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Photographic identification of individuals of a free-ranging, small terrestrial vertebrate
This is an open access article under the terms of the Creative Commons Attribution License, which permits use,
distribution and reproduction in any medium, provided the original work is properly cited.Recognition of individuals within an animal population is central to a range of
estimates about population structure and dynamics. However, traditional methods
of distinguishing individuals, by some form of physical marking, often rely
on capture and handling which may affect aspects of normal behavior. Photographic
identification has been used as a less-invasive alternative, but limitations
in both manual and computer-automated recognition of individuals are
particularly problematic for smaller taxa (<500 g). In this study, we explored
the use of photographic identification for individuals of a free-ranging, small
terrestrial reptile using (a) independent observers, and (b) automated matching
with the Interactive Individual Identification System (I3S Pattern) computer
algorithm. We tested the technique on individuals of an Australian skink in the
Egernia group, Slater’s skink Liopholis slateri, whose natural history and varied
scale markings make it a potentially suitable candidate for photo-identification.
From ‘photographic captures’ of skink head profiles, we designed a multichoice
key based on alternate character states and tested the abilities of observers
— with or without experience in wildlife survey — to identify individuals
using categorized test photos. We also used the I3S Pattern algorithm to match
the same set of test photos against a database of 30 individuals. Experienced
observers identified a significantly higher proportion of photos correctly (74%)
than those with no experience (63%) while the I3S software correctly matched
67% as the first ranked match and 83% of images in the top five ranks. This
study is one of the first to investigate photo identification with a free-ranging
small vertebrate. The method demonstrated here has the potential to be applied
to the developing field of camera-traps for wildlife survey and thus a wide
range of survey and monitoring applications