By Mahalia Booth-Remmers, Field Ecologist, Dr Laurence Berry, Senior Wildlife Ecologist and Georgia Volck, Senior Field Ecologist
Efficiently tracking reintroduced species and producing reliable estimates of population trends over time is fundamental to the planning, delivery and ongoing evaluation of AWC’s ambitious reintroduction program. Threatened mammal species can be difficult to monitor due to low population densities, nocturnal and cryptic behaviour, and the remoteness of remnant populations. Common monitoring approaches such as live trapping, spotlighting and remote camera trapping can be limited by animal detectability, observer effects or analytical assumptions that are difficult to satisfy. Using drones can address these limitations and presents a potentially more cost and time-effective method for monitoring wildlife. Investment in technology to improve the quality and accuracy of monitoring programs is a high strategic priority for AWC.
In 2019, AWC hired a commercial drone company C4D to conduct night flights of a drone-mounted infrared thermal imaging camera (thermal drone) over Faure Island to investigate the potential to monitor populations of reintroduced mammals. The trial showed promise, but flight duration and camera resolution limited routine application.
In June 2021, following improvements in drone and camera technology, AWC implemented a further trial to evaluate the feasibility of a thermal drone to estimate the population size of Greater Bilbies within the 480-hectare breeding area at Mallee Cliffs National Park in south–western NSW. The availability of new, compact, high-resolution thermal cameras increased the capacity to identify small ground-dwelling mammals from the air. For this work, AWC engaged contractor Beau Ricketts.
Thermal drone footage of a Bilby taken during trials at Scotia Wildlife Sanctuary. AWC
On five occasions, the thermal drone was flown over the same 24.8 kilometres (11 transects, each 200 metres apart), covering a total area of 61.8 hectares. The footage was reviewed by AWC ecologists and Bilby observations marked with high, moderate, or low confidence. These results were compared with estimates derived from a cage-trapping survey conducted within the breeding area involving 100 traps checked over a 4-night period. The resulting population estimates were similar: the mean population estimate produced from the thermal drone data was 123 (±32) and from the live-trapping data 118 (±28). These results suggest thermal drones have the potential to be an effective alternative method for surveying reintroduced mammals within fenced areas.
Future trials will repeat this work over larger areas with multiple reintroduced mammal species and compare the results against those derived from other common methods such as spotlighting. AWC has already undertaken a second trial at Scotia Wildlife Sanctuary in NSW over a much larger area and has plans to repeat this work on other AWC sanctuaries with reintroduction programs.
Radio tracking drones
In May 2021, AWC reintroduced Brushtail Possums both inside and outside the feral predator-free fenced area at Mt Gibson Wildlife Sanctuary in Western Australia’s Wheatbelt region. This was a landmark release, the first time a species was intentionally reintroduced outside the fenced area at Mt Gibson, in conjunction with a feral predator control program. The results from radio tracking demonstrated excellent survival of this species and several of the possums moved large distances – even up to 30 kilometres from their release sites. Tracking these animals with conventional handheld telemetry equipment was incredibly challenging, proving both labour and time-intensive. This year AWC plans to reintroduce the Chuditch (Western Quoll) to Mt Gibson, the tenth species for this reintroduction program that already sets the benchmark for rewilding efforts across the country. Chuditch will only be released outside the fenced safe haven and this species is expected to move even larger distances than the possums after release!
To assist with monitoring, AWC will use a radio tracking drone and software from the company Wildlife Drones to track collared Brushtail Possums and Chuditch across the sanctuary. Applying this novel technology will improve the field team’s ability to regularly track animals to an accurate location across Mt Gibson’s 132,000 hectares (large portions of which are inaccessible by track), reducing the time spent searching for missing animals and increasing the time spent recording important data on survival, dispersal and habitat use. This method of radio tracking involves sending the drone up to search a pre-determined area and recording a fix of the location for each animal/collar. This technology has the potential to significantly increase tracking efficiency across large areas and we look forward to reporting the results to you.
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