Counting threatened mammals with drones

By on 3 December, 2019

Drone technology assists with the extensive survey effort undertaken on Faure Island. Per annum, AWC ecologists on Faure undertake 400 live trap nights, 500 scat and tracking plot nights, 50 bird surveys at 17 sites, 41 km of spotlighting transects and 15 vegetation surveys. Photo by Brad Leue/AWC.

Investment in thermal imaging and drone technology is improving the monitoring of reintroduced mammals on Australian Wildlife Conservancy’s (AWC’s) Faure Island Wildlife Sanctuary, a feral-free haven off the coast of Western Australia.

Part of the Shark Bay World Heritage Area, Faure Island Wildlife Sanctuary is completely free of feral herbivores and predators, and home to critically important populations of Burrowing Bettong (Bettongia lesueur), Banded Hare-wallaby (Lagostrophus fasciatus), Western Barred Bandicoot (Shark Bay Bandicoot) (Perameles bougainville) and Shark Bay Mouse (Pseudomys fieldi).

Faure’s population of the Burrowing Bettong (Boodie) is estimated to be around 20,000 animals, at least half the global population. AWC currently monitors populations of these species through regular spotlighting, trapping and track surveys.

Accurate population estimates and species abundance data are necessary to create effective conservation management strategies, plan for future translocations, and monitor animal health. However, the combination of dense vegetation, cryptic animals and difficulties trapping some species make precise estimates difficult.

Could technology could help overcome some of these issues?

To find out, AWC staff and Travis Marshall, from technology firm C4D Intel, travelled to Faure Island in June 2019. Trials began, using a drone and thermal imaging camera to monitor recently established mammals.

Using a DJI M210 Aircraft fitted with a FLIR XT2 dual thermal/RGB sensor, the team wanted to see if different species could be both detected and differentiated using thermal imagery.

They also wanted to see if the technology could enable a better understanding of the behaviour of some of the reintroduced species, specifically Burrowing Bettongs (Boodies).

AWC ecologists had long suspected that Boodies were introducing a bias to current population estimates by moving around; that they were possibly ‘following’ and ‘escorting’ the ecologists during spotlight surveys and therefore being counted more than once.

Drone thermal imagery demonstrates the difficulties of accurately counting and identifying the species of individual mammals. Photo by Brad Leue/AWC.

The thermal camera proved excellent at detecting mammals.

As suspected, the team found that Burrowing Bettongs tended to ‘investigate’ people as they walked through the bush, potentially biasing population estimates through double counting.

Preliminary results suggest the technology may be an effective tool for monitoring bandicoots; however, the limited resolution made it difficult to distinguish between Burrowing Bettongs and Banded Hare-wallabies, which are similarly sized macropods.

Initial estimates of population size from the drone footage were comparable to those generated from standard spotlight surveys, demonstrating that the latter remains an effective method for generating population estimates.

Part of the Shark Bay World Heritage Area, Faure Island Wildlife Sanctuary is completely free of feral herbivores and predators, and home to critically important populations of several threatened mammal species.

AWC acquired Faure Island in 1999, declaring it feral-free in 2002 and beginning a program of threatened mammal reintroductions. Today, Faure’s wild, self-sustaining mammals are vital source populations for reintroductions to the mainland, and critical for the future survival of each species.

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