Testing Drones as a Tool for Surveying Lizards

Abstract

A lack of effective methods for sampling lizards in terrain that is inaccessible to human observers limits our knowledge of their ecology and conservation needs. Drones are increasingly being used in wildlife monitoring, but their potential use for surveying lizards has not been evaluated. We investigated: (1) the detectability of model lizards using a drone relative to a human observer, and (2) the response of four lizard species to an approaching drone in three habitat types. Model lizards placed in potential basking positions within a defined search area were detected by both the drone operator and human observer, but the probability of detection was lower with the drone. Jewelled geckos (Naultinus gemmeus) in shrubland and grand skinks (Oligosoma grande) in rocky habitats showed surprisingly little reaction to the approaching drone, enabling close approaches (means of 59 cm and 107 cm, respectively) and accurate species identification with photos taken by the drone camera. For highly patterned jewelled geckos, identification was also possible on an individual level. However, the drone was unsuccessful at detecting two alpine skink species in a near-vertical cliff habitat. Collectively, our results suggest that drones have potential as a tool for detecting small-bodied lizards in habitats inaccessible to human observers.

A pilot study to estimate the population size of endangered Galápagos marine iguanas using drones

“…Drones are now readily available, typically do not require high levels of specialist training to pilot, and give visual access to remote locations that are impossible to reach by other means. Several examples proving the efficacy of drone-based monitoring in a variety of habitats now exist, covering a range of terrestrial and marine species, such as crocodiles [ 8 ], sea turtles [ 9 ], lizards [ 10 ], sharks [ 11 ], and birds [ 12 , 13 ]. Crucially, drones offer a means by which to reach threatened and understudied species in inaccessible terrains, such as those living in remote island localities.…”

A bird’s-eye view: Evaluating drone imagery for the detection and monitoring of endangered and invasive day gecko species

“…2 C). Approach distances were unexpectedly short, even shorter than previously found in New Zealander lizards, with 33.8 cm in average for P. inexpectata versus approximately 59 cm for the Jewelled geckos Naultinus gemmeus and 107 cm for the grand skinks Oligosoma grande (Monks, Wills, and Knox, 2022). This allowed for short-distance photo taking and high-resolution imagery.…”

“…However, the use of drone imagery was highly complementary to the visual counts, since we detected additional individuals on Pandanus leaves in the canopy. We assume that the benefit of drone-based monitoring might become clearer in less accessible areas such as cliffs and shrublands and may outperform visual counts (Monks, Wills, and Knox, 2022; Varela-Jaramillo et al, 2023). Phelsuma inexpectata is distributed along the coastline, inhabiting steep slopes and cliffs.…”

“…Consequently, species living in complex habitats or with dynamic habitat use are poorly understood and their conservation becomes challenging. The development of novel cost-effective methods for cryptic or threatened species monitoring is a priority for their conservation (Monks, Wills, and Knox, 2022). Insular endemic species are particularly vulnerable to invasive alien species (IAS).…”

“…Novel methodologies such as computer assisted slow-speed road cruising (Jones et al, 2022) or camera-trapping (e.g., Roesch, Hansen, and Cole, 2021; Deso, Crouzet, and Bonnet, 2022) have already proven efficient. Drones have recently been used for the monitoring of endangered species (Landeo-Yauri et al, 2020; Varela-Jaramillo et al, 2023), including cryptic reptiles (Monks, Wills, and Knox, 2022), and have improved the detection of invasive reptile species living in the tree canopy (Aota et al, 2021).…”