Parallel‐laser photogrammetry to estimate body size in free‐ranging mammals

Abstract

ABSTRACT It is not always practical to hand‐measure body size of free‐ranging animals. In recent years, parallel‐laser photogrammetry has become increasingly common for obtaining remote estimates of body size. However, it is unknown how well this technique might capture variation in body size of curvilinear features or whether the distance between parallel‐laser calipers is altered when projected onto a curved surface. We describe a photogrammetric system that may be useful for obtaining body‐size measurements from unrestrained large mammals that permit approach. We tested the use of parallel‐laser photogrammetry to estimate the size of curvilinear features in domestic horses (Equus ferus caballus) and identified morphometrics that explained variation in body weight. Despite projecting the lasers onto a curved surface (the barrel of a horse), we achieved accurate photogrammetric estimates of linear hand‐measurements. The curvilinear hand‐measurements also showed strong correlations (R2 ≥ 0.996) with their respective linear photogrammetric estimates, and most photogrammetric estimates had high reliability. Using 3 variables of body size, photogrammetric estimates and hand‐measurements explained 86.0% and 96.2% of the variation in weight, respectively. © 2015 The Wildlife Society.

Keywords

• body size
• conformation
• Equus ferus caballus
• horse
• morphometrics
• parallel‐laser calipers