for 1-5
minutes, running behind to estimate its body orientation.  Clock-shifted
monarchs were compared to monarchs which were held in the lab but not
time-shifted, and to naturally migrating monarchs.
	Both of the control groups flew in the predicted SSW direction.
However, the clock-shifted butterflies flew toward the WNW.  Even though it
was 3:00pm, the clock-shifted butterflies "thought" it was 9:00am, and flew
in a direction to the west of the sun's position.   This study demonstrates
that monarch butterflies in North America use sun compass orientation
during their fall migration,  identifying for the first time a major
orientation mechanism for monarchs.  That monarchs can still manage to
orient toward the SSW on overcast days suggests that they also have
alternative ways of orienting in the correct direction.

The citation for this study is: Perez, S., O. R. Taylor and R. Jander.
1997. Monarch butterflies use a sun compass. Nature 1 May, p 29



Monarch Watch
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