Forests and Flying Frogs: Surprise Sinkholes

Jodi Rowley is a National Geographic grantee discovering and documenting the diversity, ecology and conservation status of highly threatened amphibians in the forested mountains of Vietnam


I wake up with large, knobbly tree-roots digging into my back. Our basecamp in the forest has been leaning over more and more each night. It’s now reached the point that it will literally collapse in on us if we actually lie in our hammocks. None of our attempted fixes have worked. So, last night we simply lay on the ground, with only a thin layer of plastic between us and the forest floor. We still got into our hammocks, tying the ends to the wooden frame just enough so that the built-in mosquito nets kept off our faces. I’m very glad that the night is now over and I can get up off the ground!

After a breakfast of instant hot-chocolate, I take photos of the amphibians we found last night, including the tadpoles. I’ve brought little glass aquaria with me, and put tadpoles in, one by one, and try and make them lie still, perpendicular to the side of the aquarium. Not surprisingly, they prefer to keep moving as fast as possible around the aquarium, burrowing into the gravel on the bottom!

After I’ve given up on the last few tadpoles, four of us sit together and record as much information as possible about the amphibians we found the night before. It’s a routine that we’re all familiar with, as we’ve worked together before (a couple of us have spent months surveying amphibians together in the forest). We carefully examine and weigh each frog, take detailed notes and photos of frog eyes and thighs (see my previous post) and chat.

In the afternoon, we don our muddy clothes and set out for the forest over the ridge. Almost every time we venture far from camp small sink-holes camouflaged by vegetation get least one of us (which is always amusing as long as no-one’s hurt!)

Vegetation masks the absence of solid ground. Thankfully, all falls into holes were funny (no-one was injured). Photo by Jodi Rowley
Vegetation masks the absence of solid ground. Thankfully, all falls into holes were funny (no-one was injured). Photo by Jodi Rowley

As the sun begins to set behind the mountain peaks, we cross a couple of large, rocky streams and reach a well-worn path. By now, it’s dark, but it’s obvious from the huge hoof prints and occasional cow-pat that this path is frequented by cattle.

Although no biologist has surveyed this forest before, there’s far more signs of humans here than perhaps anywhere else I’ve ever surveyed. I expected this, as it’s not a protected forest, we’re not that far from a village, and there’s another village on the other side of the forest. What is unexpected to me is how a large cow with seemingly clumsy hoofs can climb up such a steep, rocky, narrow trail. I think I’ve been underestimating cows all these years.

We follow the cattle-trail up the side of the hill for about 15 minutes, reaching a grassy clearing at the top. The sky is clear and the moon is full, casting light on the hilltop and the valleys below. The jagged peaks around us look magical in the moonlight, and we turn our head-lamps off and sit together in silence. It’s a truly memorable moment….until the local guys realise that we have mobile phone reception up here, and start calling their friends, filling the silence with chatter and ring-tones.

Once mobile phones are put away, we hike across the clearing and descend into the forested valley below, following a wide, rocky stream until it turns into just a trickle of water running through tree roots. The forest is much less disturbed here, with no signs of humans or cattle.

I’m happy to be in good forest, although it is more difficult to walk. We have to crawl under and over logs and push through vines and tree branches to make progress. All the while, we scan our surroundings, searching for the pale red glow of frog-eyes in our head-lamp beams.

Limestone terrain, northern Vietnam. Photo by Chad Minshew
Limestone terrain, northern Vietnam. Photo by Chad Minshew

Bit by bit, the terrain gets rougher. First, it’s just a couple pointy limestone hills about the size of a small car that we have to climb over. These patches are separated by solid ground that we can walk upright on. But then we begin traversing some of the most dangerous, potentially-laceration-causing limestone rocks that I’ve ever encountered.

The picturesque jagged limestone is covered in lush vegetation and thick moss, reminding me of the beautiful terraria you see at zoos. It looks lovely, but when you’re in the middle of it, it certainly isn’t! The vegetation clinging to the rocks makes it hard to see what is rock and what is a human-sized pit. The rocks are pointy and sometimes snap off when we hold them, cutting our hands, and they’re surrounded by sink-holes and chasms.

We crawl slowly over the limestone, being as careful as we possibly can. I really don’t know how, but after about 15 minutes we all make it back onto solid, less pointy ground with only a few grazes. I think I just worked out why the forest around here is undisturbed. No-one in their right mind would go through that terrain intentionally!

While the treacherous limestone revealed just a single small brownish-grey Leaf-litter Frog with skin almost as bumpy as the rocks around it, elsewhere in the forest, we spotted some amazing amphibians. Most of them were tree frogs, and they spanned the entire size-spectrum.

Tiny brown Bubble-nest Frogs the size of a dime called loudly from bright green leaves throughout the forest. Medium-sized tree frogs with mottled green and grey skin were everywhere- every few minutes I spotted one perched on a tree branch, white belly shining in my torch beam.

Feae's Tree Frog (Rhacophorus feae) is the world's biggest tree frog. Photo by Jodi Rowley
Feae’s Tree Frog (Rhacophorus feae) is the world’s biggest tree frog. Photo by Jodi Rowley

Skinny, pale-brown tree frogs frequented the vines and branches near streams. However, the most exciting frog to see was the biggest species of tree frog in the world, Feae’s Tree Frog. This enormous, regal frog was surprisingly abundant, just hanging out up trees in the forest, occasionally calling to each other in a deep, croaky grooooowwwwl.

Another treat was seeing a stunning species of lizard- males had “lips” emblazoned with bright orangey-red “lipstick”.

Once back at camp, I wash up in the stream and brush my teeth, ready for another night sleeping on tree roots. As I try and get comfortable, I think of all my friends back home sleeping on plush mattresses.

Read the entire blog series


, , , , ,

Meet the Author
Jodi Rowley is a National Geographic grantee discovering and documenting the diversity, ecology and conservation status of amphibians in Southeast Asia. Amphibians in the region are both highly threatened and poorly known, and Jodi and her colleagues conduct scientific expeditions to the forested mountains of Vietnam in search of amphibians.