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Research in Carlsbad Caverns National Park Scientific exploration and discovery

Research in Carlsbad Caverns National Park in Carlsbad Caverns National Park Carlsbad Caverns National Park provides unparalleled opportunities to see south-western wildlife, desert

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Page 1: Research in Carlsbad Caverns National Park in Carlsbad Caverns National Park Carlsbad Caverns National Park provides unparalleled opportunities to see south-western wildlife, desert

Research inCarlsbad Caverns National ParkScientific exploration and discovery

Page 2: Research in Carlsbad Caverns National Park in Carlsbad Caverns National Park Carlsbad Caverns National Park provides unparalleled opportunities to see south-western wildlife, desert

ABOUT THE COVER

Mexican free-tailed bats have roosted on theceiling in Carlsbad Cavern for over 5,000years. Within the past 50 years their numbershave declined from several million to about500,000.

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Research inCarlsbad Caverns National Park

Carlsbad Caverns National Park providesunparalleled opportunities to see south-western wildlife, desert plants, majesticlimestone mountains, and hidden caves.The park is many things to people whocome here to experience its wonders. It isespecially important to scientists as aplace to investigate cave geology, as wellas desert plants and wildlife. It is aunique, protected natural area, shapedlargely by natural processes.

The following science articles provide aglimpse of the research being done inCarlsbad Caverns National Park. Thisresearch is often a cooperative effortbetween federal and state agencies, withvaluable contributions from universityscientists, students, and other partners.The park resource management staffinventories and monitors importantresources such as bats, mountain lions,migratory birds, and endangered cactus.Other scientists are conducting in-depthinquiries into cave geology, water quality,paleontology, microbiology, mammalogy,and fire ecology. These articles will sharea brief but important picture of scientificdiscoveries that have emerged throughthe efforts of dedicated researchers overthe past five years.

The park is entrusted to conserve caveresources, thus preserving a precious partof our national heritage. For more than75 years, the National Park Service hashad a dual responsibility to conserve theresources of the national parks andprovide for their enjoyment by theAmerican people. Increasing numbers ofvisitors and a myriad of influences fromthe modern world are turning this dualmission into a battle. Today some of thedistinguishing features and resources ofCarlsbad Caverns National Park are injeopardy. These threats require monitor-ing of ecological conditions and applica-tion of science-based management toprevent further resource degradation.Existing data and new information iscontinuously integrated into resourcestewardship efforts.

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Carlsbad Caverns, Underground World

The caves of Carlsbad Caverns NationalPark contain sites with exceptionalnatural beauty. The park’s most famouscave, Carlsbad Cavern, is over 1,000 feetdeep and currently contains 30 miles ofmapped passages. The Big Room ofCarlsbad Cavern is the largest under-ground chamber in the United States.Massive stalagmites, stalactites, columns,flowstone, travertine, and cave “popcorn”decorate the room. The park’s largestwildlife attraction is a colony of Mexicanfree-tailed bats, numbering in the hun-dreds of thousands, that live in the cave.The colony spends six months eachsummer in the cave where their youngare born.

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The park protects Lechuguilla Cave, thedeepest limestone cave in the UnitedStates. Here the superlative geologicalformations have astounded speleologistsfrom around the world. The world’slargest collection of bacterially-assistedbiothems exist in the cave. Recentresearch has revealed unusual microbesin pools—suspected lithotrophic bacteriathat derive metabolic energy from sulfur,manganese, and iron. More than 1,200strains of microbes from pools, soils,corrosive residues, and sulfur depositshave been isolated.

In all, the park has 85 caves with a totalof over 136 miles of known passages androoms. These caves contain some geo-logically unique and rare cave forma-tions. This area contains one of thebest-preserved, exposed Permian Agefossil reefs in the world. The park cavesprovide a unique opportunity to view afossil reef from the inside.

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The Guadalupe Mountains of southeast-ern New Mexico preserve an excellentfossil record of Permian Age (250 millionyears ago) marine life. The GuadalupeMountains are the uplifted remains of anancient reef which developed around theperimeter of a shallow sea. Unlikecontemporary coral reefs, this reef wascomprised of the skeletons of calcareoussponges and algae. At the time of thereef’s development, corals were not anabundant species. By studying the fossilrecord, we can learn more about ancientmarine ecosystems.

Dr. Kevin Rigby of Brigham YoungUniversity described several fossilsidentified for the first time within Per-mian rocks in North America at CarlsbadCaverns National Park. The largest fossilsponge known from the Permian Age wasdiscovered near the entrance of CarlsbadCavern.

By examining the structure of fossils, Dr.Fagerstrom of the University of Coloradoreports that Sphinctozoa sponges devel-oped from a seafloor-dwelling species toa reef-builder through the thickening ofthe sponge’s walls and internal structures.This increased structural mass allowedthe sponges to withstand the forces ofwave action and create a base skeletonaround which the reef developed. Siltsand broken skeletal pieces becametrapped within the structure and ce-mented into place by algal mats.

Carlsbad Cavern offers both researchersand the public an interesting view of theinterior of an ancient reef. From thisperspective, we gain insight into theprocesses which created the backbone ofthe Guadalupe Mountains. Throughcontinued research we gain a betterunderstanding of the Capitan Reef andthe Permian Age.

Living Reef to Limestone Rock

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Lechuguilla Cave was known for years asMisery Hole, a 400-foot long cave whichwas mined for guano in the early part ofthis century. For years, those enteringnoted a wind which issued from a rubblepile within the cave, yet it was not untilMay of 1986 that an entrance was dugthrough the rubble to an unexplored cavebeyond. Since the breakthrough, Lechu-guilla Cave has yielded over 89 miles ofpassages and numerous mineralogical,geological, and microbiological discover-ies. The cave is 68 degrees Fahrenheitwith 99% humidity.

For thousands of years, the only influ-ences from the surface came from waterseeping through the rock (no flowingstreams) and the air which the caveinhaled or exhaled according to changesin barometric pressure outside. In thisrelative isolation, a separate and uniqueecosystem developed which supported itsown brand of life. This cave first ap-peared to be uninhabited, but life existsinvisible to the naked eye. Dr. LarryMallory, a former University of Massa-chusetts professor, has started studies ofmedicinal uses of newly discoveredmicrobes in Lechuguilla.

The unique conditions found in Lechu-guilla Cave have given rise to adaptationof certain microbes to allow them tosurvive in this cave’s environment.Without sunlight or a consistent organicfood source, life in this cave has beenlimited to microbes capable of reducingminerals for energy and to microbes whoeat these primary producers. Most of thelife is contained within the cave’s pools,concentrated at the “bathtub ring” aroundthe pools where the air, water, and rockinterface. The limited availability of foodhas dictated severe competition, and eachpool within the cave has developed itsown distinct population of microbes,

most of which have never before beenidentified.

With his interest in medicinal uses formicrobes, Dr. Mallory hypothesized thatthe scarcity of food likely caused thesemicrobes to develop means for eliminat-ing their competition. This survival tacticcould be in the form of a compoundwhich one microbe may produce to killoff other nearby microbes. So far, afterfour years of sampling, over 1,000microbial strains have been discovered inLechuguilla’s pools. This research hasprovided the park with a new understand-ing of the cave’s fragile ecosystem, aseach pool appears to be different fromany other.

In order to evaluate the changes inLechuguilla due to human explorations,Ms. Diana Northup, a researcher with theUniversity of New Mexico, has initiateda study to determine the extent of humanimpact. Exploration and research inLechuguilla Cave often requires multi-day trips. Certain microbes would bepresent in this cave environment onlythrough human introduction. By testingareas that haven’t been visited for sometime, we can learn whether or not thecave recovers from such disturbances.Although bacteria contaminations werefound within the cave, populations dodecline with time.

Life, as we are learning, can be found inthe most unexpected of places, and wemust be careful in our activities to avoidaltering a balance achieved only by time.The challenge now is to incorporate whatis currently known about LechuguillaCave into a management plan thatprotects this valuable resource.

Microbes Below the Surface

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Cave Bacteria and Life on MarsThe Viking space craft 20 years ago failed to find conclusive evidence of life on the surfaceof Mars. Despite this evidence, some researchers believe that microbial life may now existunderground on Mars, sheltered from the hostile surface environment.

We know that microbial communities on Earth have adapted to an amazing array of hostileconditions. Bacterial life can be found in boiling hot springs, or in the flares of active volca-noes, and even deep underground.

Dr. Chris McKay and other NASA scientists have come to Lechuguilla Cave in CarlsbadCaverns National Park to study microbes that survive in a sulfurous environment similar towhat may be found on Mars. What makes this study so intriguing is that some bacteria heremay derive energy from sulfur. The group of scientists continues to study the bacterial andfungal ecosystem of the cave and speculate whether similar life forms survive on Mars.

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At Carlsbad Caverns there is a large,active colony of roosting bats with along-term occupancy record dating back5,000 years. At nearby Lechuguilla Cave,scattered evidence of seven different batsspecies were found. Current studiesindicate that bat bones found in Lechu-guilla Cave are significantly less than10,000 years old. Carbon-14 dating ofseveral guano sites and bat bones mightgive us some insights into what happenedin Lechuguilla Cave with regard to thetime when bats were present.

In the entrance pit of Lechuguilla Cave,there is a deposit of guano, but few batskeletons. Until 1985 the known entranceended in a jumble of rock rubble, calledbreakdown. Since then over 89 miles ofnew passages have been discovered. Batskeletal remains were collected alongsome passages. Ms. Pat Jablonsky,director of the Carlsbad Museum, hascollected over 50 osteological specimensof bats for the purpose of scientificidentification. How did these bats getinto these blocked passages?

It would appear that at some point in thecave’s history, there may have been moreentrances into this vast undergroundsystem of passages; over time, theentrances became sealed. There isspeculation that the bats entered the cavethrough small cracks in rock crevices onthe surface while looking for day roosts.They crawled into these cracks farenough to come into contact with portals,only to fly around and lose their wayback to the tiny entrance cracks.

Numbers of Bat Skeletons Found inLechuguilla Cave 1991-1996Name Species #

Long-legged Myotis Myotis volans 11

Yuma Myotis Myotis yumanensis 2

Western Small-footed Myotis Myotis ciliolabrum 26

Cave Myotis Myotis velifer 1

Big Brown Bat Eptesicus fuscus 1

Hoary Bat Lasiurus cinereus 2

Townsend’s Big-Eared Bat Plecotus townsendii 7

Bat Skeletons, Glimpses into the Past

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Proper, careful documentation of a caveis important in determining its signifi-cance and scientific value. Cave mappingis the foundation for any type of caveresearch. Since the 1960s CarlsbadCaverns National Park has had coordi-nated survey groups for both our remotecaves and Carlsbad Cavern.

May 1986 marked a major breakthroughwith the initiation of the largest cavemapping project ever undertaken here—Lechuguilla Cave. Under the guidance ofpark cave resource specialists, and thetwo volunteer cave survey organizations,Lechuguilla Exploration and ResearchNetwork (LEARN) and the Cave Re-search Foundation (CRF), survey stan-dards were established. Surveying in acave is quite different from surfacesurveying. Dragging a theodolite, rod andchain underground is neither practicalnor feasible in most cases, and can causesevere resource damage. Hand-held ortripod-mounted precision instrumentssuch as Brunton compasses and incli-nometers, along with a 100-foot tape, arethe acceptable choice among cavesurveyors. Each survey team usuallyconsists of four people, a sketcher, aninstrument person, a lead tape person,and one person taking inventory of cavefeatures. The collected data is thenentered in a computer mapping programand database.

Recently cave mapping has taken a newturn with the Geographic InformationSystems (GIS). Carlsbad Cavern ispresently going through a renaissance asmost of the cave is being resurveyed.Archeological, historical, biological,paleontological, and mineralogical siteswill be tied in to the nearest surveystation. For example, we can make aquery through ArcView and illustrate allthe survey stations that have recordedaragonite crystals. GIS for cave manage-ment is limited only by the imaginationof the one making the themes of inquiry.

The 1996 map of Carlsbad Cavern endedwith 30.85 miles of mapped passage,while the 1996 map of Lechuguilla Caveended with 89.35 miles of mappedpassage. However, by the time the nextcave map is completed, Lechuguilla’slength should far exceed that figure. Itwill be interesting and exciting to see thesurvey results by the next millennium.

Mapping Underground

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From the early days of guano mining tolater development of the park for tourism,degradation of cave features occurred.Park caves are extremely fragile. A goalof park management has been to evaluatepast impacts to the caves and wherepossible restore damaged cave features.Volunteers have played an important rolein helping conserve and restore caves.

In Carlsbad Cavern the construction andmaintenance of trails, the blasting ofelevator shafts, vandalism, and themillions of visitors have changed thecave environment. Most of the main trailsthrough the cave are self-guided; conse-quently, vandalism is a problem. Between1985 and 1993 thousands of small caveformations were broken and/or removed.Stainless steel handrails are now beinginstalled along both sides of the pavedtrail as a deterrent to vandalism and off-trail travel.

Rubble left from the blasted elevatorshafts is slowly being removed from thecave. Underneath the rubble flowstone,rimstone dams, and other features aremiraculously intact. Mud has beentracked over flowstone or into cavepools. These areas are identified andslowly restored back to their originalstate by volunteer workers.

For many years dust and lint have been

slowly accumulating, by the 1990s it washanging in large globs in places andcovering most surfaces. Close evaluationrevealed this accumulation of lint wastrapping and holding moisture, slowlydissolving cave formations. It is esti-mated that eight to ten pounds of lint areleft behind in the caverns every year byour 600,000 visitors. Volunteer workershave meticulously removed much of thismisplaced material.

The discovery of Lechuguilla Cave in1986 stimulated new approaches to theconservation of pristine cave environ-ments. New exploration guidelines havebeen developed to minimize impacts.Clean gear and clothes, the use of non-marking boots, and numerous otherprotocols have been developed for caversin Lechuguilla and other fragile sites.

Care of cave formations in the early1900s was lacking. Caves were nottreated as precious nonrenewable re-sources. We have come a long way in ourmanagement of these nonrenewableresources. The concept that once theseresources are broken and gone, they willnever return, is a sobering one. Over thepast few years, many experiencedvolunteers have donated thousands ofhours to help restore and conserve thecaves of the park. Their efforts areappreciated in our endeavor to restorepark caves. Future generations deserve tosee and experience these same caves in aspristine a condition as possible.

Restoration of Cave Environments

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Since the discovery of Carlsbad Cavernby cowboys in the late 1800s, humanshave been directly affecting this world-famous cavern by building trails, exca-vating shafts to remove guano, andplacing numerous structures over thecave. These structures include a visitorcenter, parking lots to handle largecrowds of visitors, a maintenance yardwith its associated gas tanks and pavedparking areas for trucks and other largeequipment, and a housing area withsewer lines, propane lines, and garages.Many of these structures are locateddirectly above the cavern.

When cavern development began in theearly 1900s—first for guano mining andlater for tourism—the area was ruggedand remote. A trip into the cave was anall-day affair. In those early days it wasconvenient and practical to build struc-

tures near the cave entrance. By the1930s the new road to Carlsbad Cavernthrough Walnut Canyon was completedand numerous buildings had been addedto the area above the cave, many ofwhich were built by the Civilian Conser-vation Corps. Sewer lines from the visitorcenter and other buildings ran to septictanks, while to the east of the visitorcenter and directly above Left HandTunnel excess liquids were sprayed outon the open ground. The last majorbuilding phase above the cave occurredduring the 1960s.

Carlsbad Cavern is located in limestonewhich was deposited in an ancient seaabout 230 million years ago. Everypassage in the cave is formed along afracture. In many places the fractures inthe limestone are very complex andformed an intricate maze of passages.

Risks of Cave Pollution

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Over time the cavern became the highlydecorated show piece of nature we knowtoday.

When our predecessors began to developthe area around the cave entrance, theywere unaware of how the cave formedand that their actions could damageCarlsbad Cavern. The very same frac-tures along which passages formed in thecave extend all the way to the surface inmany places.

The development over Carlsbad Cavernduring the last 90 years may threaten thecave itself. The sewer lines have leakedraw sewage down cracks and fissures inthe vicinity of the cave. The accumulatedoil, grease, transmission fluids, anti-freeze, and other contaminants fromhundreds of thousands of vehicles eachyear wash off the parking lots during rainstorms, disappearing underground. Ascientific study was conducted to tracecontaminant entry into the cave.

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Researchers from the Colorado School ofMines performed this infiltration study.Preliminary results indicate that waterdrips in Left Hand Tunnel have highnitrate values. This area is where theexcess liquids were sprayed out on thesurface and is where the main sewageline runs east and then south to thesewage lagoons. Either of these could bethe source of the nitrates. High levels ofaluminum and other metals have beenfound in numerous drips in the Big Roomarea. A possible source for these metalsmay be antifreeze and coolant materialfrom parking lot runoff.

Obviously, the removal of all man-madestructures from above Carlsbad Cavernwould slowly return the cave and the areaabove it to a more pristine condition.However, in order to provide for visitorenjoyment, less drastic measures willprobably occur. A more likely scenario isthat this study will identify certainbuildings and practices that should berelocated off the limestone areas of thepark. The study should also make recom-mendations for modifications to facilitiesand operations that will reduce cavecontamination. Researchers will seek themost cost-effective methods of reducingthe greatest potential risks.

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12 Research in Carlsbad Caverns National Park

Cave Swallows (Hirundo fulva) have ex-panded their range northward into NewMexico. Cave swallows were first foundnesting in several caves in the park in the1950s. In 1966, two pairs of cave swallowsmade their nest in Carlsbad Cavern. Sincethen, the population has gradually in-creased to more than 2,000 birds.

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Life on the Surface

Carlsbad Caverns National Park is one ofthe few protected areas within theChihuahuan Desert ecosystem. What atfirst glance appears to be a sparse waste-land, actually provides habitat for a richdiversity of breeding birds, mammals,reptiles, and insects. The ChihuahuanDesert, the largest of four major desertregions in North America, holds surprisesfor the inquisitive. The region’s uniqueecological features create a living obser-vatory waiting for biological discovery.

More than 330 bird species have beenrecorded within the park. Most noticeableare the circling turkey vultures, but alsorecorded within the park boundaries are37 different warblers. The cavern sup-ports the northernmost and largest colonyof cave swallows in the United States.Mammal diversity is equally impressive,with 76 species including mule deer, rocksquirrel, ringtail, and Mexican free-tailedbat. Carlsbad Cavern provides roostingsites for hundreds of thousands ofmigratory Mexican free-tailed bats.

The park is characterized by its relatively

high elevations, cool dry winters, hot wetsummers, and showy desert plantsincluding agaves, yuccas, cacti, sotols,and ocotillos. Many of the 800 plantspecies found in the park are at the edgeof their geographical distribution, includ-ing several threatened and endangeredspecies.

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especially important among mountainlions. With scent, lions advertise whetherthey are receptive to mating in addition toinforming other lions about the limits oftheir home range. They leave scent infeces, urine and by pawing and rolling onthe ground. Since 1988 park staff hasmonitored the mountain lion populationby documenting trends in the amount anddispersal of sign. Twice each yearbiologists travel the same trails keepingtheir eyes glued to the ground looking forsign. Scats are most prevalent, but tracksand scrapes can be found by the carefulobserver. Occasionally a lion-killed deerwill be found.

For many species precise estimates ofabundance are not practical. Thus “signsurveys” serve as a tool managers can useto keep monitor the population. Whilethere are a number of ups and downs,overall the amount of sign we haveobserved in Carlsbad Caverns NationalPark is stable. Preliminary results atGuadalupe Mountains National Park,however, suggest a significant declineoccurred between 1988 and 1996.

The state of New Mexico is currentlydevising statewide management plans formountain lions. The data collectedbetween the two National Parks will helpNPS managers speak intelligently aboutthe status and trends of the lion popula-tion in the Guadalupe Mountains.

Mountain lions (Felis concolor) roamsome of the most remote and ruggedcountry in the Guadalupe mountains.During the mid-1980s 22 mountain lionswere radio-collared in and aroundCarlsbad Caverns national Park. Biolo-gists estimated that an average of 58mountain lions roamed the 400 squaremile study area each year. About 40% ofthis population tended to be adults, with20% yearlings and 40% kittens. Adultmales averaged 120 pounds and hadhome ranges covering about 80 squaremiles. Adult females, on the other handweighed, about 70 pounds and rangedjust over 20 square miles. Male homeranges tended not to overlap. Femaleswere less territorial with other females,however, they avoided outright encoun-ters. Adult females usually reared twokittens every other year.

While some lions occasionally killlivestock, scats analyzed during the studyshowed that deer were the primary prey.Other natural prey included porcupine,rabbits, and small rodents. Overall, theremains of domestic livestock were foundin less than 8% of the scats. Still, about12 mountain lions are killed each yearunder depredation or preventativepermits in New Mexico outside CarlsbadCaverns National Park.

Scent marking is a common form ofcommunication between animals and it is

Mountain Lion Tracks and Trails

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Large mammals such as mountain lionsand mule deer invariably draw a lot ofattention, but at Carlsbad CavernsNational Park bats are also popular. Notsurprisingly, much information has beengathered on these groups of mammals.On the other hand, until recently almostnothing was known about the mostdiverse group of mammals inhabiting thepark--the rodents. Most information onthis group was based on a few museumspecimens and a publication written 67years ago called Animal Life of theCarlsbad Cavern by Vernon Bailey. Torectify this situation, the National ParkService funded a study in the early 1990sto determine the kinds, distribution, andrelative abundance of rodents livingwithin the park’s boundaries.

The survey confirmed the presence of 27rodent species including squirrels, pocketgophers, kangaroo rats, pocket mice,harvest mice, woodrats and porcupines.Six species were reported in the park forthe first time. Results of this survey willprovide basic ecological data for makingsound management decisions and fordesigning accurate interpretive programs.This baseline information can also beused for monitoring population trends ina group of mammals that serve as indica-tors of habitat quality in the park.

At present, information on all the park’smammals is being incorporated into anew book. The book contains a compre-hensive account of the natural history ofeach species found in the park. Besides27 rodents, the mammalian fauna in-cludes a shrew, 15 species of bats, tworabbits, 13 carnivores, and five hoofedanimals. The book contains detaileddescriptions of the park’s habitats fromdesert-scrub communities of the lowlandsto the pine woodlands on the highestsummits.

The Forgotten Mammals—Rodents

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Deep in Carlsbad Cavern, at a locationnearly 1,000 feet below the surface andover a mile from any known opening,lives a small colony of fringed myotisbats (Myotis thysanodes). Numberingaround 100 individuals, this maternalcolony roosts just above Lake of theClouds, the lowest and warmest point inCarlsbad Cavern. Every summer eveninghundreds of thousands Mexican free-tailed bats (Tadarida brasiliensismexicana) fly out of Carlsbad Cavern tofeast on flying insects. Do fringed myotisbats exit among the massive outflight ofMexican free-tailed bats?

Resource managers needed to know whatroute fringed myotis bats used to reachthe above ground desert environment.They were also interested in other basicinformation that might aid in conservingthis rare species, such as the time ofemergence, the duration of exit flight,and destination drinking water sources.Thirteen fringed myotis were fitted withtiny transmitters. The transmitters weighonly one-eighth of an ounce and wereaffixed to the bats with a glue thatdeteriorates in about ten days. Thetransmitters enabled researchers Dr. KenGeluso and Dr. Troy Best to follow theirexit from the cave.

Researchers found that most fringedmyotis exited out the main cave entranceamong the Mexican free-tailed bats,although a few departed through asmaller natural entrance. This smalleropening, located some 200 yards fromthe main bat exit point, is surrounded bya fence to keep people from falling in.Researchers found that some bats flewinto the fence and got caught. Followingthis discovery, park maintenance workersrepositioned the fence farther from theopening to allow the bats to gain moreelevation before heading off to desertfeeding and drinking locales. It was alsofound that cave lights left on in thebelow-ground lunchroom due to emer-gency maintenance, delayed emergenceof the fringed myotis by up to two hours.The lights likely altered their flight paththereby sending some bats to remote cavepassageways. Park cave staff nowdiligently turn out all lights at the end ofeach day.

This research was funded with a grantfrom the Adopt-A-Bat program, a non-profit fund derived from donations thatsupports bat conservation, education andresearch.

Fringed Myotis—Unnoticed in a Bat Crowd

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The evening flight of Mexican free-tailedbats (Tadarida brasiliensis mexicana)from the entrance of Carlsbad Cavern isone of the park’s principal visitor attrac-tions. Free-tailed bats are a colonialspecies that feed entirely on insects. Thecolony at Carlsbad is comprised prima-rily of females who give birth to theiryoung from June through July beforemigrating south in October to winter inMexico.

This colony declined from an estimated8.7 million in 1936 to approximately200,000 in 1973. Similar declines havebeen noted throughout the SouthwesternUnited States and Mexico. It is thoughtthat the Organochlorine pesticide DDTwas the primary cause. Dr. Donald Clarkfrom Texas A&M University is evaluat-ing DDT levels in specimens of batscollected from this colony prior to the1950s. This may verify or refute the roleof DDT in the decline.

Colony size has been estimated using avariety of techniques ranging from purespeculation to fairly complex calculationsof the duration, intensity and velocity oftheir exodus from the cave. Unfortu-nately, no method has provided a mea-sure of statistical precision, therebycomplicating trend or cause and effectanalysis.

How Do You Count Nearly a Million Bats?

The evening flight of

Mexican free-tailed bats

from the entrance of

Carlsbad Cavern is one

of the park’s principal

visitor attractions.

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Resource managers and several coopera-tors at Carlsbad Caverns have completedyear one of a multi-year project todevelop a reliable way of monitoring thislarge bat colony. Two methods arecurrently under investigation. The firstmethod entails taking infrared photo-graphs of the colony while they hang onthe cave ceiling. This method willprovide a reasonably precise populationestimate. The second method, which is anindex, utilizes sound recordings of thebats as they travel through the cave.

Photo monitoringIn 1996 infrared photographs were takenfrom 15 permanent points over fiveconsecutive days during the spring andagain in the fall. This allowed withinseason and within year variations to beevaluated. Photographs were thenoverlaid with a gridded transparencysized for each photo point. Grid sizecorresponds to a square foot on the caveceiling. We then used the lower range ofpublished densities (200 bats per squarefoot) to calculate a conservative estimateof the population. Bats roosting in cracksand fissures in the ceiling are hiddenfrom the camera’s eye, thus we feel thismethod produces a conservative estimateof the population.

We estimated the spring prebirth popula-tion to be about 193,000 bats. As ex-pected, the population nearly doubled to352,000 bats by fall when the young wereflying.

Engineers with the Department of Energyused laser technology to create a con-toured map of the ceiling. Contours willcorrespond to varying ceiling heightsthereby providing more accurate esti-mates of ceiling area. Each year thephotos will be scanned into a computerand the contour map will be displayed asan overlay. Using GIS software, scientistscan sum up the area of bats withincontours for a more precise and unbiasedestimate of the total area covered by bats.Eventually, biologists hope to verify theaverage number of bats packed into asquare foot of cave ceiling at CarlsbadCavern. However, the photo monitoringwill be useful for monitoring trends evenwithout exact numbers.

Sound recordingsWe are experimenting with the use of aremote microphone to record the soundsmade by bats flying in and out of thecave at night. A data-logger allows us torecord the sound, measured in decibels,once every second. This data set is thendownloaded to a computer and graphedfor a permanent “signature” of the night’sactivities. The area under this curve,aptly dubbed “bat units”, is theoreticallyproportional to the number of bats thatfly. Eventually we hope to correlate thissound signature with estimated abun-dance from the photo-point method.

Sound recordings taken throughout thenight have the additional benefit ofhelping us understand bat behaviorduring various seasons, weather patterns,or disturbances.

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Brown-headed cowbirds, (Molothrusater) are brood parasites. Brood parasitesdo not construct nests of their own, ratherthey lay their eggs in the nests of other“host” species. This particular behavior isnot unique to the brown-headed cowbird.In North America, bronzed cowbirds,yellow-billed cuckoos, and black-billedcuckoos are also known to practice broodparasitism, although the latter two mostoften parasitize each other. Cliff swal-lows also practice a variety of broodparasitism, transporting eggs in their billsto the nests of other cliff swallows intheir colony.

Cowbirds have significantly expandedtheir range and have increased in abun-dance since the arrival of Europeans toNorth America. Originally residents ofthe Great Plains, where they wereassociated with roaming bison herds,cowbirds have greatly expanded theirbreeding range into improved habitatsuch as cleared forests, livestock grazing,agriculture, and irrigation. Whereascowbirds formerly parasitized approxi-mately 50 species, they are now known toparasitize at least 220 species. Cowbirdchicks usually require shorter incubationperiods than their host species, are oftenlarger, and more aggressively seek foodfrom the host bird. Thus nestling survivalof the host species is decreased.

Declines of migratory songbird species,due in part to brood parasitism by cow-birds, have been documented throughoutthe Southwest. Desert riparian areas areof particular concern as they are rela-tively rare, are isolated, and provideimportant habitat for breeding birds. NewMexico has lost approximately 90% of itsriparian habitat since European settle-ment, and over 50% of the avian specieslisted as endangered by the New MexicoDepartment of Game and Fish depend on

Nesting Bird Rustlers—The Cowbird

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were parasitized, including 0 of 24 Bell’svireo nests. The highest parasitism rate ofthe six parks studied was at Point ReyesNational Seashore (10.7%, 15 of 140).

In the upcoming year, biologists willagain monitor nests and conduct pointcounts to determine cowbird abundanceand use of the Rattlesnake Springs area.Cowbird eggs will be addled and re-placed in the nests of state or federallyendangered bird species (e.g., Bell’svireo and southwestern willow fly-catcher), to increase breeding success ofthese sensitive birds. Cowbird eggs willnot be addled or removed from non-listedhost species in order to determine theeffects of brood parasitism on hostsuccess. Long-term mitigation measures,such as cowbird removal by trapping orshooting, possible habitat improvementfor nesting birds, and irrigation practicesat Rattlesnake Springs will be criticallyreviewed, and recommendations madefor future management.

the remaining fragmented riparian habitatfor breeding or foraging. The riparianarea at Rattlesnake Springs in CarlsbadCaverns National Park provides criticalnesting habitat for many migratorysongbird species, including the NewMexico state endangered Bell’s vireo(Vireo bellii). Rattlesnake Springs is alsopotential habitat for the Southwesternwillow flycatcher (Empidonax trailliiextimus), a federally endangered speciesthat is likewise a preferred host ofcowbirds.

To determine the extent and effects of thecowbird problem at Rattlesnake Springs,park biologists have begun a program ofnest monitoring. During the spring andsummer of 1996 biologists discoveredbrood parasitism by cowbirds in 11 of 33(33%) observable migratory songbirdnests. Parasitism occurred in two of fiveobserved Bell’s vireo nests (40%).Cowbirds also laid eggs in the nests ofyellow-breasted chats, blue grosbeaks,house finches, and two unidentified neststhat were found containing cowbird eggsafter the host species chicks had fledged.Cowbird eggs were addled in all neststhat were still being incubated by the hostbird.

Overall, 78 nests were located in thestudy area. Of these, 67 nests belonged tospecies that brown-headed cowbirdsmight potentially parasitize, althoughsome only rarely. Many nests were toohigh (e.g., western kingbirds) or of such aconstruction (e.g., orioles), that it wasimpossible to observe the nest contents.

The brood parasitism rates at RattlesnakeSprings (33%) are high compared to ratesdiscovered during cowbird studies at sixother parks in 1995. For example, atOrgan Pipe National Monument, only 2of 110 nests available to cowbirds (1.8%)

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Wildland fires in Carlsbad CavernsNational Park are regularly ignited bylightning during summer thunderstorms.These prairie and woodland fires are welldocumented in historic records from thelate 19th century. Tree ring studies havedocumented fire scars hundreds of yearsback. Most of these fires were relativelysmall, but some will burn tens of thou-sands of acres.

Fire is the most influential ecologicaldisturbance of the park’s plant andanimal communities. Fire has played amajor role in shaping the grasslandswhich once dominated the park land-scape. Aggressive wildland fire suppres-sion and extensive grazing by domesticanimals have altered this grasslandecosystem. Grazing and fire suppressionhas favored the increased abundance anddistribution of shrubs and succulentdesert plants. Likewise, animal popula-tions have changed in response to thenew plant community structure reducingbiological diversity.

Prescribed fire is an essential tool in ourattempt to restore this out-of-balanceecosystem. First, some naturally-ignited(lightning) fires will be allowed to burnin the park when certain predefinedconditions (prescriptions) of wind speedand direction, relative humidity, and fuelmoisture are met. Second, prescribed(controlled) fires will be ignited atplanned locations by trained fire person-nel. These prescribed fires are conductedunder controlled conditions and moni-tored by professional biological teams.

Management-ignited prescribed fires areset at two or three locations each year.Fire-effects monitoring plots are ran-domly placed in each fuel model type.Every woody plant in these 10 by 30meter plots is identified. In addition, onehundred point intercept samples are takenalong one side of the plot for frequencyand density determination of grassspecies.

Along the park roadways you will noticea greater diversity of plant and animallife in the burned areas. Past researchindicates that carefully managed firesincrease the biodiversity of the park.Studies are underway on the effects offire on plant colonization and distribu-tion. The data will guide the park’sprescribed fire program which is aimed atrestoring fire as a force in shaping theecosystem.

Reintroducing Fire into the Ecosystem

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Stewardship of natural resources ispredicated upon collecting completeresource inventories that contribute to theunderstanding of park ecological condi-tions. Inventories of reptiles, birds, andmammals are underway at the park.These inventories are of critical impor-tance to generate reliable scientific dataon which to base park managementstrategies. For example, monitoring ofthe Mexican free-tailed bat populationwill help gauge bat recovery and habitatrestoration efforts. Bat numbers havestarted a slow rebound after their dra-matic decline in the 1950s; monitoringwill help document the extent of therecovery.

Natural Resource Stewardshipfor the Future

The park is developing a relationaldatabase of park resource informationthat will permit researchers to easilyretrieve information. When completed,this will be a tremendous asset to outsideresearchers and park managers.

Our partnership with caving volunteersand scientific organizations greatlyenhances our capacity to restore caveresources. Techniques to reconstructbroken stalactites, restore cave pools, andremove lint debris have been tested andaccomplished by volunteers interested inthe beauty and preservation of the caveenvironment.

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For anyone interested in conductingresearch or in receiving a list of ongoingresearch projects at Carlsbad CavernsNational Park, write:

Carlsbad Caverns National ParkResource Management Office3225 National Parks HighwayCarlsbad, New Mexico 88220

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Published by the Carlsbad Caverns Guadalupe MountainsAssociation and the National Park Service, 1997.

EditorGary Vequist

AuthorsHarry Burgess, Steve West, Jason Richards, Pat Jablonsky, BillRoute, Ken Geluso, Gary Vequist, David Roemer, Dale Pate,and Pat Mulligan.

DesignKelly Bridges

IllustrationsKim Van Zandt

Special thanks tothe many researchers and volunteers who have contributed togathering of scientific information at Carlsbad CavernsNational Park.

Printed on recycled paper.