Tree kangaroos, which live high up in the tall rainforest trees of New Guinea and Australia, are usually very hard to spot from the ground. But thermal drones, which detect animals from their body heat, can help find these animals quickly, a new study has found.
In November 2024, Emmeline Norris, a Ph.D. student at James Cook University in Australia and the study’s lead author, was flying thermal drones from atop a 47-meter (154-feet) crane located in Daintree Rainforest Observatory, a research station run by the university in the Cape Tribulation rainforests.
Norris was opportunistically searching for spectacled flying foxes, the focus of her Ph.D. But about 20 minutes into the first flight, she spotted two Bennett’s tree kangaroos (Dendrolagusbennettianus): one perched atop the canopy, and one below, eating some vines. The next morning, her drones revealed four more individuals.
“It kind of blew my mind because I’d never seen them before in the wild,” Norris told Mongabay by phone.
In all, the thermal drones detected six Bennett’s tree kangaroos across 17 hectares (42 acres) of the forest, without seemingly disturbing them.
“It’s very impressive and shows the value of the methodology,” John Kanowski, chief science officer at the Australian Wildlife Conservancy, who wasn’t involved in the study, told Mongabay by email. “The density at the site is comparable with densities reported for Lumholtz’s tree-kangaroo.”
Of the 14 known species of tree kangaroos, 12 are found in New Guinea, and two — Lumholtz’s (D. lumholtzi) and Bennett’s tree kangaroos — live in Australia.
Researchers have traditionally surveyed tree kangaroos from the ground using either spotlighting — shining a flashlight into a tree canopy to spot a kangaroo’s bright red eye shine — or by using handheld thermal cameras. However, spotlighting only works if the animal is looking at the flashlight, and thermal cameras only work when the kangaroos are low in the trees, Norris said.
Lumholtz’s tree kangaroo lives in the rainforests of the Atherton Tablelands, where logging and agricultural activities have created roads and tracks, making the forest more accessible and sightings using traditional methods easier. By contrast, Bennett’s tree kangaroo’s patterns of distribution and abundance are poorly known because it largely lives in intact forests, Kanowski said. Since thermal drones can fly over the 40-m (130-ft) intact tree canopy, they could be useful for full-scale surveys of the species.
Kanowski added the drones could also be tested on Lumholtz’s tree kangaroos, since previous studies were based on spotlighting, which may have underestimated the species’ densities and populations.
However, there’s one challenge: the study used a tall crane to fly the thermal drones at the height needed, but there’s only one such crane in the Australian rainforest.
Norris said that for future population surveys, they’re considering flying from nearby mountaintops or buildings. “So, there are ways around it.”
Banner image: Bennett’s tree kangaroos spotted by thermal drones: color image (left), thermal image (right). Images courtesy of Emmeline Norris.
