A Novel Method for Using Small Unoccupied Aerial Vehicles to Survey Wildlife Species and Model Their Density Distribution

Abstract

There is growing interest from research and conservation groups in the potential for using small unoccupied aerial vehicles (UAVs; <2 kg) to conduct wildlife surveys because they are affordable, easy to use, readily available and reliable. However, limitations such as short flight endurance, and in many situations, aviation regulations, have constrained the use of small UAVs in survey applications. Thus, there is a need to refine survey methods adapted to small UAVs that conform to standard operations within aviation law. We developed a novel survey approach based on a grid sampling design using two multirotor UAVs (Phantom 4 Pros) flying simultaneously, within visual line of sight, from our vessel base-station. We used this approach to assess the fine-scale distribution and abundance of dugongs (Dugong dugon) in the remote waters of the Pilbara, Western Australia during three field seasons across 2 years. We surveyed 64 non-overlapping survey cells in random order one or more times and obtained complete image coverage of each surveyed cell of our 31 km2 survey area. Our sampling design maximizes sampling effort while limiting survey time by surveying four cells, two at a time, from one location. Overall, we conducted 240 flights with up to 17 flights per day (mean = 14 flights per day) and could obtain complete coverage of up to 11.36 km2per day. A total of 149 dugongs were sighted within the 50,482 images which we manually reviewed. Spatially-explicit models of dugong density distribution (corrected for availability and perception bias) were produced using general additive models to identify areas more or less used by dugongs (range of corrected dugong densities across all field season = 0.002–1.79 dugongs per 0.04 km2). Dugong abundance estimates ranged from 47 individuals in June 2019 (CV = 0.17) to 103 individuals in May 2018 (CV = 0.36). Our method, which proved convincing in a real-word application by its feasibility, ease of implementation, and achievable surface coverage has the potential to be used in a wide range of applications from community-based local-scale surveys, to long-term repeated/intensive surveys, and impact assessments and environmental monitoring studies.

Long‐term persistence of large dugong groups in a conservation hotspot around Hawar Island, Kingdom of Bahrain

“…In addition, an important source of information was the structured interviews with key informants, and the possibility of inaccurate recollections of encounters due to failing memories cannot be discounted. Despite their large numbers, clumped dugong groups are often difficult to observe from the air (Preen, 1989; Pollock et al, 2006; Cleguer, 2015; Cleguer et al, 2021; Trotzuk et al, 2022). This is even more complex for boat‐based surveys that depend on surfacing individuals; dugongs resting or feeding underwater make accurately estimating group size a real challenge.…”

Increasing the accuracy and efficiency of wildlife census with unmanned aerial vehicles: a simulation study

“…Although this obviously impacts the time needed for surveying a given area, we suspect the requirement of photogrammetric approaches commonly applied on drone data as a reason for the chosen designs. Regulatory restrictions on flying beyond-line-of-sight might further have pushed researchers to embark on such a strategy, focusing on small areas around the takeoff location (Cleguer et al 2021). Early adopters of UAV technology included experimental approaches, such as feature (e.g.…”

“…Manned aerial surveys that cover a representative percentage of the total area currently still constitute the main approach to wildlife population surveys over large spatial scales, though unmanned aerial vehicles (UAVs) may efficiently and reliably fill prevalent shortcomings (Fust and Loos 2020). Despite current legal restrictions (Cleguer et al 2021), the merits of UAV-based surveys include its programmability, which allows surveying predefined complex survey patterns (Cabreira et al 2019), which might be necessary to ensure an even and constant area coverage probability, for example in highly heterogeneous landscapes. An even and constant area coverage probability can be achieved through adjustments of the layout of the flight transects (Strindberg and Buckland 2004).…”

“…Manned aerial surveys that cover a representative percentage of the total area currently still constitute the main approach to wildlife population surveys over large spatial scales, though unmanned aerial vehicles (UAVs) may efficiently and reliably fill prevalent shortcomings (Fust and Loos 2020). Despite current legal restrictions (Cleguer et al . 2021), the merits of UAV-based surveys include its programmability, which allows surveying predefined complex survey patterns (Cabreira et al .…”

Reduction of Species Identification Errors in Surveys of Marine Wildlife Abundance Utilising Unoccupied Aerial Vehicles (UAVs)

“…These versatile platforms offer high data quality and accessibility to remote environments [4][5][6]. In addition, their utility for abundance estimation has been demonstrated for various taxa, including elephants, marine mammals, sea turtles, sharks, jellyfish, and birds [7][8][9][10][11][12][13], yet most studies have relied on either raw counts or corrected indices without accounting for detection errors in the new type of data, i.e., digital imagery in place of direct human observations [14]. Nonetheless, evaluating the factors that influence animal detectability is a prerequisite for solid ecological inference and environmental conservation [15,16].…”