One of the frogs of northern Australia: the Scrub rocketfrog
Anyone who has ever sat outside in the evening after fresh rain
in many parts of northern Australia will have heard a frog chorus,
sometimes so loud it drowns out conversation. Northern Australia is
not short of the odd frog or two — or to use the
scientists’ term frogs are ‘abundant’ in parts of
Australia’s tropical savannas. There is also a reasonable
diversity of frogs in northern Australia — around half of the
216 species of frogs native to Australia can be found in the
It is perhaps not surprising that there are reasonable numbers
of frogs in Australia’s north. Frogs are amphibians, a term
which comes from the Greek for 'double life' referring to the fact
that many frogs start life as eggs, and then become tadpoles which
live in water, and subsequently sprout legs, lose their tails and
live on land as adults. While not all frogs need to lay their eggs
in water, they all need moist environments.
Far northern Australia, like parts of far southern Australia,
has very low variability in rainfall, i.e. reliable rainfall.
However, this rain tends to fall in the wet season with large areas
of the tropical savannas being very dry for several months of the
year and this is a challenge for frogs.
Why do frogs need moist conditions?
This reliance can be traced back to the ancestry of amphibians.
Amphibians were one of the first groups of animals to evolve from
fish and develop adaptations to living on land, but they generally
retained features that made them dependent on water such as the
need to reproduce by laying eggs in water.
While fossil evidence indicates some early amphibians were quite
large with scaly skins that may have retained water well, modern
frogs appear to have adopted a different solution to survival: they
are small with a skin that is more permeable to water and air and
that assists with breathing. Indeed the skin must remain reasonably
moist so that oxygen can pass through the skin and enter the
This means frogs are not found where it is too dry (the Sahara
desert in Africa and Saudi Arabia) or too cold (Siberia, Greenland
and Antarctica) as shown below.
Distribution of frogs (including toads) —
red areas support frog populations, yellow areas are too cold or
dry for frogs (from Tree of Life website www.tolweb.org/tree)
A green tree frog and a moist habitat
Cyclorana australis Like others in this genus it burrows in
the ground and can store water for long periods in its body
How do frogs survive in the drier parts of northern
Despite their dependence on moisture, frogs are found through
much of arid Australia due to their remarkable ability to exploit
what little water there is in these environments. These adaptations
also prove useful in northern Australia which has severe dry
seasons where little, if any, rains falls for months at a time.
Frogs cope with this seasonal ‘desert’ quite well:
many live in areas with permanent water, while others can lay their
eggs in temporary ponds. Northern Australia has many such ponds
that form in the wet season and then evaporate in the long dry
season and which are good homes for frog eggs as they have few
predators. They are often to be found teeming with tadpoles. By the
time the ponds dry out the tadpoles have developed into small frogs
which then find refuge in cracks in the soil, crevices in timber
and trees. Others use refuges provided by people — a familiar
example being the green tree frog (Litoria caerulea) which
lives in down-pipes and toilet bowls.
However some frogs do not need toilets or even ponds to survive.
Around one-third of Australian frog species can burrow into the
ground to escape dehydration. Burrowing frogs typically have round
bodies and short limbs adapted to digging. Some burrowing frogs can
form a cocoon of dead skin cells around their bodies when they are
in the ground to limit water loss.
The giant frog Cyclorana australis is found in western
Queensland, across the Top End of the NT and in the Kimberley. Like
some other members of this genus, it can spend much of the long dry
season buried underground. It stores water in its bladder and in
pockets under the skin and evaporation is reduced by a cocoon of
shed skin. Once the rains arrive this frog breaks through the
cocoon and emerges from the ground.
Are all tadpoles free-swimming?
No. Several frog species raise their tadpoles in more
protected environments. For example, the northern gastric-brooding
frog Rheobatrachus vitellinus which was found in the
rainforests of north Queensland raised its tadpoles in the
female’s stomach. When they were further developed, the
froglets were regurgitated. Unfortunately, gastric brooding frogs
have not been seen in the wild since 1985.
What’s in a croak?
With rain comes the opportunity for frogs to mate and lay eggs
in water, and for most frog species the mating season involves
advertising. When conditions are good for mating male frogs will
sit around and call to prospective females letting them know that
here is a healthy single male frog sitting next to some nice water
for egg-laying and who is interested in having a good time.
Each species has a distinct advertising call —
presumably to better target appropriate partners. Calls range from
the more conventional "crawk crawk" of the common green tree
frog Litoria caerulea to the barking sounds of the
white-lipped tree frog Litoria infrafrenata of Cape York
Peninsula, the growling call of the growling green eyed frog
Litoria eucnemis of Cape York Peninsula and the chuckling of
the northern laughing tree frog Litoria rothii. A call that
is increasingly being heard across the north is the continuous
mechanical “nock nock nock nock” mating call of the
There are also reports of some frogs calling for other purposes,
such as a 'rain call' in response to rainfall, and the 'release
call' issued by males when other males attempt to mate with
Most frog calls are made with the mouth closed by drawing air
through the larynx. Often the call may then be amplified by a sac
of skin under or around the throat. Some frogs, however, will make
distress calls with the mouth open.
What do frogs eat?
Most adult frogs eat live invertebrates of various kinds and
will usually need moving prey. Often frogs are not fussy and the
diet varies with the availability of prey, for example winged
termites will form a much larger part of the diet when they are
swarming. The cane toad is particularly unfussy and appears to eat
most small things than move and many things that don’t move
— like pet food.
Go to the navigation bar at left to keep reading about the
types and diversity of frogs and the threats to frogs.
Department of Environment and Heritage (2006)
Infection of Amphibians with Chytrid Fungus Resulting in
Chytridiomycosis – Background Document for the Threat
Abatement Plan, Commonwealth of Australia, Canberra
Hero J.-M., Morrison C., Gillespie G., Roberts
J. D., Newell D., Meyer, E. McDonald, Lemckert F., Mahony M.,
Osborne W., Hines H., Richards S., Hoskin C., Clarke J., Doak N.
and Shoo L. (2007) Overview of the conservation status of
Australian frogs. Pacific Conservation Biology 12, pp
Roleants K., Gower D.J., Wilkinson M., Loader
S.P., Biju S.D., Guillaume K., Moriau L., and Bossuyt F. (2007)
Global patterns of diversification in the history of modern
amphibians. Proceedings of the National Academy of Sciences
Tyler M. J. (1994) Australian Frogs –
a natural history. Reed Books, Chatswood NSW