186 O. R. Wearn et al.
traditional observationsmade by survey teams but we antici- pate they could be used on their own to survey gibbons (e.g. using line or point transects), assuming that imperfect detec- tion could be accounted for. There are both advantages and disadvantages to
UAV-assisted monitoring of the cao vit gibbon and other primate species. We found that the advantages in- clude the fact that observations (e.g. of group size and composition) were less biased because of the greater de- tection capabilities of thermal cameras compared to the human eye. In general, this is likely to be the case when species are cryptic and/or partially obscured by vegetation. Remote observations using the UAV could also be made of groups that would have otherwise been too far away for human observers to reach, providing more data. However, the initial equipment costs are considerable (e.g. in our case a total of USD 6,700 for one UAV, one controller and five batteries), pilots had to be trained to operate the UAV safely and effectively, and technological limitations constrained data collection (in particular the short battery life and requirement for suitable environ- mental conditions for both flying and effective use of the thermal camera). In common with other studies (Kays et al., 2019; Zhang et al., 2020), we noticed that the effect- iveness of the thermal camera was dependent on a suf- ficient temperature contrast between the target animals and their surroundings. We collected our data during a relatively cool period of the year (with ambient daytime temperatures typically 15–24 °C) and we expect that the thermal camera would be less useful during hotter periods of the year. Our study adds to a growing, albeit nascent, literature
demonstrating the effectiveness of drones for monitoring and studying primates and other threatened taxa (e.g. Hu et al., 2020; Oliveira-da-Costa et al., 2020; Piel et al., 2021). With further technological improvements, especially in battery life and thermal sensor resolution, we foresee an increasing role for UAV-based data collection in the monitoring and study of not just cao vit gibbons but a wide range of other cryptic and difficult-to-study species.
Acknowledgements Wethank the Gibbon Conservation Team and our government partners in Trung Khanh District and Cao Bang Province for their support in this work. Funding was provided by the Arcus Foundation, IUCN Save Our Species and Disney Conservation Fund.
Author contributions Study design, fieldwork, writing: ORW, HT-D, QKL, TDN; data analysis: ORW.
Conflicts of interest None.
Ethical standards This research abided by the Oryx guidelines on ethical standards. Flights were operated in accordance with regulations in Vietnam, under license from the Ministry of Defence.
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Oryx, 2024, 58(2), 183–186 © The Author(s), 2023. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605323000017
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