Frogs call at night, right?

Citizen scientists help us understand just how much Australian frogs call during the day.

Frogs call at night. Or do they? Using recordings of calling frogs submitted to the national citizen science project, FrogID, we take a closer look at just how much Australia’s frogs really do restrict their calling to night-time. Remarkably, about one in five recordings of calling frogs were during daylight hours, and some frog species were recorded more when the sun was out than at night! Our findings have important implications for when frog surveys can be carried out, and pose a whole new set of questions around just why some frog species call during the day.

Most frog species are nocturnal, meaning that they are more active at night. As a result, frog calls – the unique “love songs” made by male frogs to attract female frogs – tend to be heard at night, rather than during the day. But are Australian frogs also active in the day, and just how much do they call when the sun is up?

Collecting the kind of information necessary to answer the question is tough – Australia is large and there are more than 240 native frog species. Recording such a large number of frog species – either day or night – and across the continent, is a tough challenge! Luckily, thousands of citizen scientists across the country, armed with their phone and the FrogID app, have been recording calling frogs. Each recording includes the time and date, as well as geographic location, resulting in over hundreds of thousands of calls to help answer this question (and many others!).

Using over 160,000 FrogID records of 196 species, we found that almost two in five (39%) calling frogs were recorded between sunrise and sunset, and almost one in five (19% of all records) were really diurnal (calling at least 2 hours after sunrise and 2 hours before sunset).

Perhaps more surprisingly, FrogID recordings revealed that most of Australia’s frog species call during the day! At least to some extent. 71% of the frog species examined (140 of 196 species) were recorded during the day at least once. The frog with the highest percentage of call recordings made during the day was the Tasmanian Froglet (Crinia tasmaniensis), with 72% of all records of this species during the day. An additional 13 species had more than a quarter of their call recordings made during the day. However, some frogs were never recorded during the day. The Northern Ornate Nursery Frog (Cophixalus ornatus) and the Orange-thighed Tree Frog (Litoria xanthomera) were amongst these strictly nocturnal callers.

These results beg the question – why would a frog call during the day, when the likelihood of drying out in the sun, or being located by a predator is likely to be higher? Perhaps, if a frog is hiding in a moist habitat, the possible reward of finding a mate might make calling in the day worthwhile. Indeed, the three species with the highest proportion of diurnal calling are small (<2 cm body length) frog species that call from secretive positions in wet or moist microhabitats. Other species with relatively high rates of diurnal calls are known to produce toxins (e.g. the Brood Frogs (Pseudophryne)) probably reducing their predation risk. By calling during the day, frogs may also avoid having their calls drowned out by a chorus of other calling frogs.

Although most Australian frog species are more active at night, these findings also highlight the potential to survey for many frog species during the day as well. This is particularly important considering the large number of threatened frog species in Australia. Indeed, three of the top ten species in terms of their proportion of diurnal calling are threatened species (the Wallum Froglet (Crinia tinnula), the Red-crowned Toadlet (Pseudophryne australis) and the Green and Golden Bell Frog (Litoria aurea).

While these results are a fantastic insight into when frogs call, they are also an indication of when people are up and recording frogs. Not surprisingly, there are relatively few submissions in the early hours of the morning! The more recordings of frogs submitted, the clearer the frog calling times will be.

Recordings of calling frogs by citizen scientists across Australia has revealed widespread diurnal calling across a taxonomically, ecologically, and geographically diverse frog fauna. Thank you to every single person that has submitted a recording of a calling frog to the FrogID project, day or night. Please keep recording frogs, whatever time of day you hear them!

Dr Jodi Rowley, Curator, Amphibian & Reptile Conservation Biology, Australian Museum Research Institute & UNSW Sydney.

Dr Corey Callaghan, Centre for Ecosystem Science; School of Biological, Earth and Environmental Sciences; UNSW Sydney.

More information:

Callaghan, C.T. & Rowley, J.J.L. (2020). A continental assessment of diurnality in frog calling behaviour. Austral Ecology. https://doi.org/10.1111/aec.12959

Acknowledgements:

We thank the Citizen Science Grants of the Australian Government for providing funding for the FrogID project, the Impact Grants programme of IBM Australia for providing the resources to build the FrogID App, Bunnings Warehouse Australia, Fyna Foods, John T Reid Charitable Trusts, and other project partners and support for FrogID. We thank the thousands of citizen scientists who contribute to FrogID records, and the FrogID team, who validates submissions, thus creating the robust dataset which made this study possible.