Bennett's tree kangaroos, one of Australia's most mysterious marsupials, have long eluded researchers. Our new study, published in Australian Mammalogy today, has achieved a breakthrough: using thermal drones to detect these rare animals with unprecedented efficiency.
Author
- Emmeline Norris
PhD Candidate, Conservation Biology, James Cook University
Tree kangaroos are found only in the tropical rainforests of Australia and New Guinea. Unlike their ground-dwelling relatives, they spend their lives in treetops, feeding on leaves and vines. Their dependence on rainforest trees makes them vulnerable to deforestation and climate change .
Alarmingly, 12 of the 14 species of tree kangaroos are listed as threatened. Yet we know little about their numbers or habits due to difficulties studying them in dense rainforest.
Our new findings mark a significant step forward, offering hope for improved conservation of these elusive, near-mythical creatures. Thermal drones, which detect animals by their body heat, may help to unravel the mysteries of tree kangaroos and guide efforts to protect them.
Rugged, dense rainforests
Bennett's tree kangaroos inhabit Australia's most rugged and densely vegetated rainforests north of the Daintree River in Far North Queensland. They rarely descend from their vine-covered treetop roosts, which can be up to 40 metres high.
Traditional survey methods like spotlighting (that is, methodically using flashlights) or handheld thermal cameras (using infrared sensors to detect warm bodies) often fail to detect tree kangaroos, as these tools are limited to what can be seen from the ground.
As a result, there have been no systematic surveys of Bennett's tree kangaroos. Population estimates rely on outdated observations and anecdotal evidence, leaving their conservation status unclear.
We need robust population estimates to detect shifting population trends and prevent population declines. This requires new monitoring methods to help us find these elusive animals.
Hotspots in the treetops
Thermal drones are just what they sound like - drones equipped with infrared cameras that detect heat signatures from the air.
Warm-blooded animals like tree kangaroos stand out against the cooler rainforest background, even when partially hidden by foliage. This technology offers a powerful advantage over traditional methods, allowing researchers to scan large areas from above and see past vegetation.
In our study, we conducted three drone flights at the Daintree Rainforest Observatory , Cape Tribulation, during the morning and evening.
To our surprise, we detected six Bennett's tree kangaroos in under an hour of flight time - an unprecedented result. These included a solitary animal, a pair, and a group of three, all consistent with known home range sizes for the species.
By comparison, traditional ground surveys often require several nights of survey effort to spot a single animal. The drones not only made detection easier but also allowed us to closely observe the animals' behaviour, such as feeding on specific plant species, without disturbing them.
Shedding light on a hidden species
Our findings suggest Bennett's tree kangaroos are thriving in Cape Tribulation's lowland rainforest.
While this is encouraging, further systematic surveys are needed to assess how population density varies with forest type, elevation and other factors.
Another intriguing discovery was the tree kangaroos' diet. Using the drone's colour zoom camera, we identified the vines and leaves they were eating. Mile-a-minute vine (Decalobanthus peltatus) and fire vine (Tetracera daemeliana) were popular choices on the menu.
These observations deepen our understanding of the species' habitat needs and could inform future conservation efforts.
Conservation research methods must prioritise minimising stress on wildlife. The tree kangaroos showed no signs of disturbance, continuing to forage after briefly pausing to look at the drone.
This non-invasive approach is a promising alternative to traditional methods, like radio tracking (where a tag is attached to the animal), which can disrupt natural behaviours .
Craning for a better view
Despite showing promise, drone-based wildlife monitoring has its challenges. Regulations require drone operators to maintain visual line of sight with their drone. This can be difficult in a rainforest due to the height and density of the canopy.
To overcome this, we remotely operated our drone from a 47-metre-high canopy crane designed for research. This extra height allowed us to maintain a clear view while surveying a larger area.
However, canopy cranes are rare - there's only one in tropical Australia. Expanding this approach will require alternative strategies, such as using mountaintops or canopy walkways as vantage points.
Our study is just the beginning. The next step is designing methods to estimate population densities more accurately - not only for Bennett's tree kangaroos but also other tree kangaroo species in the remote mountains of New Guinea. By identifying individual tree kangaroos based on their unique fur markings, we aim to also study their social structure and sex ratios.
Thermal drones have the potential to revolutionise conservation efforts for hard-to-study wildlife . They offer a powerful tool to monitor populations and guide management decisions.
For the rare and remarkable Bennett's tree kangaroo, this technology could make the difference between obscurity and security.
Emmeline Norris does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
