Wednesday, 18 May 2016

South-east Queensland's secret frog

As a subtropical city, Brisbane has a rich and visible frog fauna, with forty-one native species (and one cursed toad) calling it home. Familiar to most people would be that friendly windowsill giant, the green treefrog (Litoria caerulea), and anyone with a garden pond would also perhaps be acquainted with the striped marsh frog (Limnodynastes peronii).

Sharing our suburbs and green spaces, however, are a whole host of other fascinating amphibians that many South-east Queensland residents may never notice or know much about. It’s a fair assumption to make, for example, that Kippa-Ring locals wouldn’t ever suspect that on balmy spring nights, patches of nearby sandy soil suddenly erupt with ornate burrowing frogs (Platyplectrum ornatum). Nor would dog-walkers along Bulimba Creek deduce that among the streambank rubble on which their puppy plays lives a little fellow called the stony-creek frog (Litoria wilcoxii), who turns a bright lemon-yellow colour when he’s ready for some lady-lovin’. 

As winter approaches and the temperature (mercifully) begins to drop, most of these little Kermit characters become hard to find. There’s one exception, however, and as the days get shorter and the nights get longer, he’s only just getting started.

Meet the great brown broodfrog.

Great brown broodfrog, Southport; Photo by Narelle Power

A good father
Broodfrogs get their name because they offer parental care to their offspring, something of an uncommon—though not unheard of—quality among amphibians. Specifically it is the male that offers the care; he makes a damp little nest beneath some debris in a low-lying area, and encourages any female within earshot to drop by, mate and leave her eggs in his custody. 

Competitive edge
The great brown broodfrog (Pseudophryne major) is almost unique in its habitat and range for being an autumn/winter breeder. The tadpoles partially develop inside their eggs during this time, and then lay dormant until rain inundates the nest and washes them into temporary floodwaters. Here, their advanced state is likely to give them the upper hand over the younger, spring-bred tadpoles of other species, and allows them to reach metamorphosis before the waters dry up.

Independent tadpoles
Broodfrogs may start out life in a cosy little egg chamber, guarded by a watchful Dad and surrounded by their brothers and sisters, but once they hatch into the floodwaters, it’s every tadpole for themselves! Their solitary nature at this stage allows them to be told apart from cane toad (Rhinella marina) tadpoles, which are small and dark like those of the broodfrog, but more likely to be found in a dense school.

Typical great brown broodfrog habitat: disturbed, grassy paperbark forest, Meldale.

Swamp lover
Because their breeding strategy involves the use of floodwater, great brown broodfrogs inhabit areas of forest, heath and grassland that become inundated from time to time. Poorly-drained habitat like paperbark woodland is ideal: it’s dry for a considerable portion of the year, but becomes a still, sheltered swamp once there is good rain.
Albino great brown broodfrog, Southport; Photo by Narelle Power.

All great brown broodfrog photos in this article 
have very kindly been supplied by South-east 
Queensland wildlife photographer, Narelle Power. 
Together with photographer Ed Meyer, and authors
Damian White and Jean-Marc Hero, Narelle's work
is about to be featured in a brand new Loders Creek
Catchment Association publication, 'Frogs of the 
Gold Coast'.

Sometimes a beauty
Large for its family but small for a frog, the great brown broodfrog grows to 40mm in length, and is sometimes quite an attractive species. The reason for the ‘sometimes’ disclaimer is that it’s also a very variable species in terms of appearance, with its main surface colouring ranging between tawny brown, dull grey and warmer red tones. Michael Tyler's 'Field Guide to the Frogs of Australia' suggests identifying this species by its light-coloured forehead and the yellow patch on its upper arm, but Gold Coast-based frog expert Narelle Power has noted these features can be inconsistent, and finds its distinctive call to be the real “ID clincher”.

Short and sweet
The demand for good nesting sites is high among male broodfrogs, so quite often they end up breeding—and therefore calling—in close proximity to one another. Standing nearby and listening to a chorus of their raspy little chirps might be as close as you get to these creatures, as they are otherwise concealed fairly well.


Identity challenge
Most similar to the great brown broodfrog is the copper-backed broodfrog (Pseudophryne raveni). It too is fairly variable in colour, and is best told apart by its longer, more drawn-out call. If relying solely on appearance however, it is smaller than the great brown broodfrog, and less likely to have a pale forehead and yellow upperarm.

Family portrait
Northern corroboree frog; Image courtesy of
Australian National Botanic Gardens.
The broodfrog family consists of fourteen species that are unique to Australia. All of them display breeding behaviour similar to the great brown broodfrog, wherein their dependency on standing waterbodies is reduced—a handy adaptation in a drought-prone country. Most famous are the two species of corroboree frog (Pseudophryne pengilleyi and P. corroboree) found in the Australian Alps. They build their nests in the sphagnum bogs of the high country during summer, when this sensitive environment is vulnerable to drought, fire, feral livestock and human disturbance. Numbers of these incredible little frogs have declined severely in recent decades, and they are now listed as Critically Endangered. 

Amphibian alchemy
The broodfrogs have a secret defensive weapon that is still in the process of being understood by scientists: they have toxic skin. This has led to some researchers likening them to the famous poison-arrow frogs (Dendrobatidae family) of Central and South America, but studies have revealed that unlike the latter frogs which create their toxin through a carefully selected diet, the broodfrogs naturally produce their own. In fact, the toxin—the only known alkaloid produced by a vertebrate animal—is so unique that it has been named pseudophrynamine after the broodfrogs' scientific genus name, and shows potential as treatment for chronic pain and heart conditions.

A keelback laying in wait for prey inside a drain, Meldale.

Appetite for danger
The fact that they are toxic doesn’t make a broodfrog completely invulnerable to predators, however. Sharing their swamp habitat in South-east Queensland is a species of snake—the keelback (Tropidonophis mairii)—with a constitution strong enough to prey on cane toads, so it stands to reason that it possibly preys on broodfrogs as well. It is the sole Australian representative of a South-east Asian family of snakes that has evolved alongside many toxic amphibians, though ironically, the keelback is a toxin-free non-venomous species itself.

Queenslander
The great brown broodfrog is found mostly in the coastal southern half of Queensland, extending as far inland as Carnarvon Gorge. It is a fairly tough little frog that can handle a degree of habitat disturbance, and as such, manages to survive in areas as built up as Chermside, Toowong and Southport. Further out of the urban areas, populations thrive in places like Moreton Island, Karawatha Forest and the Pumicestone Passage area.

Tough but not invulnerable
Despite its persistence in surviving alongside us, the broodfrog—like all frogs—is sensitive to human impact. Its favoured living areas are the paperbark swamps and wetlands that many Queenslanders would rather see turned into sprawling, anonymous housing estates. Because these suburban developments are so often built on floodplains, the entire surrounding area, including some of the remnant plots of natural habitat, will usually undergo flood mitigation processes, and of course, the broodfrog requires annual flooding to survive. And if that wasn’t enough to deal with, frog species around the world are suffering from an aggressive, lethal fungal disease that was only identified less than twenty years ago, and still runs rampant throughout the broodfrog’s range. Brisbane is the former home of not one, but two species of frog that were once common but are now extinct. When it comes to conservation, nature has shown that there is no room for complacency.

Great brown broodfrog, Southport; Photo by Narelle Power.

4 comments:

  1. I found this a fascinating post about the Toads. Thanks for sharing.

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    1. Thanks very much, Margaret, glad you enjoyed it!

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  2. Very interesting post Christian!

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    1. Thanks Liz, I'm sure if you keep an ear out in your neck of the woods, you'll find these guys too! :)

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