IT'S A RAINY SPRING NIGHT in the Tully River Gorge, and I'm hunting frogs. Swatting ineffectually at a swarm of mosquitoes, I slowly wade up a tiny unnamed creek as it tumbles down from Queensland's Atherton Tablelands to the rushing river below.
In the highlands above me, the rich forests of Wooroonooran, Girringun, Daintree and Koombooloomba have been evolving in relative isolation since the break-up of Gondwana tens of millions of years ago. Now they are fortresses of biodiversity, protecting a host of unique fauna: tree kangaroos, cassowaries, quolls and bandicoots, as part of the vast Wet Tropics World Heritage Area.
But while the combined clout of the U.N. and the Australian Department of the Environment has preserved the unique birds and mammals of the Australian rainforests, it has done little for the frogs.
Systematically exterminated by a water-borne fungus known as chytridiomycota (or 'chytrid') that scoffs at national borders, park boundaries and conservation areas, the frogs and toads of the world's high altitude forests are disappearing.
Since 1980 up to eight species have gone extinct in Australia, with many more in peril around the world. According to a 2006 paper by J. Alan Pound et al. in the British journal Nature, some 73 species have died out in the forests of Central America alone. Declines and disappearances are occurring in Africa, Europe, and the Andes of South America, and reports of infection from New Zealand and across North America hint at a pathogen that has reached across the entire planet.
I should have been in class that week I spent hunting frogs, but I'd been lured from my ecology courses at James Cook University (JCU) by a PhD student named Jodi Rowley (see "Portrait", Cosmos 15, p9). I knew her from her Townsville JCU office, hunched over her computer in a freshly laundered T-shirt and the ubiquitous Queensland thongs.
Now, eyes twinkling and clad in well-worn dive boots and shredded Gore-Tex, she held a rain-soaked court on the stream bank. We field assistants scoured the vegetation, sneaking up on frogs and grabbing them with plastic-bag-encased hands. Rowley weighed each one, swabbed its belly, tied a tiny radio transmitter around its waist and told us to return it to its original location.
At first glance, only a backward mind chooses night-time to look for tiny amphibians in the convoluted foliage of a rain-drenched jungle. But frogs are more active at night, and their eyes shine in the beam of a headlamp. Despite having to distinguish the minute red gleam of pea-sized frog eyes from the jumbled reflections of raindrops, insect eyes, and mica crystals in the river rock, frogging at night is far more efficient than waiting for daylight to search for their diminutive bodies.
The next day, though, Rowley's beacons led us straight to each one, and an infrared thermometer gave us their temperature. Rowley asked the question why, even as chytrid destroys some species in a given stream with horrifying efficiency, it leaves others alone.
Her results were intriguing. When she compared the temperature of each frog's daytime refuge with the amount of fungus it carried, the difference between life and death was just a few degrees Celsius. The fungus begins to die above 30°C, and species that preferred the warm forest foliage were staying alive, while those just metres away in the cooler water were dying. "Even though they're in the same genus, they're the same size, and they inhabit exactly the same stream, they can experience totally different micro environments," Rowley says.
