DOI: 10.5061/dryad.79cnp5hxc
title: Unmanned aerial vehicles as a useful tool for investigating animal movements - samples

description: Determining animal abundance is crucial for assessing the effectiveness of
 management measures against pest animals. Meanwhile, investigating animal
 movements has become important for conducting abundance estimations of
 unmarked animals since the random encounter model (REM) was published. REM
 is a camera-trapping method that derives animal density by using contact
 ratio between camera-traps and targeted animals that randomly move at a
 certain speed in a given area. However, it requires an independent value,
 which is animal speed. For investigating animal speed, camera-traps with
 video recording and GPS tagging are the commonly used tools. Unmanned
 aerial vehicles (UAVs) are currently used in wildlife monitoring to
 investigate the abundance of target species. It is evaluated as a tool
 that is non-invasive and suitable for surveys in inaccessible landscapes.
 Considering these characteristics, we regarded a distant survey using this
 technology as suitable for investigating animal movements. Therefore, we
 proposed a method for estimating animal movements using UAVs and conducted
 a case study that aimed to investigate wild boars' movements. We
 collected 11 video samples that successfully followed the movements of
 wild boars from 26 UAV flights in total, and the average speed of their
 movements derived from all the samples was 1.54 km/24 h. We found that
 issues can be improved, including species identification, video sample
 length, and animal behaviours or activity patterns. On the other hand, our
 method showed potential for applying to species with specific
 characteristics in their body size, shape or activity patterns. With
 improvements in the issues mentioned above, UAVs would become an
 alternative tool for investigating animal movements.
description: We surveyed 8 to 10 November
 in 2019, from
 21:00 to 5:00, to collect
 data on wild boar movements. The survey was conducted nocturnally with the
 intention of allowing the ambient temperature to drop and because wild
 boars were known to be nocturnal in Ishibashi
 district. An <em>Inspire</em>
 <em>1</em> UAV equipped with a <em>Zenmuse</em>
 <em>XT</em> thermal camera (FLIR Systems, Inc., Wilsonville,
 Oregon, United States) was flown manually in areas where wild boars were
 likely to be present. The weight of UAV, including the thermal camera,
 was 3,115 g. <em>Inspire 1</em> is a quadcopter UAV with
 <em>DJI 1345T</em> (SZ DJI Technology Co., Ltd) propellers.
 The diagonal dimension without the propellers in landing mode is 581 mm.
 Zenmuse XT is an uncooled Vox microbolometer with 640*512 resolution, 17
 μm pixel pitch, 13 mm focal length, and 7.5 to 13.5 μm spectral
 band. We used the<em> DJI GO</em>
 (application, SZ DJI
 Technology Co., Ltd)
 installed in an <em>iPad Pro</em>(Apple Inc., Cupertino,
 California, United States) as a screen to monitor the flight, which showed
 the image from the camera in real-time. For this reason, an internet
 connection was required during the survey. We prepared eight batteries
 (<em>TB48</em>, SZ DJI Technology Co., Ltd), but we had to charge the batteries while
 conducting the flights. We overcame this issue by carrying an emergency
 battery capable of 100 V AC output. We flew the UAV approximately 50 m from the
 ground. This was because we wanted to avoid disturbing the animals, and we
 were able to distinguish boars and other species according to their body
 size and shape. The data were collected as videos, and once we detected a
 boar, we flew the UAV right above it, ensuring that the boar was in the
 centre of the tablet’s screen. Then we let the UAV hover (until the UAV
 emitted a low-battery signal). To make it easier to calculate the
 distances from which the boars moved, we recorded the videos with the
 camera facing the ground perpendicularly, as if it were a fixed-point
 camera in the sky.