AUSTRALIAN GROUND FROGS: Limnodynastidae

PHYSICAL CHARACTERISTICS

Although some scientists still believe that the Australian frogs should be divided up differently, this book follows the most common arrangement with two families: the 48 species of Australian ground frogs in the family Limnodynastidae and the 121 species of Australian toadlets and water frogs in the family Myobatrachidae. This entry deals with the Australian ground frogs.

Many of the Australian ground frogs have earth-tone colors, like brown, greenish brown, tan, and gray, often with spots, blotches, or other patterns that camouflage them against the dirt and plants of the ground. They commonly have lighter colored bellies, sometimes with faint patterns on the throat. Some species, however, are quite brightly colored. The northern banjo frog, which is also known as the scarlet-sided pobblebonk, has bright yellow sides with red and orange splashes of color under its legs, and the crucifix (or Catholic) toad has a warty, yellow back centered with a thick, dark brown, cross.

Some of the Australian ground frogs, like Fletcher's frog and the giant barred frog, have a typical frog shape with long, jumping hind legs and a large head. Others, like Spencer's burrowing frog and the sand frog, have shorter hind limbs and a blunter face more associated with toads. Most of the Australian ground frogs have little or no webbing on their front or rear toes.

The different species come in a variety of sizes. The smallest grow only to 0.9 inches (2.2 centimeters) long from the tip of the snout to the end of the rump, while others can reach as much as 4.3 inches (10.8 centimeters) long. Males and females usually look much alike, but in some species, the males develop very noticeable pads on their front toes and front legs during the breeding season. Called nuptial (NUHP-shul) pads, they help the male grab hold of the female during mating.

GEOGRAPHIC RANGE

Australian ground frogs are found in Australia and much of New Guinea.

HABITAT

Many of the species in this family are burrowers and live part of their lives underground. The giant burrowing frog is an example. During the daytime, and also during long, dry periods, this species uses its powerful hind legs to dig backward into the soil and bury itself. This behavior hides the frog from would-be predators and also helps to keep its skin moist. Other species in this family, like the woodworker frog and striped marsh frog, do not burrow. Instead, the woodworker frog hides in the cracks of rocks or in caves, and the striped marsh frog slips among the tall plants of the marshes, grasslands, and forests where it lives. The typical Australian ground frog mates in a stream or pond—sometimes one that dries up later in the year.

DIET

Australian ground frogs eat various types of invertebrates (in-VER-teh-brehts), which are animals without backbones, by either grasping them with a flick of the tongue or by biting at them. Australian ground frogs wait to hunt until night, and some do their hunting only after heavy rains soak the ground. In many species, such as the Baw Baw frog, the tadpoles do not need to search for food. Instead, they live on a sack of nutritious yolk that is left over from the egg and is still a part of their bodies.

BEHAVIOR AND REPRODUCTION

The species in this family are either nocturnal (nahk-TER-nuhl), which means that they are active mostly at night, or crepuscular (creh-PUS-kyuh-lur), which means that they come out only at dawn and dusk. As with the majority of other nocturnal or crepuscular frogs, the Australian ground frogs do not like air that is too dry, as it often is during the day. Instead, they come out when the air starts to become moister, which typically happens at night when the sun is down and the temperature starts to cool off. In addition, many Australian ground frogs will not even venture out at night during especially dry periods. For some of them, such dry periods, called droughts (drowts), happen at least once a year and may last several months. During this time, some of the Australian ground frogs burrow underground to keep from drying out.

Frogs must keep their skin moist to breathe. Like humans and other mammals, frogs can breathe through the nose and lungs. However, frogs also get a great deal of their oxygen right through the skin. If the skin dries out, they can no longer breathe through the skin, and they can suffocate. Many of the burrowing frogs in this family dig into the ground by swishing their powerful hind limbs one at a time and backing into the soil as their body wiggles back and forth. Other species, like Spencer's burrowing frog, dig backward into the soil, but turn their bodies in circles while they are doing it. These frogs look as if they are screwing themselves into the ground. Several species can stay underground for a number of months. They enter a sleep-like state, called estivation (es-tih-VAY-shun), and only wake up and become active again when the heavy spring rains drench the land. The tusked frog is an example. This animal, as well as numerous other members of this family, lives underground inside a cocoon of shed skin for several months each year.

KICKSTARTING LIFE

Giant barred frogs have an odd start to their lives. The female lays her eggs in the water with her back pointing toward the shore. As the eggs drop, she gives them a swift kick with her hind foot, flinging the gel-covered eggs in a splash of water onto shore where the eggs stick to the bank and shore-side rocks. When the tadpoles hatch from the eggs, they plop down into the water and swim off.

Spring rains begin the mating season for most of the burrowing Australian ground frogs. In some of these species, all mating for the year is done within a few weeks' time. Some types of Australian ground frogs breed during certain seasons of the year, and others, like the spotted marsh frog, can mate and lay eggs all year long if the weather is right. Whenever their mating season begins, the males start calling at dusk or at night, usually from ponds, streams, or marshes, but sometimes from on land. Their calls attract females and also keep other males from invading their space. Different species have different calls. The spotted marsh frog, for instance, calls with a repeated clicking noise of "tik-tik-tik"; the giant burrowing frog sometimes goes by the name of eastern owl frog, because its call of "oo-oo-oo-oo-oo" sounds like an owl hooting; and the common spadefoot frog has a knocking trill for its call.

Some of the females in this family lay their jelly-coated eggs in the water, often in a foamy nest. The female typically makes the foam by flailing her feet and whipping up her eggs and the mucus surrounding them. This adds air to the mixture and creates the foam. The eggs hatch into tadpoles, which then swim out into the water, or in some cases, stay in the foam until they turn into froglets. Other females lay their eggs in a foam nest, but make it inside a burrow or among plant leaves and branches on shore. When heavy rains flood the nest, the eggs hatch into tadpoles, which then live in the water.

AUSTRALIAN GROUND FROGS AND PEOPLE

Because many of these species burrow or otherwise stay out of sight during the day, people rarely see them. For some people who live in the deserts of Australia, however, a few of the burrowing species can be a good source of water. They dig up the frogs, whose bodies are plump with stored water, and suck the liquid from the frogs. Besides this unusual use, scientists are also now studying the slime of some species perhaps to make medicines.

CONSERVATION STATUS

According to the World Conservation Union (IUCN), one species is Critically Endangered, which means that it faces an extremely high risk of extinction in the wild, and seven others are Endangered, which means that they face a very high risk of extinction in the wild. In addition, IUCN lists two species as being Vulnerable and facing a high risk of extinction in the wild, one species as Near Threatened and at risk of becoming threatened with extinction in the future, and two species as Data Deficient, which means not enough information is available to make a judgment about the threat of extinction.

The Critically Endangered species is the Baw Baw frog, a dark-brown, warty creature that grows to about 2 inches long. It lives in tunnels in wetlands or under cover alongside streams in a small location on the Baw Baw Plateau, which lies in an area east of Melbourne. Although part of its habitat is inside the Baw Baw National Park, the frog's numbers have dropped from more than 10,000 individuals in 1985 to fewer than 250 adults in 2004. Scientists are unsure exactly what is causing the Baw Baw frogs to disappear, but they think that dangers may come from a warming climate, infection with a type of fungus, pollution, or an increase in ultraviolet radiation. The sun gives off light in different forms, such as the light humans can see and other types they cannot, like ultraviolet, or UV, radiation. UV radiation is especially strong high in the mountains, which is where the Baw Baw frog lives. Through various experiments, scientists have learned that UV radiation causes death in the tadpoles of other mountain-living frogs and think the same thing may be happening to the Paw Paw frogs. Scientists are continuing to study this species to find out why it is vanishing.

The Endangered species are Fleay's barred frog, the giant barred frog, the red and yellow mountain frog, Loveridge's frog, the mountain frog, the sphagnum frog, and one known only by its scientific name of Philoria pughi. They all live in small areas, and often their habitat is being destroyed or changed by such activities as logging, movements of cattle that can trample the frogs' foam nests, and the building of homes, businesses, and roads. At least some Fleay's barred frogs have also died as a result of infection with a fungus. On the bright side, most of these frogs now live inside reserves or other protected areas, which should limit some of the dangers they face.

TUSKED FROG (Adelotus brevis): SPECIES ACCOUNTS

Physical characteristics: The tusked frog gets its name from the male's two, unusually large, lower teeth, or tusks. The tusks only show if the frog's mouth is open. Otherwise, they are hidden inside. The female either has very small tusks or none at all. From above, the frog is tan with olive, brown, or black blotches on its back and markings that form broken band patterns on its legs. A reddish brown, somewhat triangular-shaped patch covers most of its snout. It has large eyes with horizontal pupils, and its front and hind feet have just a bit of webbing. Once the frog is flipped over, its color changes. The underside is mottled with black and white, and its legs are trimmed in dark orange or red. Unlike most other frogs, in which the males and females are the same size or the females are larger, male tusked frogs are usually the bigger of the two. Males typically grow to 1.3 to 1.7 inches (3.4 to 4.4 centimeters) from snout to rump, but females only reach 1.1 to 1.5 inches (2.9 to 3.8 centimeters) long. In addition, the male's head is larger than that of the female.

Geographic range: Tusked frogs live in the far eastern part of Australia from Queensland to New South Wales.

Habitat: Tusked frogs live in forests and sometimes in grasslands. The males usually stay near water, which may be a stream or just a puddle, but the females prefer drier places.

Diet: Their diet includes snails, insects, and other invertebrates. The males, which tend to live closer to the water, eat more snails, while the forest-living females eat invertebrates they find in their drier habitat.

Behavior and reproduction: Adults tend to stay under leaves and pieces of bark lying on the ground or huddled in some other hiding spot. During the breeding season, the males set up territories and defend them by biting other males with their long tusks. The bites can be severe and may leave scars. Each male calls from his territory with a voice that is a slow, soft "cluck - cluck - cluck." The female lays her eggs on the surface of the water in a foamy nest. The male stays with the nest, which is usually hidden from view under plants or other cover. The eggs, which measure less than 0.08 inches (2 millimeters) in diameter, hatch into tadpoles before changing into froglets.

Tusked frogs and people: People rarely see this frog in the wild or in the pet trade.

Conservation status: According to the World Conservation Union (IUCN), this species is Near Threatened, which means that it is at risk of becoming threatened with extinction in the future. Its numbers have dropped in many areas because of habitat loss, mainly as humans have turned the frogs' home into farmland or housing developments, and also because of infection with a fungus that is harming many species of frogs worldwide. ∎

PAINTED FROG (Neobatrachus pictus): SPECIES ACCOUNTS

Physical characteristics: Also known as the painted burrowing frog, the painted frog is tan, yellow, orange brown, or gray with dark brown or black spots and blotches on its head, back, and legs. The upper body is almost completely covered with small, rounded warts. The frog has short but not thin front legs and longer hind legs. On the toes of each back foot, it has a black bump that it uses as a shovel, or spade, for digging. This bump, which is called a tubercle (TOO-ber-kul), gives the frog another common name, the mallee spadefoot. (A mallee is a shrubby area where a type of eucalyptus grows.) The painted frog has a short head with a rounded snout and two large eyes with vertical pupils. Males and females look similar except during the breeding season, when the males develop tiny spines on top of their warts, giving them a prickly look. Adults grow to 1.8 to 2.3 inches (4.6 to 5.8 centimeters) long from snout to rump.

Geographic range: Painted frogs live in south-central Australia, including South Australia, and likely Victoria and New South Wales.

Habitat: The painted frog lives in an area that typically has a very dry season and a rainy season. During the dry season, it stays underground in open forests or shrubby areas. In the wet, breeding season, it is found in grassy marshes, small ponds, and various pools of water.

Diet: The painted frog probably eats insects and other invertebrates, but scientists have not studied them closely enough to say for sure.

Behavior and reproduction: At the beginning of the dry season, this frog digs down into the soil. Once in a suitable underground spot, the outer layer of its skin peels up from its body, but stays in one piece and attached to the frog's body to form a coat, or cocoon. Snuggled inside its cocoon with only its nose poking out, the frog enters a state of deep sleep, called estivation, which lasts until the rainy season begins in fall or winter. Once the ground becomes wet, the cocoon splits open, and the frog digs itself out of the ground. The frog apparently does all of its feeding during the rainy season. It also breeds at this time.

Males of this species, which some people call trilling frogs, float in the water and begin calling. The call is a two- or three-second purring or trilling sound. Males and females meet at marshes or other shallow pools, and the females lay clumps of up to 1,000 small eggs in plants at the edge of the water. The eggs hatch into tadpoles, which may grow to be as much as 3.5 inches (9 centimeters) long from snout to tail tip before they change into froglets.

Painted frogs and people: People rarely see this burrowing frog. Those who handle these frogs must wash their hands, because the frog's warts can ooze a gooey slime that is believed to make people sick if they get it in their mouths and swallow it.

Conservation status: The World Conservation Union (IUCN) does not consider this species to be at risk. Although it is not common, its numbers appear to be staying about the same. Some of the frogs live in protected areas, but others live in places that may be developed into farmland, which could hurt the frogs in the future. ∎

NORTHERN SPADEFOOT TOAD (Notaden melanoscaphus): SPECIES ACCOUNTS

Physical characteristics: Sitting as it often does with its short legs tucked against its body, the northern spadefoot toad has a shape like a golf ball. Some people even call this species a golfball frog. A small head with large eyes and a very short snout barely pokes out of its body. Its head, back, legs, and throat are brown to greenish brown or gray with black markings and are covered with warts. The warts may be tipped in white. Its belly is white. This frog has long, pointed toes and tubercles on its feet, similar to those of the painted frog, which give it the spadefoot name. Females usually grow to 1.8 to 1.9 inches (4.5 to 4.9 centimeters) long from snout to rump. The males sometimes are a bit smaller, usually reaching 1.3 to 1.9 inches (3.4 to 4.8 centimeters) in length.

Geographic range: The northern spadefoot toad lives in northern Australia, including parts of Kimberley, Western Australia, and Queensland.

Habitat: The northern spadefoot toad spends much of its life underground, but comes to the surface after heavy rains. It breeds in marshes, swamps, and small pools of water.

Diet: With the flip of a tongue out of the small mouth, the northern spadefoot frog snatches up small insects and other invertebrates to eat. The tadpoles appear to eat by straining tiny organisms out of the water.

Behavior and reproduction: This species uses the spades on its feet to burrow into the soil. In rainy weather, the northern spadefoot toad digs out of its underground home to look for insects, and in the breeding season, to mate. With its short legs and pudgy-looking body, this frog walks rather than hops and is not able to outrun most predators. It does, however, have a way of defending itself. When threatened, its warts ooze a gluey goop. A predator that unwisely bites at one of these frogs gets a mouth full of goop that quickly hardens, turns bright orange, and becomes difficult to clean off.

In the rainy, breeding season, males move to marshes, swamps, and newly filled pools of water and call from shallow spots. Their call is a loud, repeated "whoop." When the male calls, his body fills with air like a balloon. If he feels threatened, he will let the air out and sink out of sight. Males mate with females by climbing onto their backs and hanging on in front of the females' hind legs. Each female lays 500 to 1,400 eggs on the water's surface, and the eggs later sink and tangle in underwater plants as they hatch into tadpoles. The tadpoles turn into froglets when they are about two months old. The young froglets look much like the adults, but are often speckled with bright yellow, red, and black spots.

Northern spadefoot toads and people: People rarely see this frog.

Conservation status: The World Conservation Union (IUCN) does not consider this common species to be at risk. Some of its populations live in protected areas. ∎

FOR MORE INFORMATION

Books:

Anstis, M. Tadpoles of South-eastern Australia: A Guide with Keys. Sydney: Reed New Holland, 2002.

Barker, John, Gordon C. Grigg, and Michael J. Tyler. A Field Guide to Australian Frogs. Chipping Norton, Australia: Surrey Beatty, 1995.

Campbell, A., ed. Declines and Disappearances of Australian Frogs. Canberra, Australia: Environment Australia, 1999.

Cogger, H. G. Reptiles and Amphibians of Australia. 6th edition. Sydney: Reed New Holland, 2001.

Cogger, H. G., E. E. Cameron, and H. M. Cogger. Zoological Catalogue of Australia. Vol. 1, Amphibia and Reptilia. Canberra, Australia: Australian Government Publishing Service, 1983.

Cronin, Leonard. Key Guide to the Reptiles and Amphibians of Australia. Sydney: Envirobooks, 2001.

Littlejohn, M. J., M. Davies, J. D. Roberts, and G. F. Watson. "Family Myobatrachidae." In Fauna of Australia. Vol. 2A, Amphibia and Reptilia, edited by C. J. Glasby, G. J. B. Ross, and P. Beesley. Canberra, Australia: AGPS, 1993.

Malone, B. S. "Mortality during the Early Life History Stages of the Baw Baw Frog, Philoria frosti (Anura: Myobatrachidae)." In Biology of Australasian Frogs and Reptiles, edited by G. Grigg, R. Shine, and H. Ehmann. Chipping Norton, Australia: Surrey Beatty and Sons, 1985.

Robinson, Martyn. Field Guide to the Frogs of Australia. Sydney: Reed New Holland, 1993.

Swan, Gerry. Green Guide to Frogs of Australia. Sydney: New Holland, 2001.

Web sites:

"Frogs—Amphibia." Wildlife of Sydney.http://faunanet.gov.au/wos/group.cfm?Group_ID=36 (accessed on February 24, 2005).

"Frogs of Australia." Amphibian Research Centre.http://frogs.org.au/frogs/index.html (accessed on February 24, 2005).

"Frogs of North Queensland." James Cook University School of Tropical Biology.http://www.jcu.edu.au/school/tbiol/zoology/herp/NthQldHerps/NthQLDHerps-frogs.shtml (accessed on February 24, 2005).

"The Frogs of NSW Wetlands - Other Frogs." NSW Department of Land and Water Conservation.http://www.dlwc.nsw.gov.au/care/wetlands/facts/paa/frogs/other_frogs.html (accessed on February 24, 2005).

"Information on Protecting Australian Frogs." ASX Frog Focus.http://www.asxfrogfocus.com/ (accessed on March 1, 2005).

"Useful Links and Frog Resources." NSW National Parks and Wildlife Service.http://www.nationalparks.nsw.gov.au/npws.nsf/Content/Useful+links+and+frog+resources (accessed on February 24, 2005).