Smartphone LIDAR can measure tree cavity dimensions for wildlife studies

Abstract

ABSTRACTRemote sensing technologies are increasingly able to measure environmental characteristics important for wildlife, but remain limited in measuring small‐scale structures like tree cavities. Tree cavities are essential structures in many systems, including use for breeding and roosting by multiple animal species that vary in size. However, obtaining cavity dimensions directly is often difficult, dangerous, or impossible. During September–October 2017 at the University of Idaho Experimental Nursery in Moscow (ID, USA), we tested a handheld Light Detection and Ranging (LIDAR) device that interfaces with smartphones and tablets called Spike® by IkeGPS (Wellington, New Zealand) to determine whether it could be used to remotely measure tree‐cavity entrance dimensions. The Spike laser range‐finding device pairs with a mobile app to allow users to photograph a target (i.e., a tree cavity) on their phone or tablet and measure dimensions of that target onscreen. We designed an experiment to test the accuracy of Spike across 4 cavity entrance sizes ranging from 8.25 cm2 to 80.11 cm2, based on average cavity dimensions of Pacific Northwest woodpecker (Picidae) species. We varied height of target off the ground, obliqueness of the viewing angle (i.e., offset from target azimuth), and distance from target. Correlations between Spike measurements and cavity dimensions were high (r > 0.91 across 3 dimensions; n = 294). Measurement error for both vertical and horizontal diameters of cavity entrances was <1 cm on average. Accuracy was most influenced by taking photos from a large oblique viewing angle, high target height, and large distance from the target combined, based on results from generalized linear models. Spike proved to be a low‐cost, portable technology that can noninvasively measure structures that are small and difficult to access. Because of the ease with which it can be used, handheld LIDAR likely has potential future applications in wildlife research as well as citizen science education and outreach efforts. © 2019 The Wildlife Society.