ZooNooz Article - march 2006

Colourful corroborees

Frog numbers world wide are declining and one colourful Australian is among them.

DARCY SHEDDEN reports.
Illustration Glenda Jones
Photograph David Hunter

'Critically Endangered' - these are words guaranteed to send a jolt through the heart of all animal lovers. Unfortunately, for herpetologists all over the world, these words are becoming everyday terminology. Each year, as numbers of reptiles and amphibians disappear from their natural environments, these scientists, as well as other concerned biologists and passionate reptile lovers, try desperately to discover the reasons why.

In Australia, the Southern Corroboree Frog has unfortunately become a member of this ill-fated group. Found only in the Kosciuszko National Park in NSW, its numbers have plummeted from the thousands recorded in the 1970s to only a few hundred frogs at the most recent count. Tragically, one of our most beautiful amphibians is also, according to the International Union for the Conservation of Nature, our 'most endangered'. It is in imminent danger of extinction.

Corroboree Frog

The tiny animal, only 30 millimetres long, is treasured by frog lovers all over the world for its spectacular colouring - a canary yellow back with black stripes made up of ridges of granulated skin. This is the same colourful pattern as is painted on the bodies of Aboriginal men during some of their celebratory corroborees - the perfect inspiration for this frog's truly Australian name. The belly is smooth with black, yellow and white markings and is kept filled with ants and other small insects. It's a frog that is rarely seen to hop and instead moves about by walking on the tips of its unwebbed toes.

Corroborree Frogs live in the sub-alpine areas above 1300 metres at Kosciuszko, hibernating under the snow during the winter months. During the warm months, the breeding adults congregate in moist sphagnum bogs and tussock areas near small pools. There, in the mossy vegetation, the male will dig a nest a few centimetres deep. Once completed, his harsh (but hopefully alluring) 'ark' call will begin, as he
attempts to entice as many females as possible to deposit their small clutch of eggs in his nest. Usually each female lays only between 12 and 30 eggs. After fertilisation, these eggs can hatch in as little as four weeks, but the tadpoles then remain in the nest in a moist jelly-like substance for up to seven months. Significant rainfall is required to wash them into the adjoining ponds before they can then begin to morph or change into adults. For an amphibian (most of which lay thousands of eggs directly into water), this is a most unusual and lengthy cycle of reproduction and, it appears, an extremely hazardous one, as it may be a major contributing factor to the frogs' drastic decline. Low rainfall at the critical time means the tadpoles are not flushed into the surrounding pools - effectively wiping out the entire year's population. The extended periods of drought, which have been experienced in the Park for quite a few years, have very likely decimated local frog numbers.

Habitat destruction by ski resort developments and trampling by humans and livestock may also have affected the Corroborree Frog to a small degree, but amphibian experts now feel that an important factor in the decline, (and many biologists feel it is actually the primary cause for the world-wide decline of many frog species) is the deadly, and highly contagious, Acute Amphibian Chytrid Fungus. (This disease may have been introduced into Australia in the 1960s, possibly with African Clawed Frogs imported for medical research.) Contracted during the tadpole stage, the chytrid fungus kills by destroying the skin of the adult frog. Ultimately, with no frogs of breeding age left, the species cannot survive, and our wild Corroboree Frog population has tested positive for the fungus.

Taronga has joined the battle to help preserve this precious Australian and, with the valued assistance and expertise of the Amphibian Research Centre in Victoria, has established a new exhibit here at the zoo - a purposebuilt room that is both totally climate controlled and completely quarantined from the outside world. This exhibit will display a small number of captive-bred adults, and will also allow visitors to view a hatchery area, where fertilised eggs are nurtured into tadpoles and frogs. Some of these will be released into their natural environment to increase numbers on the ground, while the remainder of the population will be retained for use in a captive breeding program.

In a 2003 interview with the ABC's Catalyst programme, Gerry Marantelli, head of the Amphibian Research Centre stated "...it is estimated that 25% of the world's frog population will be destroyed by chrytid. ...in Australia, eight frog species have disappeared in the last 20 years...without a doubt, the Corroboree Frog will go extinct in the wild." Captive management may be the Corroboree Frog's only hope of survival and Taronga hopes to play an important role in the recovery and survival of this 'jewel' of the amphibian world.

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