Vanessa at night - migrations

James Kruse fnjjk1 at uaf.edu
Mon Feb 4 16:33:28 EST 2002


on 2/4/02 5:01 AM, Chuck Vaughn at aa6g at aa6g.org wrote:

> It seems to me the way to answer this question is for someone
> to get a pair of night vision googles and use them during a
> V. cardui migration. Certainly you'll be able to see a few
> of them flying by on a clear night, especially in the mid
> spring to early summer when the summer Milky Way is high in
> the sky and providing maximum light.

I have had the opportunity to use night vision goggles (in a different
context). Night vision goggles are designed for stationary observation of
human or vehicular activity. Although you can see "in the dark" very well,
even with passive IR, the depth perception is awful. You can trip and fall
and hurt yourself because you cannot discern up or down hills, etc. You
still literally stumble around in the dark. Also, as objects become closer
to your face, especially small ones, you cannot make them out very well. In
theory, you could do a "Butterflies Through Night Vision Binoculars", but it
would be an odd array of green blobs and not very useful. I think I could
tell the flight of a butterfly from the flight of most moths, but not what
species they were, except perhaps by behavior. You could easily set up an
observation post on a trail (in a boat?) where butterflies have been
streaming by all day, and record what time exactly the last ones go by, or
if they never stop.

I, for one, do not find the thought of butterflies flying in the dark over
water during migration particularly distasteful. I doubt the orientation is
very good, and may amount to random wanderings and a lot of mortality if the
night is very dark and there are no lights, stars, or unsuspecting boats. I
do think that they land if/when they can before pitch dark, and that flying
at night is not a "normal" activity of diurnal species. It might be
interesting to tag migratory species with some sort of tracking device and
monitor them day and night. Not like traditional monarch tagging (tag them
here, find them there stuff) but something more intensive. Bugged bugs....

I have tended light and bait lines for over 25 years. I have attracted
butterflies to lights, but never my flashlight. I think that most of the
butterflies that have come to my lights were either confused (bright merc
vapor lights) or were disturbed during my setting up. I have never seen
butterflies at my bait trees at night, but they often coat them during the
day. I have monitored the bait trees through the dusk period, and the
Vanessa spp. are replaced quickly by the first moths. Even if they can
migrate at night, I very highly doubt that they feed at night.

Just my anecdotal two cents.

Jim

James J. Kruse, Ph.D.
Curator of Entomology
University of Alaska Museum
907 Yukon Drive
Fairbanks, AK, USA 99775-6960
tel 907.474.5579
fax 907.474.1987
http://www.uaf.edu/museum/ento



 
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