Using Scale Pattern Variation to Identify Individuals in the Long-Lived Reptile, Egernia rugosa

Effective population monitoring programmes rely on identifying individual animals accurately and ethically without negatively impacting their natural behaviour and survival. This study aimed to determine if the chin scale patterns of the threatened yakka skink (Egernia rugosa) could be used to consistently identify individual skinks. We examined the pattern uniqueness by monitoring (1) juveniles within the same aggregation, (2) juveniles across aggregations and (3) all ages caught across all years. Finally, we trialled the utility of the process by testing 14 experienced and 14 inexperienced people to see if they could correctly identify recaptured lizards from different age cohorts and aggregations, and the timeliness of undertaking manual identification. We identified 377 individual skinks over the length of the study using their unique chin patterns. Juvenile skinks both from the same and different aggregations had unique chin patterns allowing individuals to be correctly identified. A total of 190 skinks (50.4%) were recaptured. Chin pattern stability was confirmed by the recapture of 76 sub-adult skinks between 2021 and 2023 during a period where the skinks had undergone a substantial increase in body size. Pattern stability was also recorded in 43 mature skinks that were recaptured over an extended period of 1–15 years (mean 4.9 years). Experienced and inexperienced volunteers successfully identified known individuals 96.5% and 97.6% of the time, respectively, and importantly, the level of experience did not influence the time required by participants to make an accurate identification. Natural chin scale pattern variation was shown to be an effective and efficient means to identify individuals of this species. Natural pattern variation should be considered a reliable alternative to more invasive reptile marking procedures (e.g., toe clipping) and for use with other reptiles with natural and stable scale pattern variation.