An Improved Technique for Obtaining Accurate and Precise Morphometric Data on Snakes.

Abstract

Morphometric measurements are basic but essential data in morphological and ecological research. It is thus beneficial to develop a safe, convenient, multipurpose device/technique to determine body length and physical characteristics of living snakes with high accuracy/precision and low stress, and to enable the probing of snakes and collection of tissue samples. To meet these requirements, we developed an improved technique, which we named the Confining-Box Method (CBM). On measuring the body lengths of a total of 72 live snakes, we found significant differences in the accuracy and precision of measurements among the squeeze-box method, the anesthesia method, and the CBM, as well as between vertebral line and the mid-ventral line measurements. Body lengths, as measured along the vertebral line and corrected for perspective errors, using the CBM, did not differ significantly from the standard lengths measured by hand using anesthesia. The squeeze-box method produced substantial negative bias and/or less precision in ventral measurements, especially for large snakes (> 1.2 m in snout-vent length). The differences between measurers were much smaller than among the different techniques. Compared to the anesthesia technique, CBM is a fast and simple method that is also safer for snakes. Unlike the traditional squeeze-box technique, CBM can record both dorsal and ventral body images of snakes simultaneously and enable researchers to measure accurate and/or precise total length (from dorsal images), tail length (from ventral images), and snout-vent length using images from a single photography session. CBM could therefore become a standard to improve measurement consistency, allowing improved data comparison in future studies.