Short Communication |
Corresponding author: Lindsay A. R. Lalach ( lindsay.lalach@gmail.com ) Academic editor: Francisco Bonet
© 2023 Lindsay A. R. Lalach, David W. Bradley, Douglas F. Bertram, Louise K. Blight.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Lalach LAR, Bradley DW, Bertram DF, Blight LK (2023) Using drone imagery to obtain population data of colony-nesting seabirds to support Canada’s transition to the global Key Biodiversity Areas program. Nature Conservation 51: 155-166. https://doi.org/10.3897/natureconservation.51.96366
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Identifying of global or national biodiversity ‘hotspots’ has proven important for focusing and prioritizing conservation efforts worldwide. Canada has nearly 600 Important Bird and Biodiversity Areas (IBAs) identified by quantitative criteria to help guide avian conservation and management. Marine IBAs capture critical waterbird habitats such as nesting colonies, foraging sites, and staging areas. However, due to their remote locations, many lack recent population counts. Canada has begun transitioning IBAs into the global Key Biodiversity Areas (KBA) program; KBAs identify areas that are important for the persistence of biodiversity and encompass a wider scope of unique, rare, or vulnerable taxa. Assessing whether IBAs qualify as KBAs requires current data – as will future efforts to manage these biologically important sites. We conducted a pilot study in the Chain Islets and Great Chain Island IBA, in British Columbia, to assess the effectiveness of using drones to census surface-nesting seabirds in an IBA context. This IBA was originally designated for supporting a globally significant breeding colony of Glaucous-winged Gulls (Larus glaucescens). Total nest counts derived from orthomosaic imagery (1012 nesting pairs) show that this site now falls below the Global and National IBA designation criterion threshold, a finding consistent with regional declines in the species. Our trial successfully demonstrates a flexible and low cost approach to obtaining population data at an ecologically sensitive KBA site. We explore how drones will be a useful tool to assess and monitor species and habitats within remote, data-deficient IBAs, particularly during the transition to KBAs.
conservation, Important Bird and Biodiversity Areas (IBAs), population data
Important Bird and Biodiversity Areas (IBAs) are sites that contain a recurring presence of one or more regionally or globally threatened species (
The International Union for Conservation of Nature (IUCN) developed a process to identify Key Biodiversity Areas (KBAs) that was released in 2016; this conservation tool aims to identify sites that are important for the persistence of biodiversity and encompasses all taxa, as well as ecosystems in the assessment process. The criteria and thresholds for assessments of KBAs builds on the approach of the IBA program and other conservation framework tools, while bringing in other criteria based on vulnerability and irreplaceability (
As the world’s second-largest nation (9.98 million square kilometres), Canada lacks the biodiversity of smaller tropical countries, but has many areas of critical importance for aspects of temperate biodiversity. There are currently 581 sites identified as IBAs throughout the country. Approximately 64% of these IBAs are considered data deficient (
As with other nations, a high proportion (approximately 75%) of Canadian data deficient IBA sites are coastal and marine. Monitoring seabird colonies through field surveying is often expensive, difficult, and dangerous, and will invariably cause disturbance to nesting birds (
In this study, we used RPAS technology to estimate an IBA population count of a colonial-nesting seabird, the Glaucous-winged Gull (Larus glaucescens). Our objectives were to support the IBA program’s evolution to a KBA-based initiative; to explore the overall feasibility of using drone-based applications to obtain reliable IBA or KBA data; and to assess the current status of a nationally important seabird colony. This study location has historically supported one of Pacific Canada’s largest breeding colonies of Glaucous-winged Gulls, as well as migratory aggregations of as many as 2000 Brandt’s Cormorants (Urile penicillatus) in the area. For this reason, it was categorised as an A4i IBA and D1 KBA site, one which is “known or thought to hold 1% or more of a biogeographic population of a congregatory waterbird species on a regular basis” (
Our study took place at the Chain Islets and Great Chain Island IBA, a cluster of small islets and rocky outcrops along the marine coastline south of the City of Victoria in the Strait of Juan de Fuca (48.42°N, 123.28°W), British Columbia (Fig.
RPAS flight operations and protocol were selected to be consistent with a previous study in the region (
Flights were pre-programmed through drone mapping software (DroneDeploy, www.dronedeploy.com) to run single straight-line paths across the colony, offset to achieve consistent sidelap and followed by a return to the stationary vessel. Due to strong tidal currents in the region, the vessel motored in place instead of dropping anchor, with all vessel operations occurring outside the Ecological Reserve boundary, approximately 650 metres from Great Chain Island; this distance was well beyond the 100 m launch distance recommended by
Image capture was via a 28 mm lens on auto-exposure mode, certain flight specifics such as speed over ground and photo intervals were set by front-lap and side-lap requirements within the drone software. As flight altitudes and topography were variable throughout the six flights, ground sample distance (GSD) also varied. GSD ranged from 1.41 cm/pixel at 60 meters altitude to 2.11 cm/pixel at 90 meters. Drone flights were operated using one pilot and one visual observer, along with two additional observers monitoring the colony for any evidence of disturbance to nesting gulls during drone operations.
We used photogrammetry software to process drone flight images and create orthomosaics of the study area. Clear weather on the day of the flight generally created optimal light conditions for subsequent visual assessment of the orthomosaic imagery. However, solar glare on the less-vegetated small islets (approx. 33% of the colony) rendered a subset of the images overexposed; these islets were excluded from subsequent analysis. Orthomosaics of Great Chain were enlarged and visually scrutinised on-screen for occupied gull nests; these were readily apparent as the white and pale grey plumage of an incubating gull contrasts strongly with its background of rock and vegetation, and its posture is distinctive (Fig.
We conducted six flights capturing the entire IBA in 537 raw images. In the orthomosaic of Great Chain Island (Fig.
At all flight altitudes, no reaction was observed from nesting gulls during drone overflights, with the only alarm-calling or flushing by gulls observed when a single Bald Eagle (Haliaeetus leucocephalus), a gull predator, flew low over the colony on one occasion. No other seabird species were detected through the imagery analysis. The only other vertebrate species observed remotely on land was Harbour Seal (Phoca vitulina).
Our study successfully demonstrated an approach to using RPAS to survey and evaluate the population status of a colonial seabird at an ecologically sensitive and difficult-to-access site, in the context of monitoring an existing Important Bird and Biodiversity Area. The area overflown during the flights is natural, open rocky topography which generally creates an ideal setting for this type of analysis. The imagery captured from the flights was sufficient to analyze the large island within the IBA, however, some of the smaller rocky islets with little vegetation proved difficult to assess due to the high sun glare off the rocks and therefore were excluded from this trial. However, we were able to make use of previous surveys to estimate the nest counts for this minor part of the colony. Our project budget did not extend to extensive post-processing work, but we suggest that under similar conditions it might be possible to adjust exposure on each image prior to stitching the orthomosaic together to allow for a clearer visual of overexposed tiles. Alternatively, for rocky seabird colonies on light-coloured and/or guano-coated rocky substrate, drone surveys might best be scheduled for overcast days. The smaller islets within the IBA were not counted during this study, however with the addition of a 33% count of 464 nests (928 individuals), the total population of 1476 nests (2952 individuals) still would not qualify the site under the existing KBA thresholds.
Our count results were similar to ground-based survey data collected a decade earlier (
Canada is one of the first countries globally to transition IBAs to the KBA program. Two main challenges identified in the program crosswalk relating to survey data are data age and repeatability (Birds Canada, pers. comm.). “Lack of population data” was listed as a key methodological issue in six out of seven regions in an early assessment of KBA progress globally (
Though the use of RPAS technology has rapidly increased, gaps remain in establishing best practices for surveying sensitive species (
Drone surveying can not only assist in the establishment of KBAs but can provide critical population and habitat monitoring which can indicate habitat loss or degradation. It is evident that climate change will continue to pose stressors that may lead to fluctuations in biodiversity, potentially impacting elements for which a conservation site was initially designated (
While our study only used RPAS to obtain a viable count of breeding gulls, the imagery could be used to indicate the area of occupancy, the extent of suitable habitat, and the range of such habitat for this and other species; these are all metrics that are considered acceptable to assess qualifying KBA sites (
Obtaining updated population data is critical to understanding change and detecting risks to biodiversity. Drones provide the opportunity to significantly advance our understanding of environmental changes, especially within remote environments. The results of this study add to growing literature showing the effective use of drones in surveying surface-nesting birds in natural, hard-to-access settings. In a rapidly changing world where biodiversity continues to decline, obtaining accurate inventory data to capture that change remains a logistical challenge for many IBAs (
We would like to thank Alexandra King for creation of the map figure, Environment and Climate Change Canada Wildlife Research Division and Canadian Wildlife Service for funding the drone surveys, as well as Captain Bruce Evans and Fishing Vessel Misty Lady and visual observer Brian Badesso. We would also like to thank Geoff Mullins as the drone pilot for this survey and InDro Robotics for UAV-related support.
The authors have declared that no competing interests exist.