This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Identifying individual animals in the wild has long meant tagging, branding or clipping. For amphibians, the standard approach has often been toe-clipping, a procedure that can affect survival, physiology and behavior.
A new study suggests that, for at least one species of treefrog, nature has already provided a more humane solution: the eyes. Published in the open-access journal Herpetozoa, the research was led by Dr. Mélissa Peignier and colleagues at the Division of Behavioural Ecology at the University of Bern, with contributors from the Institute of Electronic Music and Acoustics at the University of Music and Performing Arts in Graz.
The team examined Osteocephalus oophagus, an Amazonian treefrog whose golden irises are crossed by fine black radial lines, forming a pattern reminiscent of a human fingerprint. Fieldwork took place over three rainy seasons, from 2021 to 2023, on a river island of roughly 5 hectares (12 acres) in the Nouragues Nature Reserve in French Guiana. Across 392 captures, the researchers identified 103 individual frogs.
On later encounters, they photographed each animal's eyes without touching it and compared the images with a reference library held on a rugged tablet. Frogs recognized in this way were simply left undisturbed. The identifications were independently verified using Wild-ID, a software package for photographic mark-recapture analysis.
The iris patterns proved highly distinctive. Within a single season, between 56% and 80% of frogs were recaptured and reliably reidentified, showing that the patterns are stable enough for short-term monitoring. Photographs could even be taken of frogs in amplexus, the mating embrace, without disrupting them.
The project began with simple admiration. "At the time, I was doing my Ph.D., studying Allobates femoralis in the field in French Guiana," says Peignier. "My first reaction was simply something along the lines of, 'Wow, what beautiful eyes!' That initial curiosity gradually turned into a genuine interest in the species, and I realized how little we actually know about them." The team's motivation was also ethical.
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