Texas Grill Count

Mark Walker MWalker at gensym.com
Fri Sep 18 11:01:51 EDT 1998

Here's a blurb from an offline exchange with Kenelm I thought might be of

	Kenelm wrote:

		Now for a totally different subject. I read your posting on
	bile radiator butterfly counts with interest--but have some
questions. I
	have twice driven across the continent on collecting trips, and the
	of butterflies on the radiator was really quite small (although I do
	some figures for Tiger Swallowtail road kill in Alaska which show
that it
	can be quite high compared to any collecting I know of). Your
numbers are
	_huge_--and thus I have a question, as follows: Did you run into a
	of a single species? Or were these counts made up of many species?
	did you do the counting? That's a large number--I know because I
	the yellowjackets that were killed in a trap I ran some years ago
	1100) and got rather tired of counting! Obviously you didn't have
all those
	on the grill at any one time--you would have boiled over.  :-)

	I was hoping you would ask me about this.  I won't say that my
experiments were flawless, for there were some assumptions made here.  All
were made rather conservatively, however, and I do believe the numbers are,
if anything, too small.

	First of all, not all of the butterflies I killed were on my grill.
Most bounced off the car, or were destroyed by the strong air currents the
car created.  What I did was to count the number of butterflies that I could
see being destroyed by my car in 60 second intervals.  I did this many times
throughout the 2 day period, and at different places.  The numbers I quoted
were all averages.  At times, the numbers were much higher.  At other times,
they were lower.  On Saturday, the average was only 16/minute.  On Sunday,
the number was 38/minute.  Collisions of 8 butterflies at an instant were
common on Sunday.  This made it very hard to count, so I suspect my numbers
are low.

	Secondly, the number of butterflies in flight was astounding (to the
likes of me).  As I wrote in another post, the dead were piled in heaps
along the roadsides and center dividers.  My windshield was a total mess of
bug guts.  The butterflies consisted of many species, although the American
Snout, the Lyside Sulpher and the Queen made up the biggest percentage (like
95%).  The dominant species was somewhat geographically dependant, but all
three of these were common along all stretches of highway.  There were
swarms of other species (like the Variegated Fritillary), but for the most
part this was a heterogeneous mixture of Leps in motion.

	Third, I took these averages along the roads that I traveled and
assumed the same density on all major highways.  I traveled from Houston on
highway 59 all the way to Laredo.  The butterflies started flying in numbers
by 9:00 a.m., and didn't stop until after dark (7:30?).  I also drove on 83
to Pharr, and back to Houston on 77.  While highways, they are not
Interstates, and the traffic was not all that busy.  I stopped to count cars
on several occasions, taking averages for these as well.  The assumption of
a continuous stream of cars (at this average density) on the approximated
highway miles is obviously suspect, but again I do believe that the numbers
are conservative.  I also limited the geographical area to that bounded by
my travels, and clearly the butterflies are not so constrained.

		At any rate, there must be a lot of butterflies where you
	driving, despite mankind's effect on their habitats...

	Most of the habitat in this area is fenced and gated ranch and oil
property, and therefore mostly undisturbed (the cattle seem to live off of
naturally occurring flora).  Unfortunately, the amount of undeveloped public
land is extremely limited, and because of this the counts of endemics and
rare strays from Mexico are biased (since they take place mostly on
parkland).  I'm sure collecting is considered taboo by many local
environmentalists and ecologists for this reason.


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