Abstract
Accurate counts of wild populations are essential to monitor change through time, but some techniques demand specialist surveyors and may result in unacceptable disturbance or inaccurate counts. Recent technological developments in unmanned aerial vehicles (UAVs) offer great potential for a range of survey and monitoring approaches. They literally offer a bird's‐eye view, but this increased power of observation presents the challenge of translating large amounts of imagery into accurate survey data. Seabirds, in particular, present the particular challenges of nesting in large, often inaccessible colonies that are difficult to view for ground observers, which are commonly susceptible to disturbance. We develop a protocol for carrying out UAV surveys of a breeding seabird colony (Lesser Black‐backed Gulls, Larus fuscus) and subsequent image processing to provide a semiautomated classification for counting the number of birds. Behavioral analysis of the gull colonies demonstrated that minimal disturbance occurred during UAV survey flights at an altitude of 15 m above ground level, which provided high‐resolution imagery for analysis. A protocol of best practice was developed using the expertise from both a UAV perspective and that of a dedicated observer. A GIS‐based semiautomated classification process successfully counted the gulls, with a mean agreement of 98% and a correlation of 99% with manual counts of imagery. We also propose a method to differentiate between the different gull species captured by our survey. Our UAV survey and analysis approach provide accurate counts (when comparing manual vs. semi‐automated counts taken from the UAV imagery) of a wild seabird population with minimal disturbance, with the potential to expand this to include species differentiation. The continued development of analytical and survey tools whilst minimizing the disturbance to wild populations is both key to unlocking the future of the rapid advances in UAV technology for ecological survey.
Highlights
If the population dynamics of wild animal populations are to be understood and effective conservation management to take place, accurate estimates of population size are essential
Following initial exploration of the utility of Unmanned aerial vehicles (UAVs) in wildlife monitoring (Hodgson & Koh, 2016; Jones, Pearlstine, & Percival, 2006; Mulero-Pazmany et al, 2017), a number of seabird colonies have been counted using this approach. This has typically involved the collection of images by UAV survey followed by manual image counting of the number of individuals, for example Black-headed Gulls, Chroicocephalus ridibundus (Sardà-Palomera et al, 2012) and Common Terns, Sterna hirundo (Chabot, Craik, & Bird, 2015), with 93%–96% accuracy compared to ground counts
We found no impact of UAV survey flights at 15 m on gull behavior: There was no significant difference in either the number of flights by gulls (Wilcoxon signed rank test: V = 17, p = 0.1682) or the number of hops within the colony (V = 24, p = 0.2661) between the period immediately prior to or during the UAV survey flights (Figure 6)
Summary
If the population dynamics of wild animal populations are to be understood and effective conservation management to take place, accurate estimates of population size are essential. Some species are challenging to survey, inhabiting inaccessible locations that are difficult to visit or to observe (e.g., cliff-nesting or colony- nesting seabirds) or are susceptible to disturbance by fieldworkers or recreational activity (Giese, 1996; Kerlinger et al, 2013; Schlacher, Nielsen, & Weston, 2013). Seabirds require predator-free breeding sites with access to open seas, which are often in large colonies in isolated locations such as oceanic islands or sea cliffs, which can make monitoring populations difficult. A range of monitoring protocols have been developed to manually survey different colony-nesting seabird species, but the challenges of access, viewing, and disturbance remain, especially for gull species (Larus spp.; Walsh et al, 1995)
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