10,000 Hours Listening For Screaming Koalas
Mini-acoustic sensors reveal occupancy and threats to koalas Phascolarctos cinereus in private native forests (2021) Law et al., Journal of Applied Ecology, https://doi.org/10.1111/1365-2664.14099
Forests that lie on privately owned land make up a huge percentage of Australia’s native forests – over 23%. That’s 164 million hectares, a massive swathe of territory for Australia’s amazing endemic species to call home.
The problem is that because it’s private, it’s often difficult to survey. Which means there’s a huge chunk of an ecosystem that we have very little knowledge about. Sometimes this frustrates, but other times it breeds novel approaches to conservation.
This week’s authors wanted to survey native Australian forests, with one species in mind – the charismatic and oft-threatened koala. They took an approach which brought land-owners on board, and sent them audio recording equipment to register the presence of koalas, in an effort to figure out how many koalas made use of private forests.
What They Did
Spread across Australia’s privately owned forests, the researchers found just under a million hectares worth of land that they estimated to be suitable for koalas. They contacted the owners of said land and explained the project and its significance. Once the owners understood the concept and the work involved, they were sent ‘Audiomoths’ – small recording devices that can be attached to trees in koala habitat and record male koalas bellows during mating season (September to December).
Recording koala bellows isn’t that straightforward though, and many recordings had to be removed from the final results as heavy wind and rain made it difficult to determine what was making what noise.
Once koalas were identified, their presence was modelled against a range of different human impacts, including nearby roads and land clearance, and environmental variables like extent of vegetation and local fire severity.
Did You Know: Koala Extinction
Koalas are notoriously picky eaters, and many people know that they will only eat eucalyptus leaves. Yet it goes further, with some koalas only eating leaves from certain species of eucalyptus tree, having grown so accustomed to these species that their gut bacteria can’t tolerate anything else. It means that relocating koalas can be almost impossible, and that preserving their natural habitat is of the utmost importance (and benefits a huge range of other species).
What They Found
The survey resulted in almost 10,000 hours of recordings across 128 properties and three years. Over 1,600 bellows were recorded across 41% of all the sites surveyed.
The only variables which had an affect on koala presence were the proximity of sealed (paved) roads and the vegetation cover. The closer by a sealed road was, the less likely koalas were to show up. Heavily forested areas were also less likely to house koalas, whereas forest that was more fragmented by grassland and open woodland were better suited for them.
The study mentions early on that there are often differences between private and public forest, yet there’s no comparison here between the two. Using Audiomoths in public nature reserves would have made for a great comparison, particularly to check whether the environmental and human variables affected koalas in the same way. However the constraints here are financial ones, and I think the authors would agree that it’s more interesting the double the data for this particular experiment rather than double the Audiomoth budget and make a comparative study.
The environmental results here aren’t particularly interesting – koala’s habitat preferences are relatively well studied. What is a real positive is the success of the technique used, that of bringing private landowners on side and getting a wealth of data in return. An added bonus of a project like that is that as well as collecting data, you get the opportunity to share scientific knowledge and teach a group of the public about local wildlife.
Dr. Sam Perrin is a freshwater ecologist who completed his PhD at the Norwegian University of Science and Technology and is currently working as a climate data analyst at Ducky AS. You can read more about his research and the rest of the Ecology for the Masses writers here, see more of his work at Ecology for the Masses here, or follow him on Twitter here.