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.
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| Northern Sedge Frog (L. bicolor) from Fogg Dam in the Northern Territory In this case, this frog can be identified by range. |
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| Sedge Frog (Litoria cf. bicolor) from NE Queensland. Although this best matches descriptions of L. bicolor, it is difficult to be certain. |
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| 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.
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| 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 -
And here's the call of the Northern Sedge Frog (L. bicolor) -
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
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