Abstract
Reliable identification of individuals plays an important role in behavioural studies of free-ranging animal populations. In field studies of elephants, the naturally acquired markings on their ears, such as notches, tears and holes, are frequently used for individual identification. Although not as easily discernible from a distance as ear markings, the facial wrinkle pattern around the eye, temporal gland and ear on both sides of elephant’s head are individually unique and, with application of high-resolution photographs, can also be used for individual identification. In fact, the wrinkle pattern is highly consistent and reliable as the primary identifiable feature; it changes little over time, facilitates identification of individuals with non-distinctive ear pattern (e.g., calves), and performs well against several practical challenges to the traditional ear-pattern approach. We used data from a 3-year photo-identification study of African elephant population to examine how the two identification methods, one that uses marks on elephant ears and the other using facial wrinkle pattern, affect the results of basic analyses of social dynamics, such as patterns of associations and social preferences, derived from datasets generated with these two identification methods. Comparative analyses demonstrate that by increasing the identifiability of otherwise poorly marked individuals and minimising identification error, the wrinkle-based method reduces substantially the sample bias, enhances the robustness of datasets, and minimises analytical error. While ear-pattern-based distinctiveness is age-dependent, the wrinkle-based method facilitates a more representative sample of the population, with photo-ID data collected non-discriminately across all age classes. This carries further implications, such as enabling more accurate depiction of elephant sociality, long-term population monitoring, calculation of class-specific population parameters, etc. Adopting the facial wrinkle pattern for elephant individual identification is relatively easy, and we encourage future and ongoing studies to consider incorporating the facial wrinkle approach. Given the advantages of wrinkle-based identification and recent advances in machine learning, we recommend it to be considered for the development of automated matching algorithms; such development would benefit long-term socio-behavioural studies and monitoring of elephant populations.
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Acknowledgements
We thank the Pilanesberg National Park, Pilanesberg Wildlife Trust and North West Parks Board for their logistic support, and Dr. Yolanda Pretorius for facilitating this project. Our special gratitude goes to Charlotte Marais, Steve Dell and Perry Dell for greatly facilitating our fieldwork and their indispensable help throughout the project. Accommodation, logistics, and partial fieldwork expenses were supported by Copenhagen Zoo, Denmark, which is gratefully acknowledged. We thank the two editors and two external reviewers for their valuable comments.
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Fieldwork expenses and logistics were supported by Copenhagen Zoo, Denmark.
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LK and SYSC contributed equally to conceptualising and designing the methodology; SYSC collected and analysed the data; SYSC prepared the initial draft of the manuscript; both authors contributed equally to revising and preparing the final manuscript.
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Handling editors: Daniel I. Rubenstein and Stephen C.Y. Chan.
In memory of Kobus Marais, Counter Poaching Unit, Pilanesberg National Park.
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This article is a contribution to the special issue on “Individual Identification and Photographic Techniques in Mammalian Ecological and Behavioural Research – Part 1: Methods and Concepts” — Editors: Leszek Karczmarski, Stephen C.Y. Chan, Daniel I. Rubenstein, Scott Y.S. Chui and Elissa Z. Cameron.
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Appendix
The facial wrinkle pattern on the left side of an adult male elephant (LB032). The photographs were taken a year apart. The pattern of wrinkles around the eye, temporal gland and ear (indicated with green lines) represents a reliable feature for elephant individual identification
The facial wrinkle pattern on the right side of an immature male elephant (GY015). The photographs were taken ten months apart. As this individual does not have distinctive markings on its right and left ear, its identity could not be verified with traditional ear-pattern-based identification methods. The facial wrinkles (indicated with green lines) on the other hand, provide a reliable feature for the identification of less- or “non-distinctive” individuals
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Chui, S.Y.S., Karczmarski, L. Everyone matters: identification with facial wrinkles allows more accurate inference of elephant social dynamics. Mamm Biol 102, 645–666 (2022). https://doi.org/10.1007/s42991-022-00257-z
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DOI: https://doi.org/10.1007/s42991-022-00257-z