It's very interesting to use historic records for comparison to modern-
day conditions. Sometimes they got it wrong, as in V.C. Allison's
case, but sometimes there's great value in looking up old information.
I just purchased from National Geographic Magazine's stock archives a
photograph of the Dome Room in Carlsbad Caverns. It ran in the Sept.,
1925 issue and is the first color underground photograph ever made. In
it, the formations in the chamber are colorful, with rich golds and
red-browns. I believe the colors are fairly true, because the color of
the human model in the photograph is not saturated. Today the Dome
Room is very bleached, almost like an old bone. It appears that
Carlsbad Caverns was much more colorful when it was first discovered.
I expect that the increased air flow caused by the elevator shafts
(before airlocks were installed) did a lot of the damage, especially
when combined with regional drought patterns. The Dome Room is very
close to the elevators.
Lois Manno
On Jan 25, 2009, at 7:21 PM, Minton, Mark wrote:
Interesting application of modern science to an old rumor
about how many bats there were in Carlsbad Cavern: <http://www.sciencenews.org/view/generic/id/40178/title/Carlsbads_8_million_lost_bats_likely_never_existed
>.
Mark Minton
Carlsbad's 8 million 'lost' bats likely never existed
Thermal imaging and algorithms challenge famous estimate
By Susan Milius
Web edition : Friday, January 23rd, 2009
Eight million is a lot of bats to lose, and now a new study may
explain what happened to the possibly lost bats of Carlsbad Cavern.
Short answer: According to a Boston University team, the famous 8
million bats never existed in the first place.
From spring to fall, the cave Carlsbad Cavern in New Mexico’s
Carlsbad Caverns National Park still hosts hundreds of thousands of
migratory Brazilian free-tailed bats that thrill visitors by boiling
out of the cave at dusk for a night’s foraging. All the bats
roosting in the cave emerge in a dense plume that streams on and on
and on, sometimes for an hour or three.
As with many wildlife spectacles these days, always present is the
disturbing possibility that today’s show is a mere wisp compared to
the great Carlsbad bat clouds of yore.
In 1937 V.C. Allison published an estimate of the Brazilian free-
tailed bat numbers based on timing an emergence (14 minutes at great
density; four minutes at half that) and eyeballing the speed and
size of the stream. About 8.7 million bats roost in the cavern, he
reported.
Since then, methods and numbers have varied, but estimates haven’t
topped a million. Consequently, conservationists have raised alarms
about perils to bats. Or maybe Allison’s eyeballs played tricks on
him, or the great emergence flights really have shrunk drastically.
Starting in 2005, bat scientist Thomas Kunz of Boston University and
colleagues brought new technology to Carlsbad Cavern to count and
observe the animals. Parts of the cave where bats roost are closed
to visitors to prevent disturbances to the animals. But to improve
the census and studies, the park allowed Kunz’s team to venture into
these portions of the caves.
One of the first field biology groups to use military-derived
thermal imaging, Kunz’s team attracted the U.S. Park Service’s
interest by pointing out that the researchers didn’t need to shine
any lights, even at infrared wavelengths, on the bats; the cameras
detect heat directly.
“Surreal” and “disgusting, yet absolutely amazing” is how Nickolay
Hristov, now at Brown University in Providence, R.I., describes the
roosting sites. “Imagine standing on a 20- to 30-foot cushion of bat
poop covered with a constantly moving carpet of dermestid beetles
and their larvae,” he says.
“As you move around you are being rained on by bat urine,” Hristov
says. Bat excretions don’t have the same odor as human equivalents,
he says, but “the smell of ammonia is so strong that your eyes
burn.” A single bat barely makes any noise that humans can hear but
tens of thousands of them together get “quite loud,” he says. ”I
would grab the camera and go back in a heartbeat.”
To count the bats emerging, the researchers set up cameras around
the cavern mouth to get a clear view of the stream. Magrit Betke of
Boston University’s computer science department developed algorithms
for analyzing the camera’s recordings. Her work basically allowed a
computer to pinpoint bats as spots in a camera frame and then track
the spots across enough frames to confirm the dots were indeed bats.
The analysis ends up with a count of each spot in the vast stream.
In a series of counts in 2005, numbers varied from a low of not
quite 70,000 as bats started to arrive from their southern winter
caves, to a peak about 10 times higher weeks later as migrating bats
on their way elsewhere took shelter.
Even at the peak, counts came up some 8 million bats short of the
old estimate. So the Boston team used the Brazilian free-tails’
average 0.28-meter wingspread to model how many bat wing-beat
“spheres” would fit through the cavern in a minute.
A choke point inside the cavern narrows to only 120 square meters,
and bats don’t fly wall-to-wall. At most, 50,000 bats per minute
could fit through that choke point and emerge from the cavern mouth.
Thus a single million would be closer to the number of bats possible
that wowed Allison.
For 8.7 million bats to have flown through the choke point in 18
minutes, as Allison reported, the densest crowd would have had to
pass through at 500,000 bats per minute. Their wings and bodies
would have had to pass through each other to somehow squeeze through
the passage.
“The Boston study clearly shows there’s no physical way that could
happen,” says Renée West, supervisory biologist for Carlsbad Caverns
National Park. “That’s a relief.” The park has discounted Allison’s
numbers as excessive, she says, and she’s glad to have the new
analysis.
“That doesn’t mean these bats aren’t declining,” Hristov says. “The
declines just haven’t been as bad.”
And for the cavern’s human visitors, hundreds of thousands is still
a lot of bats.
_______________________________________________
NMCAVER mailing list
nmca...@caver.net
http://caver.net/mailman/listinfo/nmcaver_caver.net
_______________________________________________
NMCAVER mailing list
nmca...@caver.net
http://caver.net/mailman/listinfo/nmcaver_caver.net
