Where do frogs live?

There are over 200 species of frog occurring in Australia. Frogs belong to the Class Amphibia, and all are reliant on moisture to breathe, reproduce and generally survive and thrive. Nocturnal life is one way of minimising the risk of drying out, for it is the coolest part of the day. Most frogs are active at night. Despite this drawback of a dependence on water, frogs have evolved and diversified in form to occupy a variety of habitats, from rainforests to deserts, from rock faces to subterranean burrows, from free water to sphagnum moss bogs - frogs are found in a surprising number of different spots.

Reproduction

Most frogs breed seasonally when conditions of temperature, day-length and moisture are right. It is common to see tadpoles (the name given to very young frogs) swimming in ponds at different times of the year. When a female lays eggs the male fertilizes them and the resulting floating mass of eggs (spawn) is left while the frogs develop. Hatching of the tadpoles may take several days, followed by a period when the tadpole develops and finally changes into the adult frog, a process called metamorphosis.

What is happening to the world's frogs?

Frogs eat insects and overall must account for millions of insects daily. They also eat other small invertebrates. By eradicating millions of insect pest species frogs play an important role in maintaining the balance of nature. But something is happening to the environment, both within Australia and internationally, that is alien to frogs. In the past 15 years or so frog populations have declined dramatically, even in supposedly uncontaminated environments such as national parks. Something in the environment is killing the world's frogs. If we accept that frogs are indicator species and this is a warning that environmental changes are taking place, it is in our own interests to take heed of this potential tragedy.

Our local frogs

Several species of frog can still be found, or, more likely heard, in the Australian National Botanic Gardens. At certain times of the year male frogs distend their vocal sacs (situated just below the throat) with air to serve as a resonance chamber to amplify sounds and issue a great variety of calls to attract females. It is common to hear great choruses of different species trilling away, endeavouring to attract mates. Frogs which can be heard in the Gardens, in decreasing order of likelihood of discovery, are:

• Common Eastern Froglet Crinia signifera
• Eastern Banjo Frog Limnodynastes dumerilii
• Spotted Grass Frog Limnodynastes tasmaniensis
• Brown-striped Frog Limnodynastes peronii
• Peron's Tree Frog Litoria peronii
• Eastern Froglet Crinia parinsignifera
• Whistling Tree Frog Litoria verreauxii

Common Eastern Froglet Crinia signifera

A small frog up to 3 cm in size. Extremely variable in colour and pattern. Upper surface pattern of either uniform light grey or brown contrasting with black sides; or grey or brown with irregular darker patches and sometimes a light vertebral stripe; or a broad dark vertebral band bordered on either side by a light brown or grey band from eye to groin. This small gregarious species is common in and around the pools in the Gardens.

Call: "crick-crick-crick"

Eastern Banjo Frog Limnodynastes dumerilii

A stout frog from 6-8 cm in size. Grey or brown with blackish marblings, with or without a continuous or broken narrow vertebral stripe. Sides often beautifully marked with a bronze and purple sheen with black mottling. A pale yellow stripe from below the eye to above the base of the forelimb is conspicuous. Common in ponds around the Gardens.

Call: "bonk-bonk-bonk". Two or more frogs in unison sound like "pobblebonk"

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Spotted Grass Frog Limnodynastes tasmaniensis

Up to 4.5 cm in size. Light brown to rich olive-green above, usually with a series of large, regular dark brown splotches and often with a narrow white, yellow or russet vertebral stripe from snout to vent. Shelters under logs and stones on edges of permanent and temporary swamps, pools and creeks.

Call: a very rapid "uk-uk-uk-uk"

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Brown-striped Frog Limnodynastes peronii

Up to 6.5 cm in size. Light brown above with a series of irregular dark brown stripes. Frequently a pale vertebral stripe from snout to vent. A dark brown band behind eye. Secretive by day, hiding under logs, stones or leaf litter. Burrows effectively.

Call: usually a single "plonk" or "whuck", repeated at intervals of a few seconds.

Peron's Tree Frog Litoria peronii

Medium-sized frog to 6 cm. Rich grey or brown above, varying in intensity with temperature and temperament. Irregular darker mottling and numerous small bright green spots over upper surface. Groin and hind sides of thighs mottled black and bright yellow. May be found long distances from water in a variety of habitats, usually in trees and shrubs. Will forage for food on the ground.

Call: a loud, penetrating long rattle. Has been variously described as a "loud chuckling trill" and a "sound of a pneumatic drill"

Eastern Froglet Crinia parinsignifera

Small frog to 3 cm in size. Almost indistinguishable from the Common Eastern Froglet. Males may only be distinguished by their call. Females have a rather granular white belly pattern while Common Eastern Froglet females have a belly mottled with black and white. Difficult to find this species in the Gardens, although it is present. More experienced observers may pick it out by the different call.

Call: long, low drawn out "squelch".

Whistling Tree Frog Litoria verreauxii

Up to 4 cm in size. Highly variable in colour pattern, this species may be fawn, brown or reddish-brown above. A dark brown stripe extends from the nostril through the eye to the shoulder. Groin pale yellow with black spots. Front and hind sides of thighs are orange. Found in a variety of habitats from swamps, lagoons, wet and dry sclerophyll forest to alpine grassland and bogs. Breeding groups occur around ponds, dams and creeks. One of the few species to call throughout the year.

Call: rapid, pulsing whistle "cree-cree-cree-cree".