#46 The sad face of a Green Tree Frog

Green Tree Frogs with their ho-hum expression, warty throat and long, clumsy-looking digits, are absolutely delightful creatures. But I haven't always been so endeared to these large green amphibians that used to glare at me from the toilet bowl several times a day.

There was a time, I am embarassed to admit, that I wouldn't use the toilet unless my 7 year-old son was at home to retrieve this fellow from the bowl. And then he'd be back again; and again. Indoor toilets are no guarantee that you'll never be surprised by this fellow either. If they want to get in, they'll get in.

But how could you not love this face?

Amphibian means 'two lives'. Most amphibians are charactised by a distinctive aquatic larval stage called the tadpole. These tadpoles metamorphose into the adult form and then usually leave the water in which they developed. Typically, tadpoles develop in fresh water, and amphibians in general have a low tolerance of saline conditions.

Most larval amphibians possess gills, while adults are air-breathing and possess lungs. All are cold-blooded.

With the exception of toads, frogs usually have a moist, highly permeable skin, and therefore, in order to avoid dehydrating must live in moist places. Even desert species are usually found close to water, and are usually only active after rain.

Green Tree Frog - Litoria caerulea

Tree frogs have astonishingly adhesive toe pads which enable them to climb all types of surface including glass. The Green Tree Frog is probably Australia's best known frog and is found throughout the eastern and northern parts of the country.

Green Tree Frogs sometimes have white irregular spots

This docile frog is one of the biggest frogs (up to 10cm), and although found in many types of habitat, it is usually found around human habitation in mailboxes, meter boxes, downpipes, bathrooms and toilets. In their natural environment they hide in hollow tree limbs and rock crevices.

I evicted this frog from the toilet at my parent's house and found him a nice damp spot by the 'frog pond', but surprise, surprise, he found his way back to the toilet.

Green Tree Frogs, Litoria caerulea, are nocturnal and will emerge from their daytime sleeping hide after dark to feed on insects. It will take anything that fits into its gaping mouth, often shoving it in with its hands. Occasionally I find one on my back porch taking advantage of insects attracted to the outside light.

As well as calling to attract a mate during spring and summer, Green Tree Frogs call at other times, especially during or after rain. Its native predators are snakes, lizards and birds.

Frogs' eyesight and hearing

Frogs need good eyesight as they usually only eat prey that is alive and moving, therefore they generally have large, bulging eyes. They are located on top of the head to allow a wide field of view. As frogs are nocturnal, their night vision is generally well developed.

A frog can protect its eyes with a transparent 'eye-lid' called a nictitating membrane. This transparent membrane permits the frog to see underwater.

The transparent eye membrane

A frog hears through a circular eardrum (the tympanum) located on each side of its head behind the eye. Sound enters the ear via the tympanum which vibrates back and forth. Fluid-filled sacs of the inner ear trigger neural signals which travel to the brain.

The tympanum (eardrum) behind the eye

Frogs make their calls with the help of one or two pouches of skin called vocal sacs. Sound is produced when air rushes over the vocal chords on its way from the lungs into the vocal sacs. The vocal sacs work like echo chambers to amplify the sound.

Conservation

Unfortunately, I don't hear the call of the Green Tree Frog in the Hunter Valley as frequently or in such numbers as when I was a child. Populations are thought to be declining due to habitat modification (land clearing, introduction of invasive weeds, filling of ditches and drains), and pollution.

The thin, porous skin of frogs and tadpoles makes them sensitive creatures. Through this skin, they absorb chemicals from the air and water, therefore, in areas where water or air pollution has occurred, the local frog community will be affected and there are likely to be very few frogs.

Well, come on in - no need to knock

In order to create a healthy environment in which to encourage frogs to live in your garden, you will need to supply clean water such as a small pond with some surrounding vegetation for protection; keep the use of chemical fertilizers, herbicides and pesticides to a minimum; and control pets.

Frogs will need help and consideration from all of us (industry and residential) if they are to thrive as they should.

The night-time frog chorus of several frog species in the paddock adjoining our house-yard following prolonged periods of rain over summer in the Hunter Valley, is an encouraging sound indeed.