Lessons learned from surveying Galápagos marine iguanas using drones.

Abstract

BACKGROUND Monitoring wildlife in remote areas is a key challenge in conservation, with traditional methods proving increasingly inadequate in the face of accelerating biodiversity loss. Uncrewed Aerial Vehicles (UAVs) or drones help bridge data gaps, but methods require careful development and validation to ensure protocols are appropriate, accessible, reproducible, and generate reliable data. Herein, we develop detailed UAV-based protocols for surveying the endangered marine iguana (Amblyrhynchus cristatus), a lizard that is endemic to the coastlines of the Galápagos Islands, Ecuador. We outline steps from image collection and processing, through locating and counting animals, before validating results against traditional methods. RESULTS We find that UAV-based surveys outperform traditional ground-based surveys in terms of count reliability and effort in the field in different types of terrain and various population densities. Moreover, we show that consumer-level drones can be used effectively - even by newly trained pilots - and describe a standardised manual flying protocol that mimics automated flying whilst maintaining flexibility in the field. Finally, we recommend the use of orthomosaics (geometrically corrected, high-resolution aerial image maps) for surveys on flat terrains and 3D models (digital representations of the surface in three dimensions) for cliffs and compare several common image-processing platforms in terms of success to reconstruct marine iguanas. CONCLUSION Our protocols advance the effective monitoring of Galápagos marine iguanas. Whilst they were specifically developed for this species, we postulate that these could be applicable for other species across the archipelago, or in coastal and open landscapes worldwide.