Abstract
The use of small unoccupied aircraft systems (UAS) for ecological studies and wildlife population assessments is increasing. These methods can provide significant benefits in terms of costs and reductions in human risk, but little is known if UAS-based approaches cause disturbance of animals during operations. To address this knowledge gap, we conducted a series of UAS flights at gray seal breeding colonies on Hay and Saddle Islands in Nova Scotia, Canada. Using a small fixed-wing UAS, we assessed both immediate and short-term effects of surveys using sequential image analysis and between-flight seal counts in ten, 50 m2 random quadrats at each colony. Counts of adult gray seals and young-of-the-year animals between first and second flights revealed no changes in abundance in quadrats (matched pair t-test p > 0.69) and slopes approaching 1 for linear regression comparisons (r2 > 0.80). Sequential image analysis revealed no changes in orientation or posture of imaged animals. We also assessed the acoustic properties of the small UAS in relation to low ambient noise conditions using sound equivalent level (Leq) measurements with a calibrated U-MIK 1 and a 1/3 octave band soundscape approach. The results of Leq measurements indicate that small fixed-wing UAS are quiet, with most energy above 160 Hz, and that levels across 1/3 octave bands do not greatly exceed ambient acoustic measurements in a quiet field during operations at standard survey altitudes. As such, this platform is unlikely to acoustically disturb gray seals at breeding colonies during population surveys. The results of the present study indicate that the effects of small fixed-wing UAS on gray seals at breeding colonies are negligible, and that fixed-wing UAS-based approaches should be considered amongst best practices for assessing gray seal colonies.
Highlights
The use of small unoccupied aircraft systems (UAS) for terrestrial commercial and research applications is wide-spread in ecological science and wildlife management (Anderson & Gaston, 2013; Linchant et al, 2015)
Surveys of seals were conducted during January 29 to February 2, 2015 at Hay Island and Saddle Island, two gray seal breeding locations in Nova Scotia, Canada (Fig. 1) as part of a larger projecting assessing the utility of UAS to assess abundance of seals (e.g., Hammill et al, 2017; Seymour et al, 2017b; Seymour et al, 2017a)
Considering the above, the present study reveals that small fixed-wing UAS are a good alternative to occupied aircraft in terms of reduced acoustic disturbance
Summary
The use of small unoccupied aircraft systems (UAS) for terrestrial commercial and research applications is wide-spread in ecological science and wildlife management (Anderson & Gaston, 2013; Linchant et al, 2015). These devices are used to assess agricultural performance through a combination of visible and multispectral imagery (Zhang & Kovacs, 2012). Small UAS are used to assess environmental compliance in mining operations and to study the terrestrial habitats and abundance of wildlife (Koh & Wich, 2012; Linchant et al, 2015). The use of UAS can, in some situations, overcome these constraints while presenting opportunities to reduce costs and risk (Linchant et al, 2015)
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