Papillon du jour (butterflies) flying in the middle of the night.

[Martin Bailey]

Contrary to popular opinion the winds that you may feel at ground level do
not continue upward forever.  Often when you look up on a cloudy day you may
see two separate cloud formations going in opposite directions pushed by
contrary wind currents.  Similarly, the air does not necessarily get colder
as air rises to higher altitudes.  While it is not possible to see the
affects of air temperature become warmer at higher altitudes directly, that
is what is happening when you see what is known as a superior mirage.  And
in the case of a fata morgana ( a mirage where you see "castles floating in
the sky") you are witnessing one of the affects of air of varying density
and  temperatures stacked on top of one another.

So what does this have to do with migrating butterflies flying at night.  In
the case of wind direction very little.  Butterflies can just as easily tack
into the wind as fly with a following wind if they choose to.

Air temperature is a different matter.  Being cold bloodied, butterflies are
only active within prescribed temperature ranges.  Warm air currents do not
necessarily have to be at ground level where you and I are most likely to
see butterflies. Hence, there is no reason why if it is still warm enough
for butterflies to fly at higher attitudes on some nights than at ground
level that they will not do so.

I, therefore, propose two hypotheses:
Migrating butterflies will continue to fly at night over water if they are
physiologically capable of doing so.  To land is to drown.
Migrating butterflies will continue to fly at night over land if they are
physiologically capable of doing so until they find suitable habitat to
roost on.

Martin Bailey,

greetings from:  Weyburn, SK., Canada.
                         49.39N  103.51W


 
 ------------------------------------------------------------ 

   For subscription and related information about LEPS-L visit:

   http://www.peabody.yale.edu/other/lepsl