You might think frogs never get enough water. Turns out, they can fare worse in floods than bushfires
- Written by Eli Bieri, PhD Student, Australian Museum; UNSW Sydney
Frogs need water. Almost all of the world’s 7,900 known frog species breed in fresh water. And when it rains, these amphibians erupt into a chorus of calls – croaks, trills, cheeps and bellows – to attract a mate.
So you would assume a flood represents a windfall for frogs, right? But our new research finds they can have too much of a good thing.
Climate change is fuelling extreme weather, so we examined the impact of bushfires and floods on Australian frogs. We were surprised to discover that, in some cases, floods may pose a greater threat to Australian frogs than fire. This challenges our assumptions about how climate change will affect frogs in the future.
In the winter of 2021, frogs across eastern Australia were mysteriously found dead in gardens, creeks and backyards. The Australian Museum got hundreds of concerned emails from members of the public. We were stumped at the cause of this mass die-off.
Clue to mass frog deaths
Frogs play a vital role in the natural world. They control insect populations and also act as food for countless other species. And frogs are an indicator for a healthy environment, so when they start dropping dead it’s very concerning.
Our team collected thousands of dead frog specimens to test them for disease, and worked with collaborators to look for pesticides and other chemicals that might be to blame. So far, we haven’t found the factor likely to be responsible. Now, four years later, we have another clue.
In our search for answers, we wondered about recent extreme weather events in eastern Australia. The Black Summer bushfires in 2019–20 burned 24 million hectares, with an estimated three billion animals killed or displaced.
These years of fire and drought were immediately followed by record-breaking La Niña-driven rainfall and floods in 2021 and 2022. In the wake of these extraordinary climatic events, we asked: how do bushfires and floods impact frogs? Intuition told us fires would be a bigger threat to animals with such an affinity for water, but this assumption hadn’t been tested.
Thousands of helpers
Studying the effects of extreme weather is notoriously difficult, due to the unpredictable nature of natural disasters. Scientists often lack the critical baseline data they need. Without time to plan for disasters, we frequently can’t mobilise quickly enough to capture the immediate after-effects of the event either, particularly across vast tracts of land.
However, tens of thousands of people across Australia use the Australian Museum’s free FrogID app to record calling frogs. So we had access to a database of call recordings from before and after the fires and floods in NSW. By examining relative frog species “richness” – the number of frog species calling at once in recordings – we could compare how frogs responded.
Contrary to what you might expect, the number of frog species remained stable in burnt areas after the fires. This is actually in line with previous research by our team that documented the impressive short-term persistence of many frog species after the black summer bushfires.
Although good news for frogs, the long-term consequences of fires remain unknown, particularly for rainforest frog species that are not well represented in the FrogID dataset. Ongoing monitoring will be needed to track this over time.
Using the FrogID app to record frog calls at a burnt site in NSW.
Jodi Rowley, CC BY-ND
Too much water
The real surprise in our research was the impact of floods. It appears it is possible for frogs to have too much of a good thing when it comes to water. Frog species richness was significantly lower in flooded areas after the floods.
The most obvious responsible factor is floodwaters washing away frogs, including their eggs and tadpoles, and destroying sensitive frog breeding habitats. It’s also possible that floodwaters spread chemicals: a third of the dead frogs we tested after the mass frog deaths contained traces of pesticides.
The waterlogged habitats left in the wake of floods may have also created favourable conditions for the spread of the chytrid fungus. This pathogen is responsible for the devastating infectious disease chytridiomycosis. This affects the skin of amphibians, leading to symptoms like lethargy and excessive skin shedding. It causes mass mortalities and extinctions in populations worldwide.
A future of fires and floods
In a volatile Australian climate, we can expect more frequent and severe bushfires and floods.
This new research highlights the need for ongoing monitoring across Australia to track how frogs respond to increasingly extreme weather. With help from citizen scientists, we will be able to detect and respond to emerging threats whether they come in the form of fire, flood or fungus.
Most of Australia’s species have evolved alongside extreme weather. But the frequency and intensity of modern climate catastrophes are testing their resilience: they may not respond in the ways we expect.
In this rapidly changing world, gathering data on how our wildlife copes is essential. Citizen science projects like FrogID are vital in monitoring and managing Australia’s biodiversity into the future.
Authors: Eli Bieri, PhD Student, Australian Museum; UNSW Sydney
