6

Finding the Frog That Sings Like a Bird

I stood with a group of colleagues and students at a small village at the base of Pu Hoat mountain in Vietnam. It was the monsoon season, a time when most biologists head out of the drenched forests, but we were about to venture in. Staring up at the sheer mountain face, surrounded by dense evergreen forest, we were about to begin our search for a tiny, mysterious, turquoise green frog. We knew we were looking for the proverbial needle in a haystack, a miniscule frog barely half an inch in body size—an almost transparent greenish frog against a backdrop of lush green vegetation, in the vast mountainous forests of Pu Hoat Nature Reserve in northwest Nghe An Province, Vietnam.

Our journey began about nine months earlier, and in a very different setting. Sitting in front of my computer in my office at the Australian Museum in Sydney, I opened an email from my colleague Vinh. Vinh had attached photos of frogs he’d seen on a recent field trip. I’d been working on the amphibians of Vietnam with Vinh and colleagues for years, and it’s always exciting to see photos of the frogs and salamanders that call the mountains of Vietnam home. I flicked through the photos of some spectacular but familiar frogs—tiny brown horned frogs calling from the leaf litter, chubby little tree frogs perched on leaves, and mottled cascade frogs with enormous toe pads clinging to waterfalls. And then, there was a photo of a frog I hadn’t seen before! A tiny, almost transparent turquoise frog with flashes of yellow along its side and curiously black soles on its feet. This frog was completely unfamiliar to me, and even more intriguing, I knew of no known frogs in the region that resembled this tiny gem.

It was that single photo that brought my colleagues and me to this far-flung montane village at the edge of the forest at the hottest and rainiest time of year. We were in search of a mystery frog. However, before we could even think about finding the frog, we had to get up and into the forest. In actuality, it wasn’t very far in terms of distance from the village where we stood to where we hoped we might find the frog. However, the forest was dense, the paths were muddy and tangled with vines and fallen vegetation, and the route up the mountain was extremely steep. One particular section (which I labeled in my GPS as a phrase that I shouldn’t share) was an almost vertical slippery slide of mud and leaf litter. Lacking agility, I fell face-first several times and had to scramble up most of the steepest sections on all fours. Despite the challenging terrain, we climbed up and up, pausing occasionally to catch our breath before slipping and sliding up the mountain. The farther away from signs of the village, the closer we hoped we were to the mystery frog.

After several hours of sliding up the mountain, we reached about 1500 m above sea level. As we hiked, the forest had become incredibly dense and the track less and less obvious until we lost the track and the way completely. We stopped and scouted around until we found a small, clear stream. We’d all run out of water by then, so we gratefully drank from the stream, then sat on nearby rocks and ate dry biscuits and sticky rice before hiking up to a larger stream. Huge, round boulders flanked this fast-flowing stream and lush vegetation filled every nook and cranny. It was here that we made base camp, some of us in hammocks with tarps overhead, others simply laying tarps under the shelter of a huge streamside boulder.

After a meal cooked on a campfire, we donned head lamps and headed out in search of frogs, as darkness, and rain, fell. One of my favorite things in the world is to hear the sounds of the forest erupt as it gets dark. Most frog species call only at night, and as the sun sets the calls of male frogs begin to fill the air. In a forest in which the frogs haven’t been scientifically studied, this is particularly exciting. Amongst the honks, creaks, and whistles of frogs that were familiar to me were some strange and unusual calls. Some of these were likely to be frogs that I’d just never heard myself, but others were likely frog species that were unknown to science. One might even be the tiny green frog we were so keen to find. These strange calls lured us out into the night.

Walking alongside the stream, we heard frogs calling intermittently from within boulders in the streambed and from up stream banks. Seeing the frogs responsible for these calls, however, proved a challenge. The calling frogs were easily spooked and stopped calling as we got near; even if we thought we knew where they were, they seemed impossible to find in the thick vegetation. Indeed, the vegetation around us was some of the most dense that I’d ever seen—perhaps no surprise as the forest was misty most of the day and night, perfect conditions for plants to cling to every surface.

After a few hours of searching, we’d found only a handful of frogs and recorded their unique calls. While we recorded important information on these frogs, we didn’t find the frog we were really after. We returned to camp in the early hours, by which time it had gotten rather cold. The cool temperatures were exacerbated by the fact that we were all completely saturated from our night hiking through wet vegetation and streams. The water from the persistent mist clung to our bedding— and us—making for a soggy night all around.

After drying out slightly, and a day scouting around our main camp for sites to survey at night, we ventured farther from our camp the following afternoon. We found a slow-flowing trickle of a stream, and as darkness fell, we set about recording the cricket-like calls of some unusually large leaf-litter frogs. Crouching in the dark, we held microphones toward the calling frogs, turned our lights off, and hoped that the frogs would continue calling. Each recording provides vital information on the identity of the frog, including whether the frogs are a species known or unknown to science.

Suddenly, we heard a strange bird-like twittering from a boggy area to the side of the stream. We rushed over to the source of the noise and there, right in front of me, perched on a leaf, was a tiny, shimmering, turquoise frog!

The call of this frog species was like nothing I’d ever heard before. Usually, a frog makes a repeated call (ribbit, ribbit, ribbit). Sometimes they will have a little more complex call (reeek-pip-pip). But the call of this frog species was bizarre. No two calls were the same; there was a mix of high-pitched chirps, whistles, and clicks. The overall effect was like being surrounded by dozens of tiny, excited, high-pitched birds.

I was in absolute heaven! For the next few hours I stayed in this little grotto of turquoise frogs, trying to get clear recordings of as many calling males as possible. Whilst walking around the site trying to spot the frogs, I came across two clutches of eggs, each attached firmly to the tips of leaves. Only in the wettest of forests can frogs risk laying eggs outside water, where they could dry out if the humidity dropped. The eggs resembled small clusters of pearls, clinging to the tips of leaves, causing the leaves to droop at the tips. Tadpoles of this species must face quite a shock as they break free from the eggs and then drop into the water below to continue their development.

We returned to camp elated, and for the next week we continued documenting the frogs of this mountain before returning to our more office-bound lives. From our fieldwork, and follow-up work in the lab, our team was able to describe these frogs formally as new to science, naming them Quang’s Tree Frog (Gracixalus quangi), in honor of our colleague. We also scientifically documented the call of this species, and in doing so realized that Quang’s Tree Frog had perhaps the most complex and variable frog call known. As a result, the tiny turquoise frog that lays its eggs on the tips of leaves has been coined loài ếch có tiếng kêu như tiếng chim hót, or the frog that sings like a bird.