Surveys – Frog calls

Why do we monitor frogs?

Since 1970, freshwater species show a decline of 76% and frogs and other batrachians are among the most threatened ones. Frogs are important bio-indicators and are even considered a “bellwether species”. It means that they are early indicators of changes or damages to the ecosystem. The analogy is the canary brought into the coal mines as a warning sign for toxic gases.

When frogs start to decline other species are likely to follow. Due to their very permeable skin they easily get affected by pollution and poor quality water. Surveys are essential to study their presence and their numbers.

Monitoring

Frogs are hard to see but easy to hear. We can use this characteristic for the monitoring. Each species has a specific mating call with a different pitch, frequency and duration. (They do not want to attract the wrong species). The calls occur in spring and the first three hours after dark is the best time to hear them. My work with Frogwatch consists of studying 3 different sites once a week during October 2018. Our main goal is to make an inventory of the different species and their numbers. But we will also collect data about the weather (wind, air and water temperature), the habitat (water depth, vertical water drop), and vegetation (aquatic vegetation, shade and evidence of mowing).

This kind of monitoring is highly effective. It is also non-invasive because the frogs are not manipulated and only slightly disturbed by our presence. The data collected is used for many studies in the ACT.

Common species

There are 22 species in the ACT. You will find a short description of the 9 most common ones including their mating call in Figures 1,2 and 3.

Figure 1

Figure 2

Figure 3

Results

Disappointingly, two of our sites were in shocking conditions and we did not hear any frogs during our initial visit. At the first site we noticed that the grass near the pond was mowed which absolutely needs to be avoided. The ACT often delegates the job to contractors that employ inexperienced or non-advised employees. Only Limnodynastes tasmeniensis, Crinia signifera, and Litoria peroni were heard the second night.

The water is also really low this year (Figure 4). It makes the frogs vulnerable when travelling over the long distance between the grass and the pond. It will also leave less time for the tadpoles to develop before the pond eventually dries out in the summer. However, mud cracks can provide a good shelter for some frog species. Climate change will make it (or already has made it) worse. However, frogs only need moisture to live and water to reproduce, which gives non-permanent ponds an advantage: they make it impossible for invasive fish species to survive. The Eastern mosquitofish (Gambusia holbrooki) is greatly limiting frog populations mainly because it preys on tadpoles and frog eggs. Other introduced species such as trouts (Oncorhynchus mykiss and Salmo trutta) are also a problem in some regions.

Figure 4: Pictures showing a very low water level in the pond. Notice the mud cracks.

The second site was also in a deplorable state. (Figure 5)

Figure 5: Arboretum. Surrounds are heavily grazed by kangaroos, the banks are eroded, there is no vegetation and no shade

Reflexion

Apart from being fascinating animals, their decline will have other consequences: more insects such as mosquitoes and less food for birds, reptiles and mammals that use frogs as part of their diet. Frogs also indicates to us that the ecosystem is not in a good condition.

Some solutions could consist of putting some large logs and rocks in and around the ponds.They would provide shelter for frogs and make the mowing almost impossible. Also no-mowing warning signs could be erected.

At the Arboretum, it was surprising that so many trees were planted but none around the ponds. Besides adding vegetation, putting a kangaroo fence all the way around the pond would be useful too. This can not be done for all of the ponds, but adding trees for shade, rocks and logs would already be a good start (Figure 6). Aquatic plants could be introduced if the pond is permanent. (Figure 7)

Figure 6. Jerrabomberra wetlands are an example of a good habitat: large logs, rocks, patches of native grass and aquatic plants

Figure 7. Dickson road wetlands is a good example of rehabilitated urban wetlands on ANU campus. Many frogs are present but we will see below that there is another issue…

One last recommendation would be to avoid pollution and dumping waste in those fragile ecosystems. Have a look a look at this final picture (Figure 8). I think it illustrates the point very clearly:

Figure 8. Dickson road wetlands. While listening to frogs during daytime, I stopped for a moment and started collecting the rubbish that were everywhere in the wetlands…

References:

ACT State of the Environment, Commissioner for sustainability and the environment, 2017, www.environmentcommissioner.act.gov.au/publications/soe/2007actreport/indicators/nativespecies07

Arkansas Frogs and Toads, Frogs and Toads basics, Why are they important? What can be done to help them?, http://arkansasfrogsandtoads.org/frogs-toads/

Cornell Cooperative Extension, Attracting wildlife to your pond, 25 july 2015 http://ccerensselaer.org/environment/ponds/attracting-wildlife-to-your-pond

Frogwatch ACT and region, Gininderra Catchment group, National Water Week – Community Frogwatch census kit, https://ginninderralandcare.org.au/wp-content/uploads/2018/08/Frogwatch-Census-Kit-2008_PDF.pdf

Jansen A  Healey M, 2003, Frog communities and wetland condition: relationships with grazing by domestic livestock along an Australian floodplain river https://www.sciencedirect.com/science/article/pii/S0006320702001489

Gillepsie G.R, 2001, The role of introduced trout in the decline of the spotted tree frog (Litoria Spenceri) in south-eastern Australia, https://www.sciencedirect.com/science/article/pii/S0006320701000210#!

Tyler & Knight, 2011, Field guide of the frogs of Australia, revised edition, http://urlz.fr/7UOd

 

Written by u6761581

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About Biodiversity Conservation Blog

I am an Associate Professor at The Australian National University and convene a (very awesome) course called Biodiversity Conservation. Myself and students in the course contribute to this blog.
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2 Responses to Surveys – Frog calls

  1. Contemporary Conservationist says:

    I love frog surveys! I spent a summer listening for Houston Toads in South Central Texas. Fun times! Great article!

  2. Really interesting story and great photos. Phil

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