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

Ryan R Witt; Chad T Beranek; Lachlan G Howell; Shelby A Ryan; John Clulow; Neil R Jordan; Bob Denholm; Adam Roff

doi:10.1371/journal.pone.0242204

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

PLoS One. 2020 Nov 16;15(11):e0242204. doi: 10.1371/journal.pone.0242204. eCollection 2020.

Authors

Ryan R Witt^{1

2}, Chad T Beranek^{1

2

3}, Lachlan G Howell^{1

2}, Shelby A Ryan^{1

2}, John Clulow^{1

2}, Neil R Jordan^{4

5}, Bob Denholm³, Adam Roff^{1

3}

Affiliations

¹ School of Environmental and Life Sciences, University of Newcastle, Callaghan, New South Wales, Australia.
² FAUNA Research Alliance, Kahibah, New South Wales, Australia.
³ Science Division, NSW Department of Planning, Industry and Environment, Newcastle, New South Wales, Australia.
⁴ Centre for Ecosystem Science, School of BEES, University of New South Wales (UNSW Sydney), Sydney, New South Wales, Australia.
⁵ Taronga Institute of Science and Learning, Taronga Conservation Society Australia, Taronga Western Plains Zoo, Dubbo, New South Wales, Australia.

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.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Aircraft*
Animals
Forests
Phascolarctidae / physiology*
Population Density*
Telemetry / methods

Grants and funding

This work was funded by Remote Sensing and Landscape Science, Science Division, NSW Department of Planning, Industry and Environment and the University of Newcastle Centre for Creative Industries. Follow-up spotlighting line transect surveys used to calculate f(0) as per S1 were funded by Taronga Conservation Society, Australia. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. The funders provided support in the form of salaries for authors [CTB, BD, NRJ, AR], but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the ‘author contributions’ section.