“Where’s he going?” Radio-tracking frogs in the Macquarie Marshes

By painstakingly tracking two species of frog in inland NSW, we’ve found out that not all frogs respond to rain and floods in the same way- what moves one species doesn’t always move another.

Standing under the stars, up to our knees in water with mozzies biting through our clothes and midges flying in our faces, we’d point the antenna, tune the radio-receiver and try to hone in on the beeping coming from the tiny transmitters we’d earlier attached to the frogs.

This was the scene in the spring and summer of 2010-11, when my team and I were conducting a radio-tracking study on two of the more common frog species in the Macquarie Marshes, the barking marsh frog (Limnodynastes fletcheri) and the green tree frog (Litoria caerulea). The aim of the study was to determine if there were different influences on the movement and habitat use of frogs. We were particularly interested to see if frog movement and habitat use changed during a very large flood occurring in the Marshes at the same time.

The Macquarie Marshes are a large floodplain wetland in semi-arid NSW, about two hours north of Dubbo, fed by the Macquarie River. The “Marshes” are one of the largest remaining freshwater wetlands in the Murray Darling Basin and are of conservation significance, as some of the largest waterbird breeding events recorded in Australia have occurred there.

Floods in the Marshes have decreased since the river was regulated with dams and weirs, and consequently the Marshes aren’t as healthy as they used to be. Increasingly, controlled releases of water from upstream dams (‘environmental flows’) are being used to breathe life back into this wetland community. We hope that these flows allow frogs to breed and move around the normally rather arid system. But the truth is, we don’t know how these frogs behave, and if the flows are of any benefit to the frogs we are trying to conserve. So, I set about rectifying this!

My PhD was the first extensive study of frog ecology in the Marshes, and one of very few in inland Australia generally. There is very little known about how either of these species move around the landscape and what weather or environmental conditions cause frogs to move or stay put. Answering these questions was going to be important for me to understand what influence the flooding patterns of the Marshes might have on its frog community.

One of the hardest parts of the research was catching the frogs to be able to attach the transmitters! We spent hours wandering wooded areas looking for green tree frogs, or hunting down a calling barking marsh frog. By the end of the study, we’d tracked a total of 63 frogs. We located each frog during the day, and twice at night. There was always a sense of anticipation before we set out, which frogs would have moved this time? How far had they travelled? Where were they going?!

The furthest distance moved by a frog in one night was by a barking marsh frog, at 383m, which I thought was very impressive for something about the size of the palm of my hand. The furthest a green tree frog travelled was 226 m.

More interestingly, each species moved further in different weather conditions. The barking marsh frogs moved regardless of temperature, rain or humidity, but appeared to move less on windy nights. Green tree frogs, on the other hand only seemed to venture far when it had rained during the week and it was a bit warmer. The flood itself didn’t seem to affect movement of either species, though barking marsh frogs used floodwaters to breed in (we heard males calling and caught tadpoles). Green tree frogs didn’t appear very interested in the flooded areas at all.

Our research revealed that not all frogs respond to floods in the same way. As a result, environmental flows probably are only going to directly benefit some frog species, whereas others are likely to ignore flooding, and respond much more to weather. This information is likely to help managers ensure water releases target the habitat of barking marsh frogs and other similar species, and the water remains for long enough that tadpoles turn into little frogs.

It seems knowing the little details, like how far a frog can move, and what triggers this movement, can have a big impact on conservation efforts for frogs of inland Australia.

Dr Joanne Ocock
Research Associate, Charles Sturt University

More information:
Ocock JF, Kingsford RT, Penman TD and Rowley JJL (2014) Frogs during the flood: Differential behaviours of two amphibian species in a dryland floodplain wetland. Austral Ecology doi:10.1111/aec.12158

I’d like to acknowledge my dedicated team of field assistants: Carly Humphries, Jonathan Windsor, Ashley Soltysiak, Sarah Meredith, Dave Herasimtschuk, Angela Knerl, Diana Grasso, Emma Clegg and Bill Koutsamanis. I also thank Garry and Leanne Hall who supported this study with access to the Mole Marsh, and to my supervisors, Richard Kingsford (University of NSW), Trent Penman (University of Wollongong) and Jodi Rowley (Australian Museum Research Institute), and the Centre for Ecosystem Science at UNSW. Financial support came from the NSW Office of Environment and Heritage and the NSW Frog and Tadpole Study Group.