A frog census on Scottsdale

By Chris Taylor 
on 02 Nov 2016 
Spotted Grass Frog (Limnodynastes tasmaniensis). Photo Chris and Richard Taylor.

This month has seen two volunteers wandering through the bush on Scottsdale in the semi-darkness, visiting the wetter areas, carrying with them iPads, microphones and thermometers, and performing esoteric rituals. No, we’re not completely crazy, we’re just taking a census of the frog population!  

How do we do that? Well, frogs are small, hide in the reeds and grasses and are most active just after sunset, so are very hard to spot. But they do have one feature that makes the census easy – the males call to attract the females, and each species has its own distinct call. 

So we use the iPad to capture the chorus for reference and can then play it back later to confirm the field observations, giving us a not only a record of the species but also an estimate of the number of individual males.

Why do we do this? Well, it's often said that frog species are a barometer for the health of a wetland ecosystem. They're sensitive to any changes in the environment, partly because of their quite complex lifecycle, and because they have a permeable skin that can absorb harmful materials. So if the wetlands are clean and free from pollution, then we can expect a healthy frog population too.

Last year a monitoring program was run on Scottsdale from June to December, to identify when the frogs were breeding. Recordings were done at three sites on the reserve, and gave us a view of the frogs over that time. 

But this year we wanted to get a much wider picture over more of the reserve. We chose 21 sites covering most of the lower areas, but also extending to the higher country, and visited these over two nights. The best recordings are made after last light, so we set out at sunset to visit each of the sites in turn, which took over 2 hours each night, visiting half of the sites on one night, and the rest the next.

Results

How does Scottsdale fare when it comes to frog health? Quite well, we're pleased to report. These surveys turned up 6 species calling, with as many as 5 calling at the same time at some sites. There are at least 4 other species that we know are in the area, but they were silent this time. Further checks later in the year will pick them up too. 

One thing that we did find was that the creek seemed to have fewer frogs than we expected; but given the record September rains that fell in this part of NSW, the creek would be running too strongly for many species. Away from the creek we recorded good numbers, and saw a few tadpoles and patches of spawn as well, so the populations are certainly in good shape.

Even Phil Palmer, Scottsdale Reserve Manager, got in on the act and obtained a clear recording of a call that was unknown for this area. It raised some excitement for a while as we thought it was a species moving into the area. Unfortunately it turned out to be 'just' the call of a Eurasian Coot. Better luck next time, Phil!

Download the final Frog Report resulting from these surveys.