DOI: 10.5061/dryad.kkwh70s4n
title: Linking camera-trap data to taxonomy: Identifying photographs of morphologically similar chipmunks

description: Remote cameras are a common method for surveying wildlife and recently
 have been promoted for implementing large-scale regional biodiversity
 monitoring programs. The use of camera-trap data depends on the correct
 identification of animals captured in the photographs, yet
 misidentification rates can be high, especially when morphologically
 similar species co-occur, and this can lead to faulty inferences and
 hinder conservation efforts. Correct identification is dependent on
 diagnosable taxonomic characters, photograph quality, and the experience
 and training of the observer. However, keys rooted in taxonomy are rarely
 used for the identification of camera-trap images and error rates are
 rarely assessed, even when morphologically similar species are present in
 the study area. We tested a method for ensuring high identification
 accuracy using two sympatric and morphologically similar chipmunk
 (Neotamias) species as a case study. We hypothesized that the
 identification accuracy would improve with use of the identification key,
 and with observer training, resulting in higher levels of observer
 confidence and higher levels of agreement among observers. We developed an
 identification key and tested identification accuracy based on photographs
 of verified museum specimens. Our results supported predictions for each
 of these hypotheses.  In addition, we validated the method in the
 field by comparing remote camera data with live-trapping data. 
 We recommend use of these methods to evaluate error rates and to exclude
 ambiguous records in camera-trap datasets. We urge that ensuring correct
 and scientifically defensible species identifications is incumbent on
 researchers and should be incorporated into the camera-trap workflow.
description: We tested the efficacy of our final identification key by
 comparing the accuracy of observers using identification resources from
 the literature (hereafter, “literature observers”; N=19) to that of
 observers using our identification key (hereafter, “key observers”; N=15).
 We provided all observers with Adobe PDF files that included instructions,
 identification resources, and a test. We provided the literature observers
 with identification resources that consisted of excerpts from
 <i>Mammalian Species</i> accounts for both species (Best et
 al., 1992; Verts and Carraway, 2001) and a popular field guide to North
 American mammals (Reid, 2006). These materials represented the best
 available identification information attainable without examining
 specimens. We highlighted sections pertaining to pelage traits to guide
 observers to the most relevant information for identifications from
 photographs. We provided the key observers with the identification key.
 For both groups of observers, the test consisted of 20 slides, each
 showing three views of a single chipmunk specimen (dorsal, lateral, and
 ventral). We used three views for testing because in our field
 applications cameras fire multiple times providing photographs of an
 animal from multiple angles – on average, we captured 10.6 photographs of
 a chipmunk with each visit to a camera and only 7.2% of chipmunk visits to
 a camera resulted in a single photograph. For each slide, observers
 recorded a species identification and the numeric confidence-rank. Numeric
 confidence-ranks ranged from 1 to 4 for each slide, based on the
 observer's confidence in the attribution of species, from 1: no
 confidence, 2: not very confident, 3: somewhat confident, 4: very
 confident. Observers could only view their own responses during the
 testing process. The observers were field technicians working on chipmunk
 field research or undergraduate students in wildlife biology, but they did
 not have any prior knowledge about chipmunk identification.
 We tested if a training
 program would improve the accuracy of observers who used our
 identification key. All key observers (N=15) completed the training
 program. For the training program, observers practiced using the
 identification key to identify photographs of chipmunk specimens in two
 separate training sets. After each training set, we provided the trainees
 with the answer key, so that they could compare their answers to the
 correct answers and learn from mistakes. The first training set was the
 original 504 randomized slides showing nonants of specimens of chipmunks,
 used by the authors for the development of the identification key. The
 trainees coded each slide for each pelage trait, assigned a species
 identification based on their overall impression, and reported a numeric
 confidence-rank, following the procedure used for the development of the
 key. The second training set consisted of 168 randomized slides showing a
 single view (dorsal, lateral, or ventral) of a specimen. For each slide,
 the trainee assigned a species identification and reported a numeric
 confidence-rank. After completing both training sets and reviewing the
 correct identifications, we considered observers to be fully trained
 (hereafter “trained key observers”). We tested trained key observers using
 a post-training test, which consisted of a set of 56 slides, each showing
 three views of a single chipmunk specimen (dorsal, lateral, and ventral).
 For each slide, observers recorded a species identification and the
 numeric confidence-rank.