The Cave of Death is not much of a cave, so to speak, but it is a really fascinating hole in the ground nonetheless.  Extending only about 10 feet into the hillside, it ends at a crack too small to continue.  That is, if it were reasonable to continue for other reasons.

Located on the flank of the Poas Volcano in Costa Rica, the Cave of Death just happens to be near some very nice hot springs which have been developed into Recreo Verde.  This fine place was our base camp, actually a fabulous cabin, for our work in this area.

And as for the cave, it is a bit of a tourist attraction, and probably one of the few commercial caves where one does not in fact go in the cave.  Why?  Good question and glad you asked.  The reason for the name is fairly simple, as the cave itself is a huge emitter of nearly pure carbon dioxide.  This, as one might suspect, is what could mildly be called, "bad air" and it is quite dangerous and often fatal to animals that enter the cave.

But, since carbon dioxide is heavier than air, the "bad air" is mostly along the floor, and in fact pools up at the entrance with the spillover rolling out of the cave and along the ground.  How do we know this?  Another good question!  Guy van Rentergem invented a clever little smoker device out of an e-cigarette machine, which could be placed in specific spots to see exactly where the gases were going.  As well, we used a carbon dioxide meter to determine where the gas was and in what concentrations.

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Note that the signs in the photo helpfully say "toxic gas", "entry prohibited" and "don't throw trash".  The last one is kinda funny, compared to the others, until you realize that any trash thrown in the cave is rather hard to retrieve since you can't just go in there and pull it out.

And just to be thorough, we tracked the gas with smoke all the way out of the protective barrier at the cave's entrance where it eventually drifts off in the breeze, while staying right along the ground.
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And while Don McFarlane was taking a number of scientific measurements and recording data and just being an all around science guy...
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It still baffles me as to exactly what he was doing here...

Anyway, one of the more notable features of the cave is the pool of carbon dioxide on the floor, which is remarkably stable, and nearly 100% CO2.  It is just deep enough that any small animals that go in there, end up in that oxygen-free zone and quickly pass out and die.  The Recreo Verde folks told us that the most common animals that die in the cave are rats, snakes and small birds.  And, just looking in we could see at least one fairly recent fatality (sorry, I can't get a species from this photo).
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The smoke was really useful at showing the gas movement out of the cave, but what would it do when placed under the level of the carbon dioxide pool?  Man, you have all the great questions today!  Turns out that the gas has a very slow-moving eddy effect going on, and after a minute or two of watching the smoke it looked like a galaxy was forming.

And just for an added attraction here at Tropicalbats.com, a video about the cave from none other than Guy van Rentergem!  

So that is the Cave of Death, a carbon dioxide-emitting hole that has a penchant for killing small animals.  And now I know you have one more question:  Did any of us actually go in there?  I end with this photo...

***Huge thanks to Recreo Verde for allowing us to study their most interesting little cave.  Awesome place to stay on all accounts and really enjoyed it there.

Playa Ventanas is a nice little tourist beach in southwestern Costa Rica on the Pacific side.  It boasts a large expanse of sandy beach and while not entirely safe it is more suitable to swimming than in some places where the currents can really be dangerous.

We stopped by as there is a fairly well-known sea cave there and wanted to check it out.  But of course, we stopped and sat in the shade for a bit like normal folks do just to enjoy the place a bit.

One doesn't have to go far to find the cave, as it is pretty much just to the left of where I was standing when I took the beach photo above.  Easy peasy!  

​And this is what you see looking at the highwall.

The hole on the left seems to be connected to the larger entrance on the right so probably all just the same cave.  But why not just go in and find out?  What kind of cave explorers are we anyway?
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So looking into the larger opening you find that you can see right through the hill and out to the ocean.  Pretty long cave, so surely Don will explore it and map it and study it until it gives up all its secrets.

It should be noted here that Don is in the cave.  Technically anyway.  But where is his hard hat and light?  And gear?  Seems a bit timid about things.

And like Sir Robin in Monty Python and the Holy Grail, He bravely ran away.

So what is going on here?  Why am I asking so many questions?  For an answer, here is a short video of the inside of the cave:

So, as can be seen the inside of the cave was less than tourist friendly.  We were there too close to high tide to go in there, although I understand that things are quite a bit more calm at low tide, and we plan to return with better timing at some point.  Anyway, there was no need for caving gear as it was clear from the start that we wouldn't be going in there.

So we hiked down the beach to the other rocky area to see if there were any more caves nearby.

We didn't find anything else enterable, but at the rocky point where the high tide prevented further shoreline exploration, Don hung out for a while.  It was, overall, a pretty nice place to do so.

And finally, for those who like their photos a little Outside Magazine-ish, I goaded him into posing a shot.  After this bit we headed on down the road.

After our visit to Campanario, we headed back to the Firestone Center in Baru, Costa Rica.  The route took us by the sea cave where we had previously done some work, so decided to give it a bit more attention, with installation of the ammonia sampler as well.  We only had to go into the chamber with the big bat colony once for this, so figured it would add a lot of data to our bat cave work without much bat disturbance and could just use red headlamp lights for the roost work.

First up is Guy with his contraption for automatic sampling of ammonia over the course of a programmable time frame.  This thing worked flawlessly in what can be called less than ideal conditions.

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We also did more carbon dioxide sampling at various places in the cave.  

And finally, the airflow.  It is one thing to have a set of numbers placed on a surveyed map which show things at this point or that point, but it is even better to have those numbers with an idea of why they are what they are.  By using smoke from a vaping machine that Guy created we could essentially map the airflow patterns and speed without introducing anything harmful to the cave environment.  

And, well, that is going to have to be all for now.  I will finish blogging this trip after I return home as while it has been difficult at times to do so from here, after tonight it is impossible to add more.  But we have been to some pretty interesting places, and still have two days to go, so look for a continuation of posts in a couple days to catch up on the final bits from the trip.

So for our last night at Campanario, Guy and I decided to just head over to the spot above the cave with the benches and watch the bat flight.  This is just a really nice way to have a great wildlife experience while the sun goes down and darkness arrives.  Birds stop calling and frogs start up.  Day insects find a hidey hole and the night insects come out.  And the bats wake up and fly out of the cave.

Okay, I gotta say here that "bats wake up" is a bit of a mystery to me.  I have been in hundreds of tropical bat caves and at any point, with lights out and even before they know I'm nearby, they always seem to be awake.  Cave bat colonies are never quiet and sometime really quite loud.  You can turn your light off and sneak up on them from a long ways off with a dim red light and still hear them making a racket three turns of the cave passage before you get there.  Makes me wonder if the bats ever actually sleep.

Okay, back to the cave.  Earlier, we had seen a black hawk sitting on a downed tree with bats flying by trying to score a late evening snack.  I never got a photo of it going after a bat but it clearly wanted one.

So as it was getting pretty dark, with just a hint of yellow-orange in the clouds out on the ocean horizon, I took one last Campanario Bat Cave Photo.  I end this set of blog posts with a Pteronotus flying out from the cave and passing between me and the ocean.  A flash went off in the night, and Guy and I headed back to the Station.

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The owner of the Campanario Biological Station, Nancy Aitken, decided that since we had the cave entrance rigged it would be an opportunity for her to check on her bats personally.  Nancy is amazing in a lot of ways, truly one of the best of the best, but most of her visits to the cave are for taking students and other visitors to the station to see the bat flight in the evening from benches above the entrance, not going down to the cave.

The cave itself is, for the most part, a place very few should visit.  The wildlife watching opportunity outside the entrance, is something not to be missed.  The cave is obviously an important breeding site for Pteronotus in Costa Rica, and for the most part they will continue to do just fine without anyone entering the cave.  While watching the bat flight is really fun and doesn't bother the bats at all.  It's a win-win.

So we went out one afternoon at low tide, and after finishing up with our work and pulling out Guy's ammonia sampler, Nancy got to check on her bats.  Now I am not going to tell you her age, but let's just say most with that many candles on their cake would not be dropping down a rope to visit a hot, stinky cave with the surf pounding away on the rocks just a few feet away.  Actually most anyone, of any age, race, gender, country of origin, or shoe size would not visit this place voluntarily.  But here is Nancy climbing out after getting a look at the cave and the bats.  Truly remarkable lady in every way.

And, just really want to thank Nancy here for all her wonderful hospitality.  She made this part of our trip work super smoothly and was just wonderful to hang out with and hear her stories.  Hope to return and spend more time out there at some point as Campanario was a real treat to visit.

At the end of the cave one comes to a climb of maybe 8 feet.  This looks climbable, although not super easy.  But we ran into what might more be called a biological obstacle.  The entire climb was covered with a mountain of baby bats.  Lots and lots of baby bats.  

I was the first one into the cave when we got here so as to be able to assess what was going on with the bats.  There is a kinda low-ish spot right before the final room where you then stand up and are almost eye to eye with a whole lot of bat pups.  Odd the pups were down this low instead of on the ceiling, but...  It certainly was hot enough even down that low.  We took a temperature reading on the ceiling where the huge colony of adults was and it was a stunning 99.7 degrees F.  

There are three known species of bats in the cave, all in the genus Pteronotus.  I may be able to tell which species this pup mountain consists of, but that will wait until I get home and can work out the structures that separate them using the macro photos as I didn't handle any bats as that wasn't our purpose here.

Oh, macro photos?  Let's take a look at the bats from just a little closer.

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And just to show how absolutely adorable baby bats are, let's get right in close

Okay, just one quick image of the ceiling roost as well.  Of note, that is almost all I've got in the way of such images.  In a cave that hot, with humidity almost certainly 100%, camera lenses fog up very fast.  Plus their is a rather unpleasant rain in the cave, that is the rain created as all those bats are peeing and pooping and you are in between it and the floor.  Suffice it to say that when I went in to specifically photograph the whole colony, which takes three photos, I came out absolutely covered in, well, unpleasant stuff.  But also so was my camera and camera lens and flash covered.  Spent quite a while cleaning things later but still had to abandon one lens filter as it won't be clean enough to use again until after I get home.

So here is one of the shots looking up before everything was covered in fog and bat droppings.  

One of the primary reasons we were interested in this cave was to sample the ammonia levels under what is one of the larger colonies of cave bats in Costa Rica.  To do this required Guy to build essentially from scratch a tripod-mounted sampler that had five chambers that opened and closed at a programmable interval.  Got that?  

So what happens is that each of the five tubes near the top is spring-loaded, and you push one down and load an ammonia absorber into it.  Then you do that for the other four.  Guy previously hooked this up to his laptop and programmed in for the thing to work so that each tube was open for a couple hours before closing again, giving five samples over the course of a day.  Also key was that at that point we had to go and change the absorbers and it would hopefully be low tide.  The tide charts were consulted and Guy programmed his contraption to be timed with the tides as well.

So off we went at low tide, which was of course quite late at night when all the good people of the world should have been asleep.  At the cave entrance Guy got the thing out and ready to go.

Next was to lower it to the bottom and get it inside before a wave could come crashing in and soak it.

And finally, Guy installed it in the cave and checked things over and all was good I in the world.

For all intents and purposes, this was as far into the cave as we could go.  The climb right behind Guy was un-climbable, but we could actually see the end of the cave from there once we got a stepladder into the cave later.  Wait...climb was un-climbable...you had a stepladder in the cave...and...didn't use the ladder to do the climb???

All true.  It wasn't unclimbable due to the structure of the cave or it being too high.  Depending on which direction you are reading my blog you either know why, or the next post will answer exactly that question.

The first thing we did upon arrival at Campanario was to take a walk to the bat cave and rig a rope for access.  It's a sea cave so we really weren't sure how easy (or not) it would be to get in there.

At the entrance Guy rigged a rope that could be used either for rappelling or as a handline depending on how difficult it would be.  Sometimes rocks can be quite slippery, and nice to have the rappel option.  Don gave it a quick try and found that it worked okay as a handling as things weren't slick and there were a few foothold in there.

The other key factor here would be how much water comes in when a big wave hits.  It was mid-tide and so generally dry, but we quickly learned that it would be best to plan on getting wet.

From this little bit, we decided to mostly try and time our visits to the cave around low tide.  

We have just returned from Campanario Biological Station in southwestern Costa Rica.  One extremely nice place to stay and study things run by the most amazing Nancy Aitken.  I want to thank Nancy right up front for all the hospitality and help with our bat cave work and making the whole trip work out so well.  And as a side note, the food is so good there that as a caver one might start to worry about adding a few pounds and not fitting through everything they used to if you stay too long.

I can't write a whole description of the place, but you may visit their website to learn more about this field station

https://www.campanario.org/

We took a boat out of Sierpe, down through the mangroves along the river, and out into the Pacific ocean.  Bit of rough water right where the river meets the sea, but our boat captain circled until he saw a gap in the wave pattern and got us through with minimal bashing about.  Kudos to him, as he really knows how to read the water.

At Campanario it is a wet landing, as in there is no dock they just back the boat up to the black sand beach and you jump out.

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Mostly all this is stuff chucked on your shoulder or hand carried to dry ground.  For some reason Don seems to have thought this was a luxury tourist resort and, well, ended up trawling his wheeled luggage across the sand.

The Station itself I can not do justice to in a photo.  It maintains a small footprint with maximum usefulness, so pretty unassuming when seen from the beach.  But oh yeah, they've got it all worked out very nicely and working here was super easy.  And did I mention that the food was amazing?  

And it didn't take long to see some wildlife.  This red-tailed squirrel was bopping around in the trees beside the Station and cute as can be.  Things were now in place to spend a couple days figuring out the nearby bat cave and hiking some trails to see some wildlife.

My internet has been pretty iffy but that squirrel photo looks great in my files but terrible here to me.  I'll check and upload it again later.

Don McFarlane, who honestly owns and wears a kilt at times, organized this bit of madness to Costa Rica.  We are looking at a number of relatively small caves with relatively high levels of bat populations, bad air and bad chemistry.  For a renowned caver I must say this is one of his more hairbrained ideas.  Yet here I am and looking forward to every bit of it.

Today's mission was to a cave in southwestern Costa Rica, a sea cave, with a bat population of around 800 individuals of three species (all in the Pteronotus genus).  There just aren't all that many caves here, so the bats that need caves can really pile into even a small cave that fits their needs.

While we have visited this cave before, this time was mostly just to retrieve a data logger that was placed in the bat roost.  No big deal, just go in, get slopped in the guano muck, and get out with the tiny bit of electronics that has been recording atmospheric data for many months.

However...this time the tide was several feet lower than we have ever seen it, and we were able to walk down a beach that was previously pounding waves on a sheer cliff face.  To our surprise and good luck, there were more caves.

One was a tunnel that cuts through the rock somewhat parallel to the beach.  Beautiful, but not too exiting for bats or other cave stuff.

Another of the caves had the usual joint-controlled main passage going in straight from the shore, but there was a little bit of apparently phreatic passage going off on both the strike and the dip of the rock (the dip passage is behind Don and not visible)

After hiking the beach that wasn't there last time we visited, we finally went back and retrieved the data logger in the bat cave.  And, for one more bit of science Don mapped the carbon dioxide levels in the cave from the entrance to the bat roost.  As expected, CO2 was much higher at the roost.

Probably a bit about this photo is needed here as well.  This is Don, holding a CO2 sniffer, below the bat roost.  And while it looks like it is snowing, that's not exactly the case here.  All those white spots are either fungal gnats or Tineidae moths (no way I can really tell).  Fine, but they are attracted to light so a caving headlamp essentially is a great way to attract them into your eyes or up your nose.  Such fun.

Otherwise, there were numerous giant cockroaches on the floor and it was raining in the cave.  No, not water rain, but just think about standing under 800 small mammals and you get the idea of what was raining down.

And...looking up from where don was standing I took a quick snapshot.  The bats are just carpeting the top of the fissure.