Found by ear: three years to a new tree frog

The office of the city nature reserve reported this week that a survey team has found a tree frog never before described, in a stream valley 900 metres up in the northern hills. It is less than three centimetres long and golden brown on the back, and on a mossy stone it all but melts into the fallen leaves. The paper describing the new species has been published in a journal of animal taxonomy, and the frog now has a formal scientific name.

The discovery began with a recording that matched nothing. In the spring of three years ago the team set out 16 automatic recorders in the reserve to listen for frogs calling at night. The team member who compares the sound spectra noticed a short, clear "dit, dit" that kept turning up at four of the sites, only two or three notes at a time, and unlike any of the 23 frogs known locally and held in the archive.

From a sound to a species

• Recording: 16 sites through three breeding seasons, more than 9,000 hours in all.
• Comparison: 412 clips of calls that could not be classified, concentrated in two stream gullies.
• Search: 37 searches along the streams on nights after rain; the first calling male was found in May of the second year.
• Identification: body form, call and genetics together confirm a stable difference from its closest relative.

"When it calls it hides in cracks in the rock and under fern fronds, and it stops the moment a torch comes on. We often crouched for an hour and had only the sound," says the zoologist who leads the team. So far the frog has been found only in two gullies in the core zone of the reserve; the estimate is fewer than 500 adults in a range of less than two square kilometres.

In the 22 years since the reserve was set up its list of amphibians has grown to 24 species, and this is the first vertebrate new to science to be found here. The site is not open to visitors, the office says, and a patrol path planned for the upper reaches of the two gullies has been rerouted to avoid the pools where the frogs breed.

Next, the team leader says, the recording sites will be extended above 1,200 metres to find the upper limit of the frog's range, and its numbers will be monitored for five years running. "Guard a forest in earnest and it will always tell you something you did not know."