Vanessa at night - migrations

[Mark Walker]

While I don't personally doubt the possibility of Vanessa butterflies flying
throughout the night when otherwise compelled to do so (I don't think vision
is a prerequisite, btw, especially considering the crazed and
other-than-visually-driven behavior of migrating V. cardui), I must
substantiate Paul's other hypothesis that Monarch butterflies fly over the
Sierra Nevada.  As those who participated in the thread he's referring to
may recall, I actually have a record from the summit of Mt. Whitney from
1970.  The bug was flying above 14,000 ft., pretty intoxicated, but
nevertheless present at this most highest point in California (time of
capture was just after sunrise in the chilly August air).

On the other hand, I have never witnessed any "clouds" of Monarchs while
backpacking the more than 500 miles I've trekked over the years in the High
Sierra.  None of these weeklong trips were during the month of November,
however.  I know they are extremely common on the western flanks in
September.

Mark Walker.

> -----Original Message-----
> From: Paul Cherubini [mailto:monarch at saber.net]
> Sent: Tuesday, February 05, 2002 1:07 AM
> To: leps-l at lists.yale.edu
> Subject: Re: Vanessa at night - migrations
> 
> 
> > 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.
> 
> Yes, Ken some of us think Vanessa butterflies are likely 
> functionally incapable
> of oriented flight within an hour after sunset because they lack dark 
> adapted eyes - in plain english they are probably 
> functionally blind at night
> 
> Page 228  R.F. Chapman - The Insects, Structure and Function:
> (College textbook used for Courses in Insect Morphology & Physiology):
> 
> "The flight activity of many insects is limited by light intensity and
> Lewis and Taylor (1965) conclude that this is the major factor 
> controlling times of flight.  For instance many day-flying 
> insects, such
> as butterflies and Hymenoptera, are not active in the dark and
> aphids will not take off when the intensity falls below 20 
> ft.-candles."
> 
> Then the book goes on to describe and illustrate the structural
> differences between light adapted and dark adapted eyes
> http://www.mindspring.com/~cherubini/eyes.JPG
> 
> A few years ago on this forum the tables were turned and I was
> the one making a fantastic claim about insect flight capabilities.
> I reported that about a half dozen or so tagged monarchs released
> near Bishop, Calif (north of Mt. Whitney) during the first week 
> of November 1991 were recaptured along the south-central California
> coast just northwest of Los Angeles about 10-20 days later. I tried to
> claim this was good evidence the butterflies likely flew over 
> the frigid 
> 13,000 foot snow capped Sierra Nevada Mountains north of
> Mt. Whitney in early November.
> 
> Everyone else thought it was highly unlikely the monarchs flew
> such a fantastic direct route back to the California coast. 
> They thought
> the butterflies proably flew a less direct route down the Owens Valley
> and avoided crossing the Sierra Nevada Range.  I wasn't too
> thrilled, but accepted their challenge as constructive
> criticism.  In later years, I did another release further north near 
> Reno, Nevada during the first week of November and had
> one recaptured on the central California coast at Morro Bay
> within a week or two later.  This experiment more definitively
> suggested that some of the monarchs did indeed likely cross
> the central Sierra Nevada Mountain Range in early November. 
> 
> Paul Cherubini
> Placerville, Calif.
> 
>  
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