Can post-capture photographic identification as a wildlife marking technique be undermined by observer error? A case study using King Cobras in northeast Thailand.

Max Dolton Jones,Jack Taylor Christie,Colin Thomas Strine,Taksin Artchawakom,Surachit Waengsothorn,Samantha Nicole Smith,Pongthep Suwanwaree,Benjamin Michael Marshall,Bi-Song Yue

doi:10.1371/journal.pone.0242826

Max Dolton Jones, Jack Taylor Christie + Show 7 more

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https://doi.org/10.1371/journal.pone.0242826

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Abstract

Identifying individuals with natural markings is increasing in popularity to non-invasively support population studies. However, applying natural variation among individuals requires careful evaluation among target species, snakes for example have little validation of such methods. Here we introduce a mark-free identification method for King Cobras (Ophiophagus hannah) from the Sakaerat Biosphere Reserve, in northeast Thailand using both subcaudal scale pholidosis (scale arrangement and number) and unique ventral body markings to distinguish individuals. This project aims to evaluate the impact of observer error on individual identification. Observers of varying expertise, will distinguish between King Cobra individuals using identifying photographs from a previous study. We will ask randomly assigned observers to distinguish individuals via: 1) subcaudal pholidosis, 2) ventral body markings, and 3) combination of both measures. Using Bayesian logistic regression, we will assess the probability observers correctly distinguish individuals. Based on exploratory observations, we hypothesise that there will be a high probability of correct identifications using subcaudal pholidosis and ventral body markings. We aim to stimulate other studies implementing identification techniques for scrutinous assessment of such methods, in order to avoid subsequent errors during long-term population studies.

Highlights

Identifying individuals within populations is a fundamental assumption for a number of quantitative population analyses
We aim to evaluate if observer error is too high that it may undermine our method in being applied to future King Cobra population studies, or potentially extrapolated to other snake species with similar morphological and phenotypical traits
We identified King Cobras captured between 2013 and 2018, using systematic branding following the protocols of Winne et al [15], and subsequently switched to using passive integrated transponder (PIT)-tags; ensuring correct individual identification facilitating our identification method

Summary

Introduction

Identifying individuals within populations is a fundamental assumption for a number of quantitative population analyses. With confident identification we can estimate abundance [1], density [2], behaviour [3], growth rates [4] and survivorship [5, 6]; generating the required information for both management and conservation actions. Individual marking methods vary and depend upon the focal study species of a study. Noninvasive marking techniques include: neck collars [7], bands/rings [8,9,10] and external colour marks [11, 12]. Invasive techniques include tags [13], branding [14, 15], transponders [16, 17].

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