Real-time drone derived thermal imagery outperforms traditional survey methods for an arboreal forest mammal.

Ryan R Witt,Shelby A Ryan,Bob Denholm,John Clulow,Neil R Jordan,Chad T Beranek,Lachlan G Howell,Adam Roff,Mathew S Crowther

doi:10.1371/journal.pone.0242204

Abstract

Koalas (Phascolarctos cinereus) are cryptic and currently face regional extinction. The direct detection (physical sighting) of individuals is required to improve conservation management strategies. We provide a comparative assessment of three survey methods for the direct detection of koalas: systematic spotlighting (Spotlight), remotely piloted aircraft system thermal imaging (RPAS), and the refined diurnal radial search component of the spot assessment technique (SAT). Each survey method was repeated on the same morning with independent observers (03:00-12:00 hrs) for a total of 10 survey occasions at sites with fixed boundaries (28-76 ha) in Port Stephens (n = 6) and Gilead (n = 1) in New South Wales between May and July 2019. Koalas were directly detected on 22 occasions during 7 of 10 comparative surveys (Spotlight: n = 7; RPAS: n = 14; and SAT: n = 1), for a total of 12 unique individuals (Spotlight: n = 4; RPAS: n = 11; SAT: n = 1). In 3 of 10 comparative surveys no koalas were detected. Detection probability was 38.9 ± 20.03% for Spotlight, 83.3 ± 11.39% for RPAS and 4.2 ± 4.17% for SAT. Effective detectability per site was 1 ± 0.44 koalas per 6.75 ± 1.03 hrs for Spotlight (1 koala per 6.75 hrs), 2 ± 0.38 koalas per 4.35 ± 0.28 hrs for RPAS (1 koala per 2.18 hrs) and 0.14 ± 0.14 per 6.20 ± 0.93 hrs for SAT (1 koala per 43.39 hrs). RPAS thermal imaging technology appears to offer an efficient method to directly survey koalas comparative to Spotlight and SAT and has potential as a valuable conservation tool to inform on-ground management of declining koala populations.

Highlights

The koala (Phascolarctos cinereus) is a vulnerable cryptic, and mostly nocturnal, arboreal marsupial that often occurs in low densities, and can be laborious and costly to detect in the wild [1,2,3]
The results of our study show that remotely piloted aircraft system thermal imaging (RPAS) coupled with thermal imaging cameras are a promising efficient and effective alternative method to systematic spotlighting and the spot assessment technique (SAT) for detecting koalas and estimating density at low density sites in the winter period
We highlight the potential application of RPAS to garner new insights into koala behaviour, movement, and tree utilisation preferences

Summary

Introduction

The koala (Phascolarctos cinereus) is a vulnerable cryptic, and mostly nocturnal, arboreal marsupial that often occurs in low densities, and can be laborious and costly to detect in the wild [1,2,3]. The surviving koala populations endemic to New South Wales (NSW) have been

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