Vanessa at night - migrations

Kenn Kaufman kennk at ix.netcom.com
Tue Feb 5 01:28:59 EST 2002


Eddie John wrote:

>This will be my last contribution on the subject,
>otherwise I can anticipate being asked whether
>a cruise ship from Israel docked in Cyprus at
>the same time! ...

I for one am grateful to Eddie John, Nick Greatorex-Davies, and others
for their detailed posts about observations of butterfly dispersal from
the Mediterranean region, the U.K., and northern Europe.  And I'm sorry
that those posts were met with badgering  from The Man Who Always
Contradicts People (old Python reference there).  Despite how it might
appear, many of us Yanks are actually sane and open-minded, and quite
interested in such relevant information.

The significant question here involves butterflies (such as Vanessa) in
strong dispersal mode that find themselves over open water at nightfall.
Do they keep going?  Some believe (well, okay, one person believes) that
they must fold up and drop into the drink within an hour after dark.
That's not impossible, given that some episodes of butterfly dispersal
are suicide flights for all practical purposes.  But in areas such as the
Mediterranean, where a crossing is feasible, there would be very obvious
selective advantages to continuing to fly.   Those that fold in the dark
and drown are certainly not going to pass along any genes, while those
that continue flying in the dark just might make it to another landfall
where they could breed.  It seems quite plausible to me that this kind of
selective pressure over a few thousand generations could enhance the
tendency of determined dispersers to keep flying when there's no safe
place to land.

Of course, this has nothing to do with a lack of butterflies cavorting
about the buddleias in the moonlight.  It also has nothing to do with V.
cardui migrating through the southwestern U.S. -- if they're flying over
land, it's no surprise if they stop for the night.  But it does have
significance for questions of biogeography.

Given that we're talking about an unusual set of natural circumstances
(strongly dispersing individuals in free flight over open water), I don't
see any way to approach this experimentally.  We can't just put
butterflies in a flight cage overnight and expect them to behave in the
same way.  Good old observation in the wild seems the only likely way to
make progress on the question.  Lepidopterists who are fortunate enough
to witness such an event would do well to document as many details as
possible and to publish those observations.  The geography of North
America is not well suited to such observation, as we don't have many
huge bodies of water at the right latitudes, so I'll continue to
appreciate such reports from our friends on the other side of the
Atlantic.

Kenn Kaufman
Tucson, AZ




 
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