Did you know that individual frogs have distinct accents? That’s right, while all frog species have unique calls, there’s often a difference in the calls of individuals within a species too.
“But while we’re aware of the variation, we don’t really know why they can vary so much,” explains Grace Gillard, lead author of a new study in the Journal of Zoology that used large-scale data from citizen scientists to address this question.
They analysed the calls of nearly 700 banjo frogs recorded by citizen scientists as part of the FrogID project and found that variation in frog calls was not strongly linked to habitat structure.
“We were surprised by the results, because the link between habitat and variation in animal calls has quite a strong theoretical background,” says Gillard, who completed the project as part of her honours at the University of NSW in Sydney.
Instead, these new findings suggest that the evolution of banjo frog calls has instead been influenced by the interplay between a multitude of factors, such as noise from other animals, or anthropogenic noise, including wind and water.
“Importantly, we have shown that citizen science data provides a novel opportunity to examine important ecological theories across a huge spatial scale. And that the venue – a dense forest or an open plain – doesn’t matter for a banjo frog gig!”
Gillard and Dr Jodi Rowley, a herpetologist from UNSW’s Centre for Ecosystem Science, were investigating the acoustic adaptation hypothesis; animals that communicate acoustically adapt their vocalisations to local conditions to optimise their transmission through the environment.
Habitat can distort and reflect sound waves, so subtle changes in the pitch, duration, and rate at which an animal calls can counteract this to make sure the call reaches theintended audience.
They set out to test this theory for banjo frogs – a group of four closely related species widely distributed throughout Australia and within a wide range of habitats.
“These frogs are found in Western Australia, Tasmania and all along the east coast up to Far North Queensland. And so, if I were to go and try to analyse 700 calls in the field, well it would take at least 700 nights of recording calls, but also the time taken to travel between sites, and find the calling frogs, which is just not feasible,” says Gillard.
FrogID is an app developed by the Australian Museum where citizen scientists can record the calls of frogs from around the country.
“We had thousands of recordings of banjo frog calls at our fingertips. Using this data, we analysed nearly 700 banjo frog calls from across their entire range, covering an area of over 1.7 million km2, from Tasmania to Far North Queensland, and everywhere in between,” says Gillard.
Specifically, they were banjo frog advertisement calls – used by male frogs to attract potential mates to breeding habitats – which resemble a loud “bonk”.
They then paired this data with remote sensing imagery to get a measure of canopy cover and looked to see whether there was any correlation between the level of canopy cover and the acoustic parameters of each frog call.
Surprisingly, there wasn’t.
“Our findings have suggested that other factors may have a greater influence over the variation of Banjo frog calls. It’s likely going to be a combination of all different factors like more fine-scale features of the environment, acoustic competition from other frogs, and noise interference from wind, water, and other animals,” says Gillard.
“Next for this area of research, would be looking at different species of frogs. If we could do this research with different frog species with more complex calls, it might reveal more of a signal for habitat.”