Population census of a large Common tern colony with a small unmanned aircraft

• Main Authors: Chabot, Dominique, Craik, Shawn R., Bird, David M.
• Format: Dataset
• Language: unknown
• Published: figshare 2015
• Subjects: Environmental Science; Ecology; FOS Biological sciences; Common tern; Sterna hirundo
• Online Access: https://dx.doi.org/10.6084/m9.figshare.1317529.v5; https://figshare.com/articles/dataset/Population_census_of_a_large_Common_tern_colony_with_a_small_unmanned_aircraft/1317529/5

Abstract: Small unmanned aircraft systems (UAS) may be useful for conducting high-precision, low-disturbance waterbird surveys, but limited data exist on their effectiveness. We evaluated the capacity of a small UAS to census a large (>6,000 nests) coastal Common tern (Sterna hirundo) colony of which ground surveys are particularly disruptive and time-consuming. We compared aerial photographic tern counts to ground nest counts in 45 plots (5-m radius) throughout the colony at three intervals over a nine-day period in order to identify sources of variation and establish a coefficient to estimate nest numbers from UAS surveys. We also compared a full colony ground count to full counts from two UAS surveys conducted the following day. Finally, we compared colony disturbance levels over the course of UAS flights to matched control periods. Linear regressions between aerial and ground counts in plots had very strong correlations in all three comparison periods (R2 = 0.972-0.989, P < 0.001) and regression coefficients ranged from 0.928-0.977 terns/nest. Full colony aerial counts were 93.6% and 94.0%, respectively, of the ground count. Varying visibility of terns with ground cover, weather conditions and image quality, and changing nest attendance rates throughout incubation were likely sources of variation in aerial detection rates. Optimally timed UAS surveys of Common tern colonies following our method should yield population estimates in the 93-96% range of ground counts. Although the terns were initially disturbed by the UAS flying overhead, they rapidly habituated to it. Overall, we found no evidence of sustained disturbance to the colony by the UAS. We encourage colonial waterbird researchers and managers to consider taking advantage of this burgeoning technology. About the data: Raw aerial photos were captured in JPEG format by a Canon Powershot S90 10-megapixel camera mounted on an Aerial Insight AI-Multi electric fixed-wing UAS. Overlapping photos of each of the two islands comprising the tern colony were then mosaicked using the PTGui panoramic stitching software. Photomosaics were then imported into ArcGIS and georeferenced with ground control points collected with a Trimble Pathfinder GPS at a series of yellow or orange plastic cones (visible in the imagery) marking the centre of plots in which ground nest counts were compared to aerial tern counts. Overall disturbance levels on each of the two islands were scored on a scale of 0–2 from a distance by an observer at 30-second intervals throughout UAS flights as well as "matched" control periods starting 10 minutes following landing. For more information about this research or the data, please contact: [e-mail]