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Tadpoles on the hop
Across Australia, tadpoles are changing. They're growing legs and becoming frogs - one of the miracles of nature that has enthralled children for generations. The beginning of autumn is peak time for witnessing this amazing metamorphosis - but there's a sting in the tail. Frog numbers have been fast declining around Australia for a number of years.
Camouflage 
Watching Breeding Frog kill Urban frog-pond Green and Golden Bell Frog Get involved
The smart tadpole is the one you can't see!
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Despite an abundance of tadpoles following the summer breeding season, they're not as easy to find as you might think. Most tadpoles hide from predators in the mud at the bottom of a pond or creek, and only come to the surface to stock up on air.
The metamorphosis from tadpole to frog usually occurs two or three months after the tadpoles hatch from their egg, however, like everything else about frog reproduction in Australia, the time it takes varies widely.
Two factors appear to trigger metamorphosis:
A simple rise in temperature can trigger the change in many species.
2. A lack of food can also be a major motivator. As the tadpole's food supply runs out, changing into a frog provides access to more food from its environment.
The change from tadpole to frog can be held over for many months if conditions aren't right. Although the typical time frame is around six weeks to three months, some desert frog species take as little as 16 days while one species of Barred Frog (Mixophyes spp.) can take as much as two years to go all the way from egg to frog.
Fact file:
When: When the conditions are right. While most frogs breed in late Spring and early Summer, you'll still get a few doing their thing in March. However, there are no hard and fast rules when it comes to Australian frog breeding season.
Where: Australia wide
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Hear frogs croaking in a pond near Sydney(Duration 20 "). The long drawn out croak is the Green and Golden Bell Frog [listen (requires real audio)].
Watch it if you want - it's legal!
There's an easy way to watch the process of metamorphosis - the change from tadpole to fully-fledged frog. It's as simple as taking a large glass jar down to the creek and catching a few of the frog eggs or tadpoles you find.
Want to collect tadpoles? |
Although frogs are protected across Australia, there are provisions that allow you to capture tadpoles, watch them change into frogs, and then return the juvenile frogs to the place you captured them.
It's a golden opportunity to watch a small miracle of nature in action. Just remember to give the tadpoles plenty of clean, fresh water (rainwater is best) and some food (a bit of boiled spinach or lettuce) and the amazing change from tadpole to frog will take place before your eyes.
Any season is breeding season
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While most frogs breed in late Spring and early Summer, you'll still get a few doing their thing in March. However, there are no hard and fast rules when it comes to Australian frog breeding season.
Aussie frogs tend to be highly opportunistic breeders - they lay their eggs when the conditions are just right. So the time of breeding and metamorphosis varies widely from year to year due to the irregularity of rain across the country. Combined with the fact that different species prefer to breed at different times of the year, this means you can find frog eggs and tadpoles almost all the year round if you look hard enough.
The number of eggs a female frog can lay at one go also varies enormously around the country. Some desert frogs produce an astoundingly low 10 or 20 eggs a year while the Green and Golden Bell Frog (Litoria aurea) can produce around 10,000 eggs at a time.
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Australian native frogs typically produce 1,000 to 2,000 eggs a year but when it comes to the fearful imported Cane Toad (Bufo marinus), a single female can lay as many as 30,000 eggs in one sitting.
The great frog kill
During the 1980s reports of large numbers of dead frogs began to surface all over Australia. But it took until 1995 before a cause was found. It was a microfungal disease called Chytrid that had most likely been brought to Australia by somebody importing freshwater fish.
Chytrid is highly contagious and the tragedy is that infected frogs can't be identified until they are almost dead. Of the 240 species of frog in Australia, about 70 have so far been diagnosed as carrying this disease.
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Dr Arthur White, president of the New South Wales Frog And Tadpole Study Group (FATS) and a research associate at the Australian Museum, said the disease has been detected in all States, except Tasmania, and it appears it also hasn't popped up in the Kimberley yet. "The good news is that we now have some populations of Green and Golden Bell Frogs which are showing signs of resistance to the disease," Dr White said
The Frog And Tadpole Study Group (FATS) has been trying to find ways to cure frogs with chytrid and they've had some success. James Cook University in Townsville also has a major research program underway into chytrid disease and the Animal Health Laboratory at Geelong is developing a diagnostic kit to identify frogs that are infected with the disease.
An urban frogpond
The Green and Golden Bell Frog (Litoria aurea) became famous when it was found at the site of Olympic Park at Homebush and became a mascot of the environment during the 2000 Olympics.
The Green and Gold Bell Frog is now and endangered species, so the Frog And Tadpole Study Group set up an experimental pond in the Sydney Suburb of Marrickville to see if it could be reintroduced into urban environments.
However, despite the erection of frog exclusion fences to prevent infected frogs getting into the pond, something went wrong. "After two successful years, a diseased frog jumped the fence and all but one of our frogs died from chytrid disease in the space of about five weeks," Dr White said.
Dr Arthur White describes the different sounds frogs make (Duration 35") [listen (requires real audio)].
Just add salt!
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Dr White and his team then experimented further with the pond and found they could kill the chytrid fungal spores with no ill effects on the Green and Golden Bell Frogs, or their tadpoles or eggs, simply by making the water slightly saline.
"Now I'm pleased to say we've got little frogs bounding around at the moment at Marrickville," Dr White said. "So we may have the beginnings of some sort of a management tool to protect tadpoles and possibly young frogs. We may have to think about salt sprays as a further extension of this, but at least we've started."
Showcasing the Green and Golden Bell Frog
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The now endangered Green and Golden Bell Frog (Litoria aurea) has gone from being one of the most common frogs on the eastern seaboard in the 1960s to being listed as endangered in the 1990s. They've disappeared from about 93 per cent of their range in less than 35 years. It's a frightening decline.
"They're the frog species that I grew up with, all of the kids who are of my generation, we all used to keep Green and Goldens because they were the common frog, and they were a pretty frog, and they were just everywhere," said Dr White.
There are many reasons for the decline in the Green and Golden Bell Frogs, all of them related to human activities.
A sad tale
The process started with habitat destruction. Green and Golden Bell Frogs traditionally used coastal lagoons as breeding sites but these have progressively been drained, filled-in or polluted to a point where they are no longer suitable for the frog.
Dr White said another problem is the fact that exotic fish introduced into the rivers of Eastern Australia - in particular the Top Minnow, Plague Minnow and Mosquito Fish (Gambusia) - like to eat Green and Golden Bell Frog eggs and tadpoles.
"Even if there are eggs around from other species of frogs, Gambusia will pick out the Green and Golden Bell Frog eggs and go for them," he said. "Green & Gold Frog tadpoles also tend to float in open water and they just get cleaned up."
...with an ironic twist
Curiously, while most frogs like clean, quiet, undisturbed environments, there's nothing a Green and Golden loves more than an old brick pit or a disused quarry.
As Dr White explains, the trouble with liking 'lovely clean swamps' is that everybody else likes it as well. "Green and Golden Bell Frogs are known as a colonising species, they're constantly on the move looking for a new home," he said.
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"They are a highly mobile species, they spread over a whole range of different habitats and circumstances, they produce one of the biggest clutches of egg masses of any of the Australian native frogs, and they breed prolifically."
Unlike most other Australian frogs, they can even tolerate salty water and some pollution from heavy metals. So, if quarries, pits, mines, industrial sites and building sites are such good habitat for the endangered frog, why are they endangered?
"You do tend to wonder how on earth a species like that could be in such diabolical trouble," Dr White said. "When you really start to look at what we've done to them, it's a tragedy. We've been utterly irresponsible in the way we've treated Bell Frogs."
Want to give frogs a helping hand?
Frog ponds are easy to establish in most backyards, and they provide much-needed frog habitat. Other initiatives, such as fostering frogs who have travelled across the country with farm produce, frog relocation programs and a busy frog rescue service are all part of the work of bodies such as the Frog And Tadpole Study Group (FATS).
No matter where you live, FATS can provide all the froggie advice you need to create a frog-friendly environment for your local frog species.
Contact FATS via email, or write to them (PO Box 296, Rockdale NSW 2216) or just check out the FATS website.
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Links
Australian Frog Groups
There are three groups specialising in Australian frogs which have active websites. They are spread across the eastern States and they're all keen to hear from you if you're interested in helping protect our native frogs:
Australian Amphibian and Reptile Groups
If there isn't a frog group in your home State or Territory, you might want to try a herpetology group. Herpetology is the study of reptiles and amphibians which includes, of course, frogs. In fact, most herpetology societies in Australia have a dedicated frog sub-group:
National:
State, Territory & Regional:
- The Orana Herpetological Society (NSW)
- South Coast Herpetological Society (NSW)
- The Herpetological Society of Queensland
- The Victorian Herpetological Society
- The Western Australian Society of Amateur Herpetologists
- Queensland Frog Society
Information on frogs
Just want the low-down on frogs? Try these sites:
- Australian Frogs: An Australian Museum Information Disk
- The Interactive frog Dissection
- Amphibian Declines in Australia
- Identifying Tasmanian Frogs
Other Herpetology links
If you're still looking for more froggie information and contacts, these pages contain lists of information that shouls help you find what your're after:
Credits
Thanks to Dr Arthur White, President of the New South Wales Frog and Tadpole Study Group and Research Associate at the Australian Museum in Sydney.
Tadpoles on the hop was written by Dr Paul Willis .
Published March 2001
