Things that go croak in the night

(AUSTRALIA) Our nights are echoing to competing choruses of 'warks', 'uks', 'bonks' and other strange sounds. Philip Hammond goes in search of this amphibian orchestra

The streams are finally running again in Brisbane Forest Park and the wet weather is the trigger for the metropolitan area's rich diversity of frog life to make its presence known.

Green tree frogs are amplifying their calls in innumerable downpipes. Striped marsh frogs are broadcasting their "dripping tap" noise in countless back yards and one less-common resident, the giant barred frog, may be heard uttering a soft muffled "wark" sound while buried deep beneath forest leaf litter.

The man who can identify a frog for you is Greg Czechura, a senior Queensland Museum technician who is concerned about the urban sprawl and the "less diverse landscape we are creating for ourselves".

Australian naturalists have so far discovered 225 different frog species and southeast Queensland and northern NSW boast 50 of them.

Brisbane has more than half of the region's species, making it Australia's most biodiverse state capital.

In an extraordinary range of habitats ranging from high-altitude temperate rainforest to acid wallum heath wetland, the Brisbane area's frogs range in adult size from just 25mm to 115mm.

Czechura fondly recalls when Brisbane had many more swampy areas and low lying ground below the Wesley Private Hospital, near Coronation Drive, would become "a big corroboree ground" of multiple frog species after rain.

"For me, in the 1970s, one of the icons of summer in Brisbane was the frog sound," he says. "You could walk around the suburbs on a humid night and, anywhere, listen to graceful tree frogs calling out from people's gardens."

Even today, flooded depressions in wet weather are often more attractive as frog breeding sites than specially made garden frog ponds, he says.

Eight or nine different species can sometimes be found in such big puddles because the creatures favour the gently sloping gradients into the water.

"When the rains kick off, the boy frogs respond first, popping up from their sheltered sites and heading for the breeding areas," Czechura says.

Frogs have 40 different development stages and each process, from fertilised spawn to adult stage, is temperature dependent. Different species develop at different rates, with some developing into adults in a fortnight, he explains.

With this year's late rain, a phenomenon called "diapause" kicks into the breeding process.

"It's like the pause button on your CD player. When temperatures drop, they can hit a point where tadpoles will simply stop developing," he says.

"This is why people find they have green treefrog tadpoles and, five months later, they still have green treefrog tadpoles. It's arrested development, like the way kangaroos pause joey development in a drought."

10 of our wonderful frogs

1

TUSKED frog. This broad-shouldered frog has a pair of bony tusks jutting from its bottom jaw.

It also is distinctive in having a marbled black and white underside and bright red patches around its groin.

Look on the water for its white foamy mass of spawn, which develops into large, dark-grey tadpoles.

2

GREEN-thighed frog. This 40mm white-lipped little frog is considered rare or threatened.

It has a rich brown back, broad black line down the side of its head and is yellow with black spots underneath.

Patchily distributed, it has been known to mysteriously arrive in large numbers, then quickly disappear again.

3

STRIPED rocket frog. This sharp-snouted frog which grows to 50mm will beat bigger rivals in the leaping stakes.

It copes with forest, swamps, suburbs and pastures and is a ground dweller.

4

ORNATE burrowing frog. This roly poly, snub-nosed frog emerges to breed after the rain.

It grows to 45mm and has highly variable, often complex patterns on its back. It also lays a whitish, foamy mass of spawn on the water's surface.

5

EMERALD-spotted treefrog. Not to be confused with a cane toad, this common frog grows to 65mm and has whitish grey or brown rough skin, with darker mottling and green spots. Frogs have softer features and lack the defined bone ridges of the cane toad's head.

6

SPOTTED marsh frog. A little less common than the striped marsh frog, it grows to 45mm and is pale grey with dark blotches on its back. Females have a white underside, which is dusky yellow on males. Found in alluvial areas around Brisbane, this frog's call is a rapidly drilling, vibrating sound of harsh "uks".

7

GRACEFUL treefrog. Not all tree frogs are green. This one, which grows to 45mm, is green and yellow, with orange eyes, yellow lips and rich purple hues on its thighs. It's a common garden species.

8

SCARLET-sided pobblebonk. This rotund frog with a fabulous name grows to 75mm and is sometimes seen in large numbers on the road after rain.

It has distinctive red or reddish-yellow areas along its sides and upper arms, a bright-red groin and white-yellow underside.

These frogs cocoon themselves in soft, sandy soils.

The mating call, made by males when almost submerged, is a resonant "bonk" sound.

9

GREAT barred frog. These 80mm brown frogs have broad, flat heads and big, dark eyes.

They are found near forest streams, open forest and farm dams near forest. They bury themselves in leaf litter and make their "wark" call while still buried.

10

NAKED treefrog. Patchily distributed and usually found in Brisbane's western and southern suburbs, this 40mm frog is probably Australia's most widespread and numerous. Colour ranges from almost transparent white-grey to fawn and purple-brown, with two dark patches in the kidney areas of its back.

* Pictures courtesy of the Queensland Museum's excellent reference book Wildlife of Greater Brisbane (ISBN 07242 64477). The book is packed with colour photographs and descriptions of just about every creature which lives in the state's southeast. RRP $28.95.

Froggy facts

STRIPED marsh frogs, with their "dripping tap" call, have driven neighbours to backyard violence, says Vikki Nichols of Queensland's Restoring Australian Native Amphibians (RANA) frog group.

"Neighbours have poisoned ponds. They have been found creeping around in other people's yards, saying if they find the frogs, they'll kill them," she says.

IF YOU see a frog with five legs, don't drink the water, says Queensland Museum frog expert Greg Czechura. Heavy-metal contamination of streams and creeks can often be first seen by the appearance of frogs with extra legs. As well as being food for lots of other native animals, frogs are the "canaries down the mineshaft" when it comes to signalling serious environmental problems, including salination and pollution, he says.

SINCE 1978, six species of frogs have disappeared from Queensland and at least another eight species have seriously declined in numbers. But there are still 36 native frog species living in the greater Brisbane area.

CHYTRID fungus has been killing Queensland's frogs since the 1970s but the good news is that some populations appear to be making a comeback. Queensland Parks and Wildlife Service frog researcher Harry Hines says giant barred frogs are reappearing in the Conondale Ranges, the cascade tree frog has been downgraded from endangered to vulnerable and, at last, the Fleay's barred frog population seems to be increasing in some southeast Queensland mountain streams.

TREE frogs are among the many native animals which need safe shelter in tree hollows. Making ventilated shelters from lengths of plastic and concrete drainpipe and tying them to fences and on trees may offer them much needed cover.

LONE Pine Koala Sanctuary has helped the fight against the chytrid menace. The quarantined research facility at Fig Tree Pocket has successfully bred from spawn the great barred frog, with a view to breeding the endangered Fleay's barred frog.

HEAR the recorded sounds of some of our native frogs by logging on to RANA's excellent website at www.wildsuburbia.net.

THE Queensland Frog Society says so much work has been done in urban areas to drain swampy ground and get stormwater away to the rivers that "frogscaping" back yards is a good way of giving native frogs alternative homes. But, says the Queensland Parks and Wildlife Service's Rick Nattrass, to avoid the risk of spreading chytrid fungus and other frog diseases, don't introduce native frogs to your backyard frog pond. If you've designed it well, with shallows, cover vegetation and nearby lights where frogs can catch bugs and moths, native frogs will find your garden by themselves and set up home.

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