Remote, non‐invasive photogrammetry for measuring physical traits in wildlife

Abstract

AbstractMorphometric measurements in wildlife are essential data needed to link behaviour and ecology to life‐history traits. However, acquisition of such data, especially in large vertebrates, is a challenging and limiting aspect in many studies due to associated capture and handling. Ultimately, this prevents testing important hypotheses in wildlife ecology. We demonstrate how to overcome some of these challenges by improving the far‐reaching potential of photogrammetry for wildlife. We validate a methodology using photogrammetry to acquire measurements of complex, curvilinear, morphometric traits (deer antlers) at long range (up to 200 m), providing a methodological foundation for further application to numerous physical attributes and species. We calibrated and validated two different photogrammetric camera systems and applied long‐range photogrammetry to measure a suite of antler features from deer trophies positioned analogous to free‐living, wild deer. We also developed, validated and described an efficient correction protocol to overcome the complexity of three‐dimensional antler features. This complexity previously biased the acquisition of absolute measurements. Our measurement estimates were characterized by mean errors lower than 5% when compared to true sizes, with our correction protocol for antlers particularly effective and validated with independent antler sizes. Importantly, the estimated size rankings based on the true sizes were identical to the rankings estimated by photogrammetry in all cases. We measured antlers in free‐living, wild fallow deer as a field validation and demonstration, showing how we were able to collect physical trait measurements of 230 antlers without capture. This non‐invasive, remote and fast technique can provide valuable and accurate data allowing researchers to address new hypotheses by linking life‐history traits to wildlife ecology, behaviour and management.