Abstract
Capture‐mark‐recapture procedures are a basic tool in population studies and require that individual animals are correctly identified throughout their lifetime. A method that has become more and more popular uses photographic records of natural markings, such as pigmentation pattern and scalation configuration. As with any other marking tool, the validity of the photographic identification technique should be evaluated thoroughly. Here, we report on a large‐scale double‐marking study in which European adders (Vipera berus) were identified by both microsatellite genetic markers and by the pattern of head scalation. Samples that were successfully genotyped for all nine loci yielded 624 unique genotypes, which matched on a one‐to‐one basis with the individual assignments based on the head scalation pattern. Thus, adders considered as different individuals by their genotypes were also identified as different individuals by their head scalation pattern, and vice versa. Overall, variation in the numbers, shape, and arrangement of the head scales enabled us to distinguish among 3200+ photographed individual snakes. Adders that were repeatedly sequenced genetically over intervals of 2–3 years showed no indication whatsoever for a change in the head scale pattern. Photographic records of 900+ adders that were recaptured over periods of up to 12 years showed a very detailed and precise match of the head scale characteristics. These natural marks are thus robust over time and do not change during an individual's lifetime. With very low frequency (0.3%), we detected small changes in scalation that were readily discernible and could be attributed to physical injury or infection. Our study provides a conclusive validation for the use of photo‐identification by head scale patterns in the European adder.
Highlights
Studies of the ecology of populations provide basic information for understanding the dynamics of population numbers and are fundamental in applied fields such a conservation biology, wildlife management, and pest control
Our study provides a conclusive validation for the use of photo-identification by head scale patterns in the European adder
Double-marking studies provide a reliable way to compare the performance of two independent individual recognition procedures, but have rarely been applied to studies of natural markings (but see (Stevick, Palsbøll, Smith, Bravington, & Hammond, 2001; Gosselin, Sainte-Marie, & Sévigny, 2007; Drechsler, Helling, & Steinfartz, 2015))
Summary
Studies of the ecology of populations provide basic information for understanding the dynamics of population numbers and are fundamental in applied fields such a conservation biology, wildlife management, and pest control. Over the past 2–3 decades, natural markings have been increasingly used as an identification tool (Speed, Meekan, & Bradshaw, 2007) This procedure uses photographic images of distinctive natural features, such as color pattern to identify individual animals at capture and recapture occasions. Individual snakes can be identified by their head scalation pattern (photograph by Rudi Segers) numerous fieldworkers have frequently demonstrated stability in head scale patterns on the basis of recaptures of individual adders and other vipers over periods as long as 10+ years (Benson, 1999; Üveges, Halpern, Péchy, Posta, & Komlósi, 2012) Such observations do not deny the possibility that scale pattern changes do occur but go unnoticed, so that a single individual is erroneously identified as another individual upon consecutive captures. Our objectives are threefold: (1) to compare individual assignments obtained by the examination of head scalation patterns and by genotyping; (2) to assess and illustrate the extent of variation in head scale configurations and explore its potential to identify large numbers of snakes; and (3) to examine stability of the scalation pattern during the snakes’ lifetime and expose the rare occasions of observed scale changes
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