Mark my words: experts’ choice of marking methods used in capture-mark-recapture studies of small mammals

Abstract

Crucial to the success of studies based on capture-mark-recapture (CMR) designs is the retention (permanency) and recognition (readability) of marks to identify individuals. Several marking methods for small mammals (< 60 g) are available, but their efficacy and use is not well known. We implemented a targeted survey of experts to gather their experiences and opinions regarding marking small mammals. Respondents (n = 114) stated their beliefs, perceptions, and current and future use, of marking methods, as well as factors influencing their choices, based on Likert and rank order scale questions. We compared responses based on where researchers’ studies occurred, their level of experience, and their subfield of mammalogy. Most respondents (73%) had > 5 years experience marking small mammals, with 60% each marking > 1,000 individuals. Respondents believed that ear-tagging was most preferable in terms of efficiency, impact to affected animals (survival, pain), and personal ethics, whereas passive integrated transponder (PIT)-tagging was the most preferable with regard to retention and recognition, and toe-clipping with respect to cost. Most respondents plan to use ear-tagging (78%) or PIT-tagging (70%) in the future. PIT- and genetic-tagging are expected to increase, and toe-clipping to decline, in the future. The factors influencing which marking method respondents used were ranked—in order of decreasing preference—as impact, retention, recognition, cost, efficiency, and ethics. There were few differences in the mean response or consensus among respondents, regardless of their experience, location, or subfield. Most respondents (66%) agreed that additional studies on the performance and impact of various marking methods are needed to assess their costs and benefits for CMR-based studies. Ultimately, choice of marking method will depend on the species, research question, available resources, and local legislation and permitting. Our study, however, illustrates that collective insights by experienced mammalogists may aid individual researchers in deciding on study designs and protocols, particularly early career scientists.

Estimating the density of small mammals using the selfie trap is an effective camera trapping method

“…Live trapping is the standard method for estimating population density of small mammals, with aspects such as trap detection probability and survey lengths (Batzli 1992;Prevedello et al 2013;Gentile et al 2018;Fuentes-Montemayor et al 2020), and mark retention and recognition (Jung et al 2020), as important considerations. Estimating densities with camera traps is achievable when the focal species features markings that allow for individual identification (e.g., Karanth 1995) or when animals have been caught and marked (Jung et al 2020), so that mark-recapture models can be used to estimate densities. However, where individuals cannot be distinguished, then hit rate data (number of camera trap events) can be applied to random encounter models (REMs) to estimate densities (Rowcliffe et al 2008).…”

Performance of helicopter-based biopsy darting of polar bears (Ursus maritimus) on the spring sea ice

“…Traditional means to individually mark large mammals for CMR-based studies has included radio-collars, lip tattoos, and ear-tags-all of which require capturing and restraining individuals to apply marks. However, when marking entails physically capturing and handling individuals, there may be concern regarding the impact on affected animals (e.g., McMahon et al 2012;Jung et al 2019Jung et al , 2020Latham et al 2020). This is particularly true for species with high social, cultural, or economic value.…”

Automatic identification of bird females using egg phenotype

“…Identification of individuals is important in zoological research, particularly when investigating variation among or within individuals in a population. Traditionally, capture-mark-recapture techniques have been used to monitor individuals during their lifetime (Lindberg, 2012; Jung, Boonstra, & Krebs, 2020). This method has been improved by employing more sophisticated methods such as attaching GPS (global positioning system) and radio transmitters or RFID (radio frequency identification) tags (Krause et al, 2013) that allow researchers to investigate the spatial activity of animals in more detail.…”