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A puzzle from Carlsbad Caverns

Thanks to Mark Kaufman, who originally published this piece on Carlsbad Caverns National Park website: nps.gov/cave

The Mystery of the Sloth

It is not unusual to find ancient things in caves. These cool, dark, unexposed worlds are excellent at preserving the past, and in a diversity of ways. Caves in Lascaux, France, famously preserve the brilliant animal paintings of our Cro-Magnon predecessors. Carlsbad Caverns National Park is home to well over 100 caves – that are known – and some hold the remains of past life, such as the formidable dire wolf.

What seems a little unusual, however, is finding the remains of a massive ice age herbivore 400 feet down inside the Carlsbad Caverns. The Shasta ground sloth, although the smallest of all ground sloth species, reached 9 feet long and weighed a quarter of a ton. They wielded vicious sickle-shaped claws and a heavy, powerful tail.

These weapons, though, were likely used in defense. Sloths were meaty ice age herbivores, ideal prey for the fleet-footed cats and wolves of the period. Unlike the sharpened teeth of their predators, sloths had flat teeth, which they used to munch the plentiful vegetation that blanketed this once cool, damp land.

400 feet beneath the ground, however, there are no plants to eat. So what business does a sloth have in such an austere, lightless world?

Probably none.

Geologist Carol Hill, who helped to excavate the fossils, believes that the sloth entered the caverns alive, likely by falling in. “There hasn’t been a stream running through the Caverns for well-over a half million years. So it is unlikely that the sloth’s body, which we dated to around 110,000 years ago, was washed in.”

The bones are generally clean, and one would expect them to be covered in sediment if they were deposited by a stream or flood. Additionally, wrote Hill and Gillette in their analysis, “None of the bones appear to have been tumbled, rounded, or abraded by stream-current activity, nor is there any indication of scattering or damage by carnivores.”

The fall from the cave entrance is precipitous – early explorer Jim White used a rope to lower himself down the nearly vertical drop. So once down there, the sloth, who was not built for climbing steep walls, could not escape.

“The sloth was probably injured, frightened, and lost,” says Hill. Ultimately, it lay down to die in a pit beneath Devil’s Den, a place one travels through when descending into the caverns.

Looking into Devil’s Den today, we are pushed to wonder, did the sloth simply slip, or was there another contributor to the fall?

We know from other ice age sites, notably the Los Angeles La Brea Tar Pits, that wherever these ponderously moving herbivores roamed, cunning predators, fitted with long sabers and menacing claws, lurked nearby.

It is plausible, then, that the Carlsbad Caverns’ sloth did not fall in.

Perhaps it was chased.

Special Moments at Carlsbad Caverns National Park

I went to bat flight yesterday, the third time I’ve done so since the rumors started. This time, I had the amphitheater to myself. Quiet and cold, I sat, taking in the scene. I watched a sphinx moth feeding on the honey-scented algerita blossoms. I listened to a number of different birds hopping about, the distinctive canyon wren call, the last vestiges of cave swallows. I spotted a ringtail lurking above the entrance and was surprised by the bulk of a raccoon ambling up the trail. And then, the rushing brook of wings. Hundreds of bats, thin and steady, small puffs and clusters. Just me and the silence and the bats. I smelled the musk and watched for as long as I could bear the chill.

The foremost lesson I’ve learned from my time here is a lesson in silence. Relishing the quiet, observing the world about me and visitors alike. I’ve been practicing my lurking skills lately, picking up on and responding to cues. I was involved in an interesting iSWOOP yesterday. Three adult junior rangers and two zookeepers, one a wildlife biologist who has engaged in bat research and used thermal technology in porcupine studies (!). At one point, I just stepped back and asked her to talk about her interactions with bats. She talked about bat netting and counting, I talked about Louise’s research presentation, everyone interacted and shared and enjoyed the videos and pictures. We even had an extensive final discussion about technology’s place in the parks. —Christina Caparelli, Park Ranger


Hall of the White Giant Tour: Three Hours of Crawling and Scrambling

When you were little, did you make tunnels and hideaways with the couch cushions? For a week or two I had my own house made out of a refrigerator box. During snowy winters, I would work at digging tunnels into the pile of hard-packed snow the plow left at the end of the street. I gravitated to narrow, dark spaces.

As an adult, I see little reason to spend time crawling on my hands and knees in the dark in crevices. In general, I choose to be comfortable. Crawl into a dark place for fun? Only to crawl out again? Why?

As soon as I read the description of the Hall of the White Giant Tour, I knew that the experience was one I should try to avoid. Ladder climbing, slippery surfaces, and free climbing. Highlights include tight, narrow passages including Matlock’s Pinch. … prolonged amount of time spent in narrow cave passages. This trip is not recommended for anyone afraid of tight spaces or heights.

On the other hand, I am at the Caverns with a group. The iSWOOP team is mix of college students, a recent grad, and three educators closer to 40 than 20. We have disparate taste in food and a range of high to not-so-high energy levels. There’s not so much that we all do together and if touring remote parts of Carlsbad Caverns was going to be it, I was not going to be left behind.

Rangers will tell you that the area of the cave is not so remarkable as others in the beauty of its formations. When the chance to go on the tour came up, I made subtle attempts to have us choose a different expedition. They were rebuffed.

Never anticipating that this was to be part of the Carlsbad Caverns experience (because I thought we would be working non-stop and during my last cave crawling experience with teammates, I detected a dislike of cave crawling) I didn’t have the right clothes. Sundresses nor shorts would do. I needed to go to town for a pair of pants.

After visiting the sale rack, I donned my cheap, too red pants. I was ready. On the way into the cave I chatted with a volunteer who told me he never worries. I would like to practice that, not worrying, but in the meantime, I worried that I would be left behind. I took up a position close to the group leader.

We moved our bodies through narrow passages. Within the first fifteen minutes we had to clear Castration Rock. As we crawled along by the light of our headlamps, it was hard to banish the image of Winnie the Pooh stuck in Rabbit’s entry. As I recall, Rabbit slung a dishtowel over Pooh’s leg, which was protruding into the kitchen of his burrow. And on the forest side of the hole, Pooh endured miserable weather until finally his waistline shrank enough for him to leave for home.

I wished for a snake spine. Without relying on arms or legs, a snake can move itself forward. I wished for claws that would hold the surface. I quickly resorted to using my knee pads to gain traction when my boots slid off the rock surfaces.

Ranger G, our tour leader, goes first and points out hand holds and toe holds, but it’s dark and there are two people between Ranger G and me. Louise passes on the information, but sometimes I have to make it up as I go.

Ladder on.


Ladder off.

That wasn’t bad, but I’m no good at ropes. We wait. Only one person is to be on the ropes at a time. Thank heavens for gloves. I use all the strength in my legs and make it, slowly, up.

We marvel at a cave cricket. Other than us, until now, we have seen nothing alive. Other than rock surface, very little is visible to our naked eyes. But researchers are documenting the millions of microbial beings at work in caves. Diana Northup has visited parts of the cave system at Carlsbad Caverns that I will never see. I can’t imagine myself descending on a rope into the dark, hiking for at least a day, and camping out in a light-deprived environment. Even though we aren’t picnicking or littering, Diana makes that the point that we have a huge impact on caves by the very fact that we go in and bring ourselves. As we walk through a cave we shed tens of thousands of skin fragments a minute. I try to picture it. We each are a moving snowstorm of microbes, leaving behind us a pile of debris. Not just skin cells, say we have some remnant of dinner on our clothes or in a beard, we could be dropping food crumbs. To a microorganism it’s as through you dropped a supermarket on top of its head. It’s probably a big deal for a cave cricket too.


I read a transcript from a Nova episode recently where researchers nicknamed microbes, which tolerate extremes of pressure, heat and darkness “extremophiles.” No sunshine needed. The story of microbes in action is a good one. For years and years everyone assumed that carbonic acid had hollowed out the caves, but sulfuric acid is much more powerful than carbonic acid. Because it’s much more powerful, it makes more sense as a factor in the formation of a cave system of this scale. But I read that you very rarely find it in nature.

Carol Hill and David Jagnow were interested in finding a source of sulfuric acid. Carol Hill knew that if hydrogen sulfide mixed with oxygen it would create sulfuric acid. Bingo. But what was producing the hydrogen sulfide gas? Researchers knew that hydrogen sulfide gas was prevalent. Every drilling effort in the Carlsbad Cavern area releases the smell of rotten eggs–hydrogen sulfide gas! Turns out, tiny microbes, feeding on oil far beneath the cave, produced hydrogen sulfide gas as a product of their metabolism. The gas seeped up where it mixed with oxygen in the ground water and formed sulfuric acid. The acid ate away vast amounts of limestone, carving out the caves. Startling! Biological processes, not just the expected geological and chemical processes had shaped the world beneath our feet.

That’s history. You can’t smell hydrogen sulfide now. Because the hydrogen sulfide is being produced way below the deepest parts of the caves. In most instances the gas doesn’t reach the water table and it is the ground water rising toward the surface that is a vehicle for the reaction. What about microbes today? Are they active? Researchers from the University of New Mexico and New Mexico Tech are still identifying the microbes present at Carlsbad Cavern and at other cave systems. How do microbes sustain life in this sunlight deprived environment, in areas where humans don’t bring in nutrients? What if the main food source is minerals? Northup and her colleagues have shown that some microbes are literally eating the walls.

On the way back I realize that someone ahead of me could get stuck or injured. If so, eating the walls is probably not an option for me. Furthermore, I’d prefer not to be waiting in an awkward position in a space so tight that I can’t shift my weight. This anxiety presses against my chest and I begin to hang back rather than attempting to keep up with the person ahead of me. Just in case.

Later I read American Caving Accidents, 2011-2012, a magazine with riveting reports of near tragedies. Each accident is described in detail followed by a mini-sermon. These take-home messages are irresistible if sometimes obvious. “Brighter lights often equal greater safety, especially when tired or otherwise stressed or compromised.” “The importance of a good, reliable surface watch can never be over-emphasized.”

There is little else on my mind during this tour. I’m not thinking about my to-do list or regrets from my first year teaching or my interactions with my boss in 2004. I’m focused solely on the parts of me that need to work together in this challenging environment. When someone offers a suggestion that is meant to be a joke, I almost follow it. I am so intent on taking every suggestion seriously. But no, it can’t be better to touch the rope as little as possible. I laugh; we’re giddy. And soon we’re out. With sore muscles, surprised by the light and the headroom, taken aback by night sounds in the park. Relieved and maybe a little disappointed to have left the close quarters. But now we can go back to our devices and maybe I’ll reread some more about the SLIME (Subsurface Life In Mineral Environments) Team and their current studies investigating how microbes are involved in forming caves www.caveslime.org.—Martha Merson, iSWOOP Project Leader


American Caving Accidents, 2011-2012. The Journal of Record for Caving Accidents and Safety Incidents in North America. A special publication of The National Speleological Society. http://caves.org/pub/aca/

Canyons and Caves (2008). A Newsletter from the Resources Stewardship and Science Division. Issue 38. http://www.nps.gov/cave/planyourvisit/upload/C&C38.pdf.

The Mysterious Life of Caves (2002). http://www.pbs.org/wgbh/nova/transcripts/2910_caves.html

Northup, Diana. Microbes and White Nose Syndrome. Talk: Carlsbad Caverns, June 2014.

Northup, Diana. 2009. Sight Unseen: Microbial wonderland of caves. Societià Speleologica Italiana.