I went out in the desert to find a strange fungus that's killing millions of frogs in North America

I went out in the desert to find a strange fungus that's killing millions of frogs in North America

This is a canyon tree frog, Hyla arenicolor. Its main method of avoiding predators is camouflage. As a result, the canyon tree frog comes in a very wide range of colors, patterns and even textures depending on what its home range looks like. Canyon tree frogs, as the name confusingly suggests, are not often found on trees, but near water, on slot canyon walls throughout southern Utah, to Colorado and down to Central Mexico (Behler & King, 1979). 

In the summer of 2022 I was part of a research team with the goal of locating Hyla arenicolor. We were a scrappy bunch of Natural-Science Biology students led by Dr. Kurt Walker, PhD of zoology and masterful frog finder. He has been monitoring local populations of canyon tree frogs since 2012. It started out, somewhat accidentally, as a project to monitor a destructive species of chytrid fungus, Batrachochytrium dendrobatidis (Db). 

Db, is a chytrid fungus that infects the skin of amphibians and destroys the protective mucus layer that they rely on to keep their skin from drying out (Fisher & Garner, 2020). It likely comes from East Asia, where it has been infecting amphibians for about 50 million years (Kupferberg et al., 2021). Amphibians in east asia are adapted to and able to combat Db; but, amphibian populations outside of the region are more susceptible to it. (Scheele et al., 2016). Since the 1950s Db has become widely spread by humans due to enterprises like the pet trade, and has swept across every continent (Scheele et al., 2016). Since the early 2000’s, it has caused the decline of more than 500 species and the extinction of at least 90 species worldwide (Fisher & Garner, 2020). It is one of the most biodiversity-impacting pathogens we have ever seen. Our goal as a research team was to find out where Db existed locally, and how the canyon tree frog populations had been impacted by the combination of disease and drought. 

The research soon took some interesting turns, the genetic testing revealed that while Db was often present, it was at low levels. Suggesting that the canyon tree frogs show a resistance to Db. Dr Walker started carrying an infrared thermometer, because he suspected that something about the high temperatures of the desert canyons kept the Db at bay. The data indicates that the tree frogs do well in the heat, often recorded at temperatures in the high nineties and, in one recording, 104 degrees. An astonishing temperature to find an amphibian, which are so sensitive to changes. After putting the data together, Walker eventually found that populations of canyon tree frogs were minimally affected by Chytrid. 

“The frogs get so hot in the summer that they probably kill it right in their own skin.” Said Dr. Walker “Finding that the frogs around Zion had chytrid in a lot of the canyons, but their populations really seem to be tied to rainfall or snowfall, not whether or not they had chytrid, was very surprising.” “So really they just need more rain…” 

Once, I asked him what his research had taught him about drought. Walker said “ it affects things that you don't expect… there’s a whole bunch of ecosystems that you don't even think about that are terribly affected.” “Who knew there were frogs in the desert in the first place, and now, they’re just not there anymore.”

Canyon tree frogs can only live in canyons with water, and in the two years prior, Utah experienced the driest 18 months in recorded history (Mankin et.al., 2021). 

In the last 4 years of research, Walker saw local canyon tree frog populations collapse alongside the disappearance of the streams that used to run reliably throughout Washington County, Utah. Some populations even seem to have disappeared completely. So we set out to see how much the historic drought has affected the tree frog populations that Walker had come to know so well. However, the landscapes of southern Utah, and especially the slot canyons, are dramatic. Going out to where the canyon tree frogs reside is no small task. 

We arrived at the meeting point with our standard gear, 3 ropes, harnesses and helmets, snacks, water, and 2 waterproof buckets full of swabs, gloves, thermometers, and test tubes. I drank as much water as I could out of my gallon jug, decided my 2 quart canteen would be enough and we set out. We walked about a mile through fragrant juniper and pine, over the hill and down into the sandstone valley. There was not a cloud in the sky, and the early morning temperature was perfect, but clearly rising quickly. Eventually, we came to a massive sloping cliff face on the edge of the swirling, red, pink, and white sandstone of Hidden Star Canyon. The view was stunning and my spirits lifted dramatically. I suddenly found myself eager for today’s canyoneering venture.

Canyoneering is the art of navigating down and through a canyon using ropes and some ingenuity. It lies at the crossroads of hiking, rock climbing, and puzzle solving. Many canyons can be miles long and require hundreds of feet of rope. Common problems that canyoneers learn to deal with include deep water, exposure to the elements, and many types of dangerous rock formations. The only way we were going to be able to collect our data on canyon tree frogs was canyoneering through some of the most beautiful rock formations in the country.

 I quickly found out that the first task of the day would be setting up a deadman anchor, which is a lot of work. So my spirits settled back down pretty quickly.

One of the most important techniques in the canyoneer’s repertoire is rappelling (known as abseiling outside of the U.S.). In its simplest form, it is using a mechanism to descend a rope in a controlled manner. To set up a rappel, the rope must be connected to an anchor at the top in some way. Anchors often come in the form of bolts placed directly in the rock, or petons pounded between the cracks, but canyoneers are usually a respectful and thrifty bunch, so trees, boulders, and even people are sometitmes used as anchors instead of drilling into the rock. The deadman anchor is one of my least favorite types, but is a necessity in the desert where trees are sometimes few and far between. A deadman anchor is a piece of webbing or rope wrapped around a boulder or or large solid chunk of wood (or dead human in more extreme situations), and then buried to create extra stability. The problem with canyoneering in the sandstone of Southern Utah, however, is that it is so smooth it does not accumulate much soil, so the only thing to bury a deadman anchor under is more rocks, the closest of which were not nearby.

So I set out gathering big heavy rocks. Carrying a 70 lb rock 50 feet across variable terrain on the side of a sloping cliff face is a bit stressful, and even more so the second time. After about 10 minutes of moving rocks the anchor finally felt secure enough that we were confident we weren’t going to plummet to our deaths during the rappel. Then, for redundancy in safety, we used an extra length of rope to tie a backup line to a tree uphill.

Dr Walker gave us his car keys and said “in case I die, you’ll need these.” He then clipped into the rope and started working his way down. We waited at the top for what seemed like an eternity, but never saw the anchor move an inch. When we heard a trademark hoot and a holler from the Canyon Cat (Walker’s canyon name) and we knew he had made it. 

I went next. I slipped my gloves on, clipped my figure 8 device and carabiner into the rope and started working down the slope until the cliff became vertical and all my weight was on the deadman anchor. It felt solid. I was relieved. I started down the water pocket in the rock. It was about 40-50 feet deep by 8-12 feet wide and there was a pool at the bottom in the deepest part. The weather was hot by now and I would have loved a dip but this water was full of life (like mosquito larvae) so I decided to avoid it. I slipped down to about a foot above the water so I could push off the wall and swing to the edge of the deep pool, a few feet away. Just as I was about to plant my feet I saw a canyon tree frog near where I was going to kick off from. The first one I had seen in 4 years. It just looked like a lump on the rock until I looked closely. It was the exact color of the white sandstone we were canyoneering in. It made no sound. I didn't have a bucket with the swabs in my backpack so I just let it be and stopped intruding. 

I walked over to the mouth of the pocket and looked down to discover that the rest of the rappel was a sheer cliff, then noticed the sprawling sandstone valley before me and was in awe. I finished the rappel, and we waited for the rest of the team. 

The temperature was now near 100 and the steep canyon walls provided no shade. We did our second and third rappells and spotted and swabbed about eight frogs along the way and ended up at the mouth of a very thin slot canyon. We squeezed through a few pockets which got slightly bigger the deeper we went, and when we got to the main pocket, about 10 feet across with sand banks on either side, we were rewarded with the sight of about five canyon tree frogs, the most we had seen at one site up to that point. 

Three years before, in 2019, Dr. Walker had done the same canyon with a different research group and they found more than 40 frogs. But numbers have been dwindling year by year, due to historic drought. Now we were excited to see a total of 13. 

The drought in 2020-2021 was the driest 18 month period ever recorded for Utah (Mankin et.al., 2021). The lack of precipitation, plus higher temperatures increasing evaporation, reduces amounts of surface water and runoff, as well as decreasing soil moisture, and thus the duration of water availability, or hydroperiod.(Kohli, et. al. 2019). Many canyon tree frogs rely on ephemeral pools to lay their eggs each year, as constant water is rare in the desert biome. The drought that Southern Utah has seen in recent years has reduced the number and volume of ephemeral pools, and caused many once-reliable streams to run dry. Drying of pools causes stress hormones to be released in Canyon tree frog tadpoles, which may trigger the physiological cascade that leads to metamorphosis into a frog sooner, leading to undersized adults, which lay fewer eggs (Kohli et al., 2019). This is why frogs are sometimes known as “signpost species.” Their health, and density are good indicators of an ecosystem’s wellness. Canyon tree frogs have some mechanisms to help them hold on in drying canyons, but their numbers are dwindling. If we are not careful their situation may become dire. This saddened me throughout the research, but seeing them was always amazing and felt like such a treat. 

Once we gathered our data we regrouped and Walker announced to us that this is a keeper pothole. The only way out was up a 7-foot wall with a deep pool of very untrustworthy, and smelly water at the base. So we set to figuring out how we were going to get out without falling in the deep turbid pool. 

After a few minutes I found myself with my legs spread about as far as they would go on the small banks on either side of the pool, at the base of the wall. My co-researcher is using my leg as a step. She gets about halfway up the wall and I heave her up the rest of the way. All the while the water threatened to engulf us. She then wedged herself in the crack and set herself up as a meat anchor, running the rope through her carabiner and down to us to climb out with. 

On the other side of the wall was some much needed shade. I was exhausted by the pothole escape and finished my water. I realised this was not great news but decided not to say anything just yet, assuming the others were running low too. We did another rappel and hiked about a quarter mile further down the canyon without seeing any other frogs, or standing water for that matter. My mouth was dry, I had stopped sweating, dehydration was in full swing. Then it dawned on me that we just rapelled and hiked 500 feet down. Then Walker made the dreaded right turn, out of the canyon, straight up the rocky, exposed hillside.

The hill was steep and the loose rock made the climbing treacherous. The group was focused and silent. I found myself with some time to think and my thirst kept bringing me back to thoughts of water. Trends in desert ecosystems indicate that drought may be a long-time issue due to its relation to climate change (Mankin et.al., 2021). Amphibian populations are going to have to adapt or die while we learn to take care of our natural places. In the face of this enormous adversity, humanity is making slow progress and biodiversity across the planet is suffering for it. 

After quite a bit of complaining, and even some cursing, we made it up the hill. We retrieved our first rope and started hiking back. I was starting to imagine what water would feel like on my tongue. It was more than 100 degrees as we scrambled back up the petrified sand dunes, over the hill and to the electric blue toyota. There were cries of elation all around when we finally got there. 

We stumbled out of the bushes crusted with dust, some of us covered in pond scum, smelling like frogs, and more dehydrated than some people get in their whole lives, but we were satisfied. The work and suffering was worth it because we knew that our effort may help address the losses in amphibian diversity in the last 2 decades.  We spent one day with a lack of water. More and more amphibians in Southern Utah are spending their entire lives with lack of adequate water. Intense thirst is stressful and left me feeling connected to the canyon tree frogs in a way that I didn't expect. I mourned what was happening to them and felt helpless because I felt I couldn't do anything about it. The pain and fear of dehydration is not something I would wish on any creature, but as a society we are forcing it on an increasing number of organisms every year. Greenhouse gasses raise temperatures at surface level and cause the most severe vapor pressure deficit in 2000 years, which pulls water out of the soil and exacerbates the impact of drought (Lisonbee et al., 2022). 

The data, when we put it all together, was not good news. Populations had disappeared in some canyons and almost halved year after year in others. These trends may continue with global climate change, and the southwest ecosystem runs a risk of losing these frogs altogether (Lisonbee et al., 2022). We were left disheartened but not without hope.

The damage that has been caused by fossil fuels and climate change can be reversed, especially if our biggest polluters (big businesses) start to adopt serious ecologically friendly initiatives. Society has to send a message by buying ecologically friendly products and investing in companies that have a positive impact on the environment. If we take action quickly enough, one day frogs may overflow from the canyons once again. 


Behler, J. L., & King, F. W. (1979). National audubon society field guide to reptiles and amphibians: North america (national audubon society field guides) (Illustrated ed.). Knopf.

Fisher, M. C., & Garner, T. J. (2020). Chytrid fungi and global amphibian declines. Nature Reviews Microbiology, 18(6), 332–343. 

Kohli, A. K., Lindauer, A. L., Brannelly, L. A., Ohmer, M. B., Richards-Zawacki, C., Rollins-Smith, L., & Voyles, J. (2019). Disease and the drying pond: Examining possible links among drought, immune function, and disease development in amphibians. Physiological and Biochemical Zoology, 92(3), 339–348. 

Kupferberg, S. J., Moidu, H., Adams, A. J., Catenazzi, A., Grefsrud, M., Bobzien, S., Leidy, R., & Carlson, S. M. (2021). Seasonal drought and its effects on frog population dynamics and amphibian disease in intermittent streams. Ecohydrology, 15(5). 

Mankin, J. S., Simpson, I., Hoell, A., Fu, R., Lisonbee, J., Sheffield, A., & Barrie, D. (2021). NOAA Drought Task Force Report on the 2020–2021 Southwestern US Drought.

Lisonbee, J., Ossowski, E., Muth, M., Deheza, V., & Sheffield, A. (2022). Preparing for long-term drought and aridification. Bulletin of the American Meteorological Society, 103(3), E821–E827. 

Scheele, B. C., Hunter, D. A., Banks, S. C., Pierson, J. C., Skerratt, L. F., Webb, R., & Driscoll, D. A. (2016). High adult mortality in disease‐challenged frog populations increases vulnerability to drought. Journal of Animal Ecology, 85(6), 1453–1460. 

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