They’re Not Frogotten: How Are New Zealand’s Native Amphibians Doing?

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Written by: Emily Stephens

How often have you seen a native frog in your local bush or forest? If your answer is ‘not often’, maybe there’s a reason. It has been well-documented that amphibian populations have been declining steadily in recent years1,2 – documenting as early as 19903. Dangers are around every corner for some of our most vulnerable friends, but human observation and interference is one solution to saving our wildlife.

Figure 1: Archey’s frog. Credit: DOC. Image description: a brown, black, and green frog sitting on a leaf with a text-box that reads: Amphibians help our ecosystem through: controlling invertebrate population; disease prevention; pollen and seed dispersal; nutrient cycling.

How are their populations doing?

New Zealand has only 4 native species of amphibians, all of them endemic frogs.5 A 2017 DOC study6 of amphibian populations showed that although all species of frogs are still threatened or at-risk, 2 have improved their conservation status between 2013-2017. Hamilton’s frog has a small population of ~300 living only on Stephens Island5 but its status had actually improved from the worst conservation status possible. This study found the Maud Island frog to have minimal difference to Hamilton’s frog, so both were counted as one species. It was estimated that Archey’s frog populations had declined by 88% between 1996-2001,7 yet their status also improved. The Hotchstetter’s frog has the largest population size but is still considered at-risk.

It’s important to note that this data was taken in 2017. Populations can change easily with factors such as human interference, and with such small-bodied participants, populations may be difficult to accurately assess.

Figure 2: Estimates of population size (Nhat) of Archey’s frog on the Tapu Ridge study plot between 1983-2003. Credit: Bell, Carver, Mitchell, & Pledger (2004).7 Image description: a vertical bar chart showing population estimates of Archey’s frog on the Tapu Ridge study plot between 1983-2003. Population estimates range between 300-600 between 1984-1994 but drop sharply to population estimates between 50-100 between 1996-2003.

What causes declines?

The most likely causes of population decline are predation, habitat destruction, disease, and pollution.8

  • Our native frogs are particularly susceptible to rats and cats because they evolved without mammalian predators. When Polynesian settlers brought kiore, or when European settlers brought rats and other mammals, native species suddenly had new predatory threats and competitions for resources.9
  • Frogs absorb chemicals through their skin so are also more susceptible to environmental changes and pollution.5
  • Diseases such as amphibian chytrid fungus can be spread through frog interactions, water ways, or even through humans spreading diseased soils or water.5
  • Most of our native frogs give birth to live young so cannot breed quickly.5 This makes them more vulnerable to population loss because they cannot restore lost populations.

What’s being done?

NZ’s conservation management (including DOC and Auckland Zoo10) have been providing predator control on offshore and mainland islands through methods such as baiting stations, and they have created safe zones for amphibian translocations. These zones are kept free of predators and pollution, and give amphibians diverse habitats to thrive in. The clean, pollution-free zones are especially important for frogs because they absorb chemicals through their skin. Previous translocations are probably one reason why frog populations had increased between 2013-2017.

You can help preserve NZ’s biodiversity! Bin your rubbish so it doesn’t end up in amphibians’ habitats. Think about your waste – including what ends up in the waterways. Plant native bushes and trees for NZ’s native animals. Finally, report to DOC if you spot any native NZ amphibians. And maybe it will be humans taking the leap to save our frogs.

Figure 3: Maud Island frog. Credit: Sabine Bernert.5 Image description: a small dark green frog with golden-flecked eyes and body. Its pupils are circular rather than slit.

References

1  Collins, J., & Crump, M. (2009). Extinction in our times global amphibian decline. Oxford: Oxford University Press.

2 McCallum, M. (2007). Amphibian Decline or Extinction? Current Declines Dwarf Background Extinction Rate. Journal of Herpetology, 41(3), 483–491. https://doi.org/10.1670/0022-1511(2007)41[483:ADOECD]2.0.CO;2

3 Blaustein, A., & Wake, D. (1990). Declining amphibian populations: A global phenomenon? Trends in Ecology & Evolution, 5(7), 203–204. https://doi.org/10.1016/0169-5347(90)90129-2

4 Hocking, D., Babbitt, K. (2014). Amphibian contributions to ecosystems. Herpetological Conservation and Biology 9(1):1−17.

5 Department of Conservation. (n.d.). New Zealand frogs/pepeketua. Accessed 4 March 2020 from https://www.doc.govt.nz/nature/native-animals/reptiles-and-frogs/frogs-pepeketua/.

6 Burns, R., Bell, B., Haigh, A., Bishop, P., Easton, L., Wren, S., Germano, J., Hitchmough R., Rofle J., & Makan T. (2017). Conservation status of New Zealand amphibians. Department of Conservation. doi: https://ndhadeliver.natlib.govt.nz/delivery/DeliveryManagerServlet?dps_pid=IE37630651.

7 Bell, B., Carver, S., Mitchell, N., & Pledger, S. (2004). The recent decline of a New Zealand endemic: how and why did populations of Archey’s frog Leiopelma archeyi crash over 1996–2001? Biological Conservation, 120(2), 189–199.

8 Bell, B., Bishop, P. (2018). Status of decline and conservation of frogs in New Zealand. In Status of conservation and decline of amphibians: Australia, New Zealand, and Pacific Islands (pp. 185-199). CSIRO Publishing.

9 Egeter, B., Robertson, B., Bishop, P. (2015). A synthesis of direct evidence of predation on amphibians in New Zealand, in the context of global invasion biology. Herpetological Review, 2015, 46(4), 512–519.

10 Rebecca Reid. (2018). Conserving New Zealand’s smallest frog, one record breaking leap at a time. Accessed 7 April 2020 from https://www.aucklandzoo.co.nz/news/conserving-new-zealands-smallest-frog.