Vetmeduni: Water makes frog image recognition 100% clear
An Austrian-Hungarian study led by the Konrad Lorenz Institute of Ethology (KLIVV) at the University of Veterinary Medicine Vienna developed a new, optimized photography method. As the research on frogs shows, this raises the recognition of individuals to a new level. The trick behind it is simple: the animals are dipped in clear water and held by hand.
Identifying individuals across time and space is important for investigating numerous questions in evolutionary ecology and conservation. However, the success of available photo-matching software can strongly depend on image quality as well as the body parts in focus.
“We therefore tested whether identification of individuals based on color patterns could be improved by taking into account the animals’ natural environment and their natural body posture,” explains lead author Edina Nemesházi of KLIVV at Vetmeduni, outlining the reasoning behind her research. To test this idea, the researchers optimized existing photography procedures to individually identify agile frogs (Rana dalmatina) using full-body assessment. They then evaluated the reliability of this approach for both computer-assisted identification in the HotSpotter software and for observers working with it.
Previous photography methods deliver good, but not error-free, results
The researchers found that photographing frogs either held by hand with towel-dried skin (which is a conventional method) or moving freely in clean water allows comparison of the entire back of the body, including the hind legs. HotSpotter identified matching images at similarly high rates as in earlier frog studies. With these two methods, the actual match rate was still more than 92%.
Anything but superfluous: New underwater method identifies individuals with 100% accuracy
“However, dipping hand-held frogs into water significantly improved unambiguous identification: images of the same individual were always flagged as the most likely match, i.e., classified 100% correctly,” says Nemesházi.
According to the researcher, this outstanding performance is due to the combination of the advantageous effects of light refraction in water and standardized body postures. The former improves the visibility of pigment patterns, while the latter facilitates comparisons between individuals. According to Nemesházi, the photography method described in the study—i.e., taking the natural environment, water, into account—should be easily adaptable for reliable identification of individual frogs and toads in most species. Photographing frogs moving freely in water also proved to be a useful option for identification.
Contact:
Dr. Edina Nemeshazi, PhD.
Konrad-Lorenz-Institut für Vergleichende Verhaltensforschung (KLIVV)
Veterinärmedizinische Universität Wien (Vetmeduni)
Edina.Nemeshazi@vetmeduni.ac.at