Bonk...bonk....

Those of you with a wildlife pond have no doubt been hearing the fantastic noise of the Eastern Bango Frogs (Limnodynastes dumerilii) calling for some time now.  The wonderful sound of the frog has given it a very evocative common name in the Dandenongs, the Pobblebonk.

L. dumerilii subspecies dumerilii
the most widely spread subspecies
and common in Melbourne suburbs

It may also be known to some of you as the Four-Bob Frog, Bullfrog or simply Bonking Frog.  Personally, I prefer Pobblebonk to Bonking...

L. dumerilii subspecies fryi
this subspecies is found only in the
Snowy Mountains

These fantastic frogs are native to south-eastern Australia, from Kangaroo Island, out to Tassie and up the coast just into Queensland.  There are actually 5 subspecies that have overlapping areas and can be separated by differences in the webbing on their toes, size, colouration and the presence or absence of a stripe along their backs.

L. dumerilii subspecies insularis
is found along the south-eastern coast of Victoria
and into NSW.  It's the only subspecies found in Tas.

Pobblebonks are a burrowing species, commonly found in gardens under rocks and calling from beside ponds.  They tend to burrow during days in summer and over extended dry periods can actually be heard calling from their burrows when rare rain has fallen.

Sometimes, especially after rain and where the habitat is right, they can actually be found in large numbers.  Despite, they're not actually social creatures.  Mass spawning might also occur when conditions are right.  This, their size and the warty appearance of some of the sub-species, often leads to them being mistaken for Cane Toads, but it must be quite a sight to see!

Now, being burrowing frogs Pobblebonks find it a tad difficult to climb out of steep sided ponds, water troughs and the swimming pools that they quite frequently job in by mistake.  To make sure they, and any other creature that falls into your pond etc can get out, it's a good idea to ensure the side is shallowly sloped, has plenty of rocks etc to make it easy to climb (or for hiding under) and perhaps add a branch or too.  Frogs like to sit on these and they also provide a good spot for algae to grow - yummy tadpole food!

L. dumerilii subspecies grayi

The 'bonk' call is made by breeding males trying to attract a mate and I believe that the females make no sound.  This means that in this species at least, the males do all the talking :)

The call can be heard in low numbers year round, but the main breeding season is September to January.

Although most prefer still, permanent water to breed, subspecies dumerilii will breed in moving streams.  In fact, it will also breed in what was supposed to be a seasonal frog bog that was going to be allowed to dry out completely over summer and consequently now has to be topped up regularly... :)

The females lay a large, frothy white floating raft of eggs in permanent water. There can be around 4,000 eggs and the raft can be across 1.8m in width!  Makes it a bit tricky to hide, yet often they are mostly concealed by vegetation.  The tadpoles spend most of their time near the bottom of their home, feeding on algae and other organic matter in the sediment.  They also like to scrape algae off branches left to sit in the water.

L. dumerilii subspecies variegatus
found in western Victoria and south-eastern SA.
Some reports have it restricted to the Otway Ranges.

The tadpoles can vary in colouration, from brown through dark brown to black, and may also be flecked with darker spots.  These guys are not little either: the tadpoles can attain a length of almost 7cm in the time it takes them to complete development.  According to Museum Victoria, that can be up to 15 months.  You can see why they prefer permanent water for breeding!

What this actually means though is that, like many frogs, Pobblebonks have a great survival technique: some tadpoles will grow very quickly and metamorphose into young frogs within a few weeks, whilst others will remain as tadpoles for over a year.  Although Pobblebonk tadpoles are pretty hardy, survival techniques like these are still important as a large percentage of the tadpoles will not make it to maturity.  Delayed development allows populations to space the emergence of breeding adults over as long a period as possible.  Pretty amazing, huh?

It can also be dependant on temperature and rainfall.  In warmer, wetter areas, development is faster (4-5 months), whilst in colder areas such as the Snowy Mountains it may be 12-15 months.

One of the best things about these guys is that they are a major friend to gardeners.  Like many frogs, toads and reptiles, Pobblebonks are hungry predators liking nothing better than a tasty insect or perhaps several.  Of course, they also eat earthworms, but if like me you have a lot of these, then you probably won't mind sharing a few! :)

As always, your role in encouraging wonderful creatures such as the Pobblebonk into your garden is to make it as friendly as possible.  Provide them with a water source (preferably a fish-free pond), lots of vegetation for cover and places to hide, like rocks and log piles.

Most importantly: keep your garden chemical free and encourage your neighbours to do the same.  Pesticides, herbicides and other garden chemicals are very harmful to wildlife.  Frogs and other amphibians in particular are very sensitive to everyday garden products such as Roundup (Glyphosate) - even in incredibly low concentrations.  Definitely do not use these products anywhere near a water body or source.

There are of course other species of Limnodynastes in Australia and some are very closely related to our Pobblebonk: L. dorsalis, Western Bango Frog; L. interioris, Giant Bango Frog and L. terraereginae, the Northen Bango Frog. 

I love that most populated areas of Australia get to enjoy hearing "Bonk.....bonk.....bonk....." on warm, wet evenings :)

Further reading:
http://keys.lucidcentral.org/key-server/data/050d0302-080d-4b0b-8603-0f05010c030b/media/Html/Lymnodynastes_dumerilii.htm

http://museumvictoria.com.au/discoverycentre/infosheets/frogs-of-victoria/pobblebonk-or-banjo-frog/

http://www.nccma.vic.gov.au/library/scripts/objectifyMedia.aspx?file=KMSMedia/pdf/89/59.pdf&fileName=Pobblebonk.pdf

http://museumvictoria.com.au/accessallareas/liveexhibits/post/pobbles-grow-up.aspx

All images used above are copyrighted and were borrowed from a great book: Tyler, J.M. & Knight, F 2009, Field Guide to the Frogs of Australia, 2011 Ed, CSIRO