Fighting the flames – how did frogs fare after the Black Summer bushfires?

FrogID citizen science data collected before and after the bushfires shows where frog populations persisted and where they might need our help.

Fire is not always a bad thing. In fact, it’s important for many Australian species to complete their life cycles, such as Banksias, which rely upon the extreme heat from fires to open their seed pods. Or even pink flannel flowers, which we saw only come to bloom once smoke and ash had covered the ground. However, as climate change rapidly increases, we are seeing fire become more severe, and with more catastrophic effects. The 2019/2020 Black Summer bushfires were an example, making it paramount to understand how species are responding to these more intense fires, especially those already under threat and in decline.

Unfortunately, one group of animals that is in rapid decline globally are frogs. In fact, over 40% of amphibians worldwide are threatened with extinction. Understanding how they respond to major environmental disturbances is crucial to their ongoing conservation.

But how do we find out how a frog species responds to fire? The best way to do that is to measure how a particular species is doing before fire and then compare that with how they are faring afterwards. But this is not always a straightforward task. Environmental disturbances like fire can be unpredictable. So, whilst it is usually easy to collect data after an environmental disturbance, we don’t always have access to records before the disturbance for comparison. However, citizen science data – like FrogID, eBird, or iNaturalist - has begun to change this, providing scientists with data they likely would not have been able to collect alone.

This is where the FrogID dataset proved invaluable. This dataset is based upon people across Australia recording frog calls with the FrogID app and, since November 2017, has gathered over one million frog records. As a result, we have frog occurrence records from across the areas burnt in the Black Summer bushfire, providing us with almost two years of ‘before’ data. And thanks to FrogID users from across the fire-zones, we had frog occurrence data within days after a fire had passed.To undersand how frogs respond to those devastating fires, we combined thousands of FrogID records with remotely-sensed (satellite) data revealing where and when a fire occurred, and how severe it was.

Remarkably, we found that while some areas were negatively impacted by fire, with a reduced number of frog species, some areas had the same or even a higher number of frog species after fire! The severity of the fire didn’t seem to have much influence on species richness. The reason for this varied response is unclear, but it is possible that the high rainfall of late 2020 (thanks to La Niña) meant that there were many more opportunities for frogs to breed after the fires - especially compared to the dry conditions prior. Additionally, the rainfall may have led to vegetation growing back quickly and more food resources, tempting some frog species to move into a nicer neighbouring area, where the grass is greener...literally. Perhaps in the areas where we saw frog species decline after fire, resources were not so plentiful.

While this is promising news, it’s important to note that range-restricted and rare frog species had fewer records, so we need more data to better understand their responses. It will also be crucial to continue monitoring our frog populations for any longer term implications.

Overall, thanks to the help of FrogID users, we are now able to better understand how frogs responded to the Black Summer bushfires in the two years after the fires and how to better conserve our frog species. Knowing which areas saw declines in frog species richness (and which areas didn’t) helps us focus our conservation efforts. So, when you’re next outside and hear a frog, please record it for the FrogID project. Every recording helps!

Britt Mitchell, PhD Candidate, Herpetology, Australian Museum Research Institute. Centre for Ecosystem Science, School of BEES, UNSW Sydney.