assessing cloud cover and wind

[Mark Walker]

Corina Brdar asked:


> Hello all,
> 
> I was wondering if anyone knows of any methods used to assess wind and
> cloud
> cover at a scale that is meaningful for butterflies.  I'm doing research,
> and it involves observing butterfly behaviour, and I need to evaluate
> these
> things since they have such marked affects on their behaviour.
> 
> 
	I'm not quite sure I understand what you are asking for, but in
general I would say that it really depends on the species, the location, the
time of year, and the short term history of local weather patterns.

	While most butterflies will "hide" on days of limited sunshine,
there are certainly many exceptions to this.  For example, while visiting
southern Texas last year, I was amazed to find an incredible number of
butterflies on the wing while under a completely overcast sky.  The
temperature was over 85 degrees, however, so there was obviously sufficient
kinetic energy.  Other examples might include individuals who have been
delayed from emerging the pupal stage on account of a delayed spring.  I
have seen butterflies in this category make use of every 5 minute blast of
sunshine they can get from behind an otherwise clouded sky.  An example
includes an early summer visit to at-timberline elevations in the eastern
Rocky mountains - where thunderheads dominate the early afternoon sky, but
the butterflies can be seen flying down from their treetop perches to nectar
during very short breaks in the weather.  Pieris napi don't concern
themselves much with extent of sunshine, and can often be found flying under
even the most thorough of tree canopies.  Sap loving butterflies are in this
category, also, often preferring shade to open sunshine.  Many desert
butterflies, meanwhile, prefer to fly in patchy weather - especially when
this immediately follows a rainstorm.  

	On a slightly different note, butterflies can be found on days that
they are not actively flying.  There were excellent field reports last year
from Massachusetts on Callophrys species that were effectively spotted and
counted during rainy, overcast skies by searching for their resting places
(now this is dedication).

	In general, however, I would say that I base my likelihood of
pursuing leps on a combination of both extent of sunshine and temperature
(although temperature is certainly not a globally definitive indicator).  On
days forecasted with 100% rain over an extended period of time, I will stay
home (or be content with walking in a butterflyless rain).  On days of
partial but mostly cloudy skys, I might only venture out if I know that
there are other reasons to expect activity (as per above).  When it's March,
and I've been going through winter butterfly withdrawal, almost any day with
a chance of patchy sunshine will be enough to get me out of the house.

	Hope this helps,

	Mark Walker
	Mission Viejo, CA  USA