Romer’s Tree Frog

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By 1952, when British veteran John D. Romer found himself exploring them, they had been emptied of all munitions and had filled up with drowned leaves, moss and the staccato call of curious, fingertip-sized frogs. The frogs were tiny, barely 2.5 cm in length and bore suction cups upon their thin toes, giving them the bulbous quality often seen in tree frogs. Perhaps their most notable quality, however, was the faint, dark cross emblazoned upon the back of each frog’s brown skin. Romer recognised them as a new species, although he was unable to do a proper study at the time. And he would never get to. A year later, the roof of the Kamikaze caves collapsed, sealing the creatures inside. No trace of them could be found in the surrounding area, and so it was assumed that the entire colony, and the species itself, had been killed.

Thirty-two years passed by…

The city of Hong Kong continued to swell. As it spread outwards into the surrounding countryside, the Urban Council grew curious about the creatures that hid upon the undeveloped hills and islands surrounding them. They asked a group of naturalists to write a “Field Guide to the Amphibians and Reptiles of Hong Kong”. Among these was Michael Lau, a PhD student at the local university. Along with his colleagues, Lau had been intrigued by the tale of a creature which had lived upon a nearby island until it was supposedly wiped out by an act of fate. The Romer’s tree frog, as the species had come to be known.

The naturalists took to crawling through the rainy forests upon the island of Lamma. They sunk their hands into any muddy pool or half-drowned cave with clotted leaves that might conceal the creatures. In one such cave, Lau discovered a group of unusual tadpoles. Pressing further in, they found that it slowly filled with a sound like sharp fingers furiously drumming upon the stone walls. And there, in the darkness, they found Romer’s tree frog calling out to them.

The revelation that Romer’s tree frog had survived on Lamma spurred the naturalists to search for more survivors. They found colonies on the neighbouring islands of Lantau and Chep Lap Kok. Despite their name, the frogs were not climbers and instead seemed to favour low lying areas choked with damp vegetation, like the cave in which Romer had originally discovered them. They liked somewhere they could safely hide. The Romer’s tree frog had been rediscovered, but it was far from safe.

The urban sprawl of Hong Kong was pulling the surrounding countryside into it. This put the frogs into increasingly close and dangerous proximity to humans. Only a few years after they had been rediscovered, the Urban Council targeted the frog’s home on Chep Lap Kok for the construction of the Hong Kong international airport. The island was to be razed; its forests stripped and its safe, muddy pools dredged. The frogs there would be completely wiped out.

Despite the odds, the tiny frog species endures

The naturalists crossed an empty stream and began to climb. On this end of the island, at least, the vegetation was thick – much thicker than it had been when the humans had lived here. As they ascended, trees began to crowd above them and weeds grasped at their feet. Tall plants crouched in the shade, waving broad leaves at them as the wind scuttled through the undergrowth. At the top of the hill, they found the dead body of a village. Concrete buildings lay here and there, windows wide and empty, staring out at the sea. Rotting furniture spilled out of them, exposed to the wind. At the centre of everything, a filing cabinet lay on its back, drawers dragged off by scavengers.

There was no sound except the scraping of leaves. It felt damp even though all the water here had died years ago. Whatever was left now had curled up inside muddy sinks and tumbled-down, rusted-out refrigerators. It was here that they found the skeletons – lying at the bottom of the grim pools that had gathered inside drowned washing machines and discarded cooking pots. They were small and scattered. The bones would have been invisible if they weren’t so numerous. But the pair knew that if they’d reached in and gathered them up, they could have reconstructed the tiny population that had managed to hold out here after the end had come. Something roared mechanically through the tree canopy and plunged the village into momentary darkness.

The plane passed over and returned to Chep Lap Kok. This was one of a few villages that the airport had killed. Lau moved to inspect one of the numerous pots that had been scattered when the villagers left, and called out to his companion. Chris Banks was Conservation Manager at the Melbourne Zoo, in Australia, and he was fascinated by the story that this pot contained. Incredibly, it seemed that, once the humans had left, the Romer’s tree frog had taken to breeding in the rainwater that pooled inside these abandoned pots, the abandoned sinks and filing cabinets and refrigerators. And so, in the absence of people, the frogs had managed to survive upon Chep Lap Kok. For a time, at least.

The frogs are a delicate species: they require still, safe water to breed in. In their natural environment, this often takes the form of isolated pools formed by rainwater or otherwise cut off from external sources that might admit fish which eat their eggs. Once they have found a safe pool, males attempt to summon a mate by calling out on the warm rainy nights, from February through to September. Females lay 120 tiny eggs, each 1 mm across, surrounded by a 5mm layer of protective gel. They hatch after 3 or 4 days and spend a month as tadpoles eating algae before they are ready to find pools of their own.

Lau and his colleagues had attempted to move the frogs out of the Airport’s path upon Chep Lap Kok by transplanting as much of the population as they could to nearby sites, such as The Tai Po Kau Nature Reserve, the Tin Fu Tsai Forest and even the Hong Kong and Melbourne Zoos. Unfortunately, humans had released mosquitofish into the wild around Hong Kong to reduce mosquito populations. In their new environment, the frogs found themselves at the mercy of the invasive mosquitofish, and many died. In Melbourne, it was an invasion of ants which killed the frogs. Sometimes it was simply the rain. The frogs relied upon thick, wet vegetation to protect their nesting pools from excessive water run-off. So, Lau and his colleagues built specialised, artificial breeding pots for them. But many of these were invaded by larger frogs which simply ate the Romer’s tree frogs. Other times, for reasons they could not understand, even humans would find these pots and destroy them. And yet, despite the odds, the Romer’s tree frog endured. In the dark interior of Lamma island, and the dank undergrowth of Lantau, safe in their damp decaying cradles of leaves, the original populations survived. Some of the transplanted populations that Lau and his colleagues established also held out.

The attention it deserves

Now, Hong Kong has begun to pay attention to the tiny but indomitable species. Part of its habitat on Lantau has been granted protection from the encroaching city. Across the region, a huge fine is levied against anyone who hunts, collects or otherwise interferes with the creature and its native habitat. The species is also now listed as ‘Endangered’ on the IUCN Red List of Threatened Species. While this seems like a dire prediction, the fact that it is listed after three decades of extinction is a victory in itself.

The Romer’s tree frog is more secure now than it has been in decades, Lau reminded himself as he and Banks stared into a silent, artificial pool that humans had made for them only by accident. He tried to recall the moment he had first heard their trickling call deep in that cave on Lamma, but another plane surged overhead. This one came so low that it actually rattled the water, making the contents dance. While the village had been abandoned, the southern tip of the island had not been developed when the airport came. Perhaps it never would be. Perhaps all these remains would stay here in silence until long after the planes have stopped flying. And perhaps the colonies that he and his colleagues had established around the edges of the city (and beyond) would survive. After all, Lau thought – as the colossal aircraft slid onto the tarmac in the distance and the water within the saucepan that had once contained more than a hundred frog’s eggs ceased to move – how much space do we actually need?

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