Eastern vs. Northern Sedge FrogsDrymomantis fallax vs. Carichyla bicolor

 Australia has several species of small grassland frogs called Sedge Frogs.  They are sometimes called Dwarf Treefrogs but I think the name Sedge Frog is more descriptive of their grassy habitats.  All the Sedge Frog species are small green frogs with a brownish border running from their nose through their eye towards the rear of their body.  They can be green or tan, with or without a brown stripe down the back.  

2025 Note - I am aware these two species have been put into to separate genera recently.  They are now known as Drymomantis fallax and Carichyla bicolor.   I will have to decide whether to go through all my frogs from the Pelodryadidae to decide when and whether to update them.  It will mean a LOT of updating. 😭

Northern Sedge Frog (L. bicolor) from Fogg Dam in the Northern Territory
In this case, this frog can be identified by range.

Sedge Frog (Litoria cf. bicolor) from NE Queensland.
Although this best matches descriptions of L. bicolor, it is difficult to be certain.

Eastern Sedge Frog (Litoria fallax) from NE Queensland.
In this case, the species identity could be confirmed by call.

The Eastern Sedge Frog (Litoria fallax) is found along the east coast of Australia from the tropics near Cooktown south to Victoria.   The Northern Sedge Frog (L. bicolor) is found from tropical NE Queensland across the northern part of the country to Kimberley Region of Western Australia.   On the map below, the Eastern Sedge Frog is represented by the golden color, the Northern Sedge Frog by the teal color and you can see their area of overlap in NE Queensland by the lighter blue region.  This is where I ran into trouble with the two species.

Range maps for Litoria bicolor (teal) and Litoria fallax (gold) showing region of overlap.
Shape files downloaded from the IUCN Red Book and overlayed onto Google Earth

While trying to identify frogs in that overlap area, I found myself struggling to distinguish between these  two species.  They can be green or tan, with or without a brown stripe down the back.  Field guides say that they can be distinguised sometimes by the fact that L. bicolor more often has a dark stripe down its back, but both species can show that character.  Supposedly the dark stripe on the Northern Sedge Frog (L. bicolor) goes further back onto the "tail", whereas it tends to fade on the Eastern Sedge Frog (L. fallax).

Now obviously if you've read any of the other "similar species" comparisons I have on my blog, you would expect me to say, "but fortunately, their calls are very different and easy to distinguish".   But in this case that isn't true.   Their calls are different and can be distinguished but the difference is more subtle and can be hard to discern when listening to a chorus.

Both species have a call that consists of one or two "chuck" sounds and an upward slurred raspy trill.  The trill sounds like a fingernail over a very delicate comb.

Here's the Eastern Sedge Frog's (L. fallax) call - 

Eastern Sedge Frog calls

And here's the call of the Northern Sedge Frog (L. bicolor) -

Northern Sedge Frog calls

Hear the difference? It is pretty subtle.

The difference lies in the order of the "chucks" and "trills".  Although both species make one or two "chucks" and a trill, the order is different.  The Eastern (fallax) makes a trill followed by one or two "chucks".   The Northern (bicolor) does the opposite, a trill followed a "chuck" or two.

So the Eastern Sedge Frog calls trill-chuck-chuck (or trill-chuck).

The Northern Sedge Frog calls chuck-chuck-trill (or chuck-trill). 

The tricky part is if you are listening to a big chorus, it can be hard to figure out who is starting where?!

Listen to this group and see if you can tell if it is chuck-chuck-trill or trill-chuck-chuck?

How about this one?

The first recording was Northern, the second recording was Eastern. Simple, right? 😆

Here's a visual showing the two species on a spectrogram.  You can see the different arrangement of chucks and trills.  Ignore the differences in frequency (pitch).  That is temperature dependent, not species dependent.  They were recorded at different times (years!) in different places with different recorders and microphones. 

I had the hardest time telling these things apart in NE Queensland until I heard what could only be Northerns in the Northern Territory.   Once I heard their calls, I understood and could hear the difference.

Now I want to go back to NE Queensland to try and hear them again.  Who am I kidding? Any trip to NE Queensland for any reason would be fine. 😉

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© Chris Harrison 2025

Eastern Sedge FrogDrymomantis fallax

The Eastern Sedge Frog (Drymomantis fallax) is a tiny green hylid found on the east coast of Australia.  These frogs were photographed near Mareebra Wetlands Park in Queensland.

These Sedge Frogs were calling from a garden pond in a group of villas we were staying in within the town of Port Douglas.  The call consists of a dry upward trilling interspersed with a few clicks.

From my limited experience and research, this species is very similar in size, shape and behavior to the Northern Sedge Frog (Carichyla bicolor) and can be very difficult to distinguish in NE Queensland where they overlap.  Supposedly there is a difference in their calls, but I am still working on learning that difference.  The written descriptions have not been that helpful so far but a CD of the recordings that I bought online has helped me understand the difference a bit better.

Here is a single recording of a Drymomantis fallax from near Lake Mitchell, QLD -

and here is the spectrogram of that recording -

You can see that the call consists of a longer upward buzzy trill followed by a number of shorter sharp "clicks".  The number of clicks following the trill seems to vary from 1 to 3 (or a few more).

I am going back over my Australian recordings to see if I recorded any Carichyla bicolor, but for comparison I have created a spectrogram of a single call of a Carichyla bicolor from David Stewart's excellent recordings* -

The obvious difference is the series of clicks prior to the upward trill of the call.  To the ear, this sections sounds like a quick double click, and upward buzzy trill and a follow-up double click.  Once again, the number of clicks after the trill varies but it is the pre-trill clicks that seem to distinguish this species.  In 2025, I added a comparison post between these two sedge frog species.

© Chris Harrison 2014

* I highly recommend David's excellent frog call CD's to NE and SE Australia (http://www.naturesound.com.au/cd_frogsTNE.htm and http://www.naturesound.com.au/cd_frogsSE.htm) for anyone interested in learning or studying Australian Frog calls.  I purchased two CD's from him online and they arrived in the US within a week!