Optimising the automated recognition of individual animals to support
population monitoring
Abstract
Reliable estimates of population size and demographic rates are central
to assessing the status of threatened species. However, obtaining
individual-based demographic rates requires long-term data, which is
often costly and difficult to collect. Photographic data offer an
inexpensive, non-invasive method for individual-based monitoring of
species with unique markings, and could therefore increase available
demographic data for many species. However, selecting suitable images
and identifying individuals from photographic catalogues is
prohibitively time-consuming. Automated identification software can
significantly speed up this process. Nevertheless, automated methods for
selecting suitable images are lacking, as are studies comparing the
performance of the most prominent identification software packages. In
this study, we develop a framework that automatically selects images
suitable for individual identification, and compare the performance of
three commonly used identification software packages; Hotspotter,
I3S-Pattern, and WildID. As a case study, we consider the African wild
dog Lycaon pictus, a species whose conservation is limited by a lack of
cost-effective large-scale monitoring. To evaluate intra-specific
variation in the performance of software packages, we compare
identification accuracy between two populations (in Kenya and Zimbabwe)
that have markedly different coat colouration patterns. The process of
selecting suitable images was automated using Convolutional Neural Nets
that crop individuals from images, filter out unsuitable images,
separate left and right flanks, and remove image backgrounds. Hotspotter
had the highest image-matching accuracy for both populations. However,
the accuracy was significantly lower for the Kenyan population (62%),
compared to the Zimbabwean population (88%). Our automated image
pre-processing has immediate application for expanding monitoring based
on image-matching. However, the difference in accuracy between
populations highlights that population-specific detection rates are
likely and may influence certainty in derived statistics. For species
such as the African wild dog, where monitoring is both challenging and
expensive, automated individual recognition could greatly expand and
expedite conservation efforts.