Skip to main content
Dryad logo

Unmanned aerial vehicles as a useful tool for investigating animal movements - samples

Citation

Iwamoto, Masamichi; Nogami, Shonosuke; Ichinose, Tomohiro; Takeda, Keiji (2022), Unmanned aerial vehicles as a useful tool for investigating animal movements - samples, Dryad, Dataset, https://doi.org/10.5061/dryad.79cnp5hxc

Abstract

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.

Methods

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 Inspire 1 UAV equipped with a Zenmuse XT 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. Inspire 1 is a quadcopter UAV with DJI 1345T (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 DJI GO (application, SZ DJI Technology Co., Ltd) installed in an iPad Pro(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 (TB48, 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.

Funding

Odawara City Government

Yamagishi student project support program

Environmental Restoration and Conservation Agency, Award: JPMEERF19S20507

Shonan Fujisawa Campus Policy Research Support Organization