Question the Mark: A Review and Assessment of Bat Marking Practices

Background: It is often necessary to mark bats through tagging or other means to obtain essential information on their demography, movements and behaviour. However, marks may have lethal or sublethal effects and hence may bias study results. Understanding the effects of marks on bats will allow researchers and managers to develop guidelines to minimise effects. Aims: Our aim was to review the effects and efficacy of marking techniques used on bats. Our objectives were to (1) describe marks currently used in bat research to identify motivations for marking, trends in commonly used types of marks and trends in the reporting of efficacy and injury rates in the recent literature, and (2) synthesise the body of literature on effects and efficacies of marking. Methods: We conducted a targeted literature review and a systematic literature review. In the targeted review, we examined all papers on bat marking published from 2013 to 2022 in three bat- or mammal-focused journals to identify trends in bat marking over the past decade. The systematic review was a general review of papers that reported on the effects and efficacy of bat marking from the early 1900s to the present. Results: Our targeted review found that researchers rarely report the effects of marks on bats and many papers fail to provide details of the marks and marking procedures. Our systematic review found that the effects of marks ranged from minor irritation and behavioural changes to potentially life-threatening injuries, such as changes in body condition; fewer deleterious effects have been reported from newer marking procedures such as passive integrated transponder (PIT) tags. Conclusions: Further research on marking effects is needed, as well as more thorough reporting in the literature of marks and their effects so that useful guidelines can be developed.