In situ measurements of animal morphological features: A non-invasive method

Abstract

Measurements of morphological features are important for ecological studies, especially on free-ranging wild animal species. Conventionally, specimens either dead or in captivity are used for morphometric studies, which is difficult in the case of wild species for several reasons. Capturing would be even futile when research questions are relating to issues such as prey size selection or estimation of intake rate under field conditions, where in situ morphometric measurements are inevitable. Remotely estimating morphometric features via, avian bill and head lengths are always laden with wide variances. Hence, we developed this technique for in situ measurements of animal morphology through digital photographs. This non-invasive novel method for in situ estimation of individuals’ morphometric measurements uses digital photographs’ metadata. We extracted the metadata (field of view, focal length, subject-distance, etc.,) in exchangeable image file format from digital images using freely available software, and the unknown sizes were estimated from each image. Cardboard (fish) models were, at first, used to estimate the accuracy of measurements comparing actual and estimated values, and the same protocol was repeated on museum specimens (bird). Finally, we checked the repeatability of this method under field conditions using free-ranging Chickens (Gallus gallus domesticus). The results under different conditions were subjected to rigorous statistical testing. Upon comparing the actual with estimated values, obtained from three distinct types of objects (1. Cardboard model, 2. Museum specimens and 3. Live birds under field conditions), variations were found non-significant affirming the assumption that actual value (Y) = estimated value (X) with inconsequential variance of the Y from X. Moreover, both the relative and absolute errors between the actual and estimated values were so low, indicating that this method yielded neither overestimation nor underestimation. The advantage of this non-invasive method is that it could generate reasonably accurate morphometric measurements at a relatively low cost for routine morphometric works in field conditions. We envisage significant utility of this non-invasive technique in different fields of science such as biology, morphology, ecology, evolution, wildlife, conservation science, agriculture, forensics and engineering design.