The impacts of marking on bats: mark-recapture models for assessing injury rates and tag loss

The individual identification of animals is essential for long-term population ecology studies. Injuries and tag loss can negatively impact animal welfare and parameter estimates. We used time-to-failure curves and multistate mark-recapture models to estimate injury rates, body condition decline, tag loss and survival probabilities associated with two tags commonly used in bats: metallic arm bands and steel ball chain collars. We monitored two colonies of Carollia perspicillata at União Biological Reserve, southeastern Brazil, from 2013 to 2019. Every other month, we marked individuals with arm bands, collars or both. Collars did not cause noticeable injuries, but were lost at a higher rate than arm bands (1.5–2.5 times). The arm band-related injury probability between captures was ~ 0.2, and after 17 months half the marked animals developed injuries. Animals marked as juveniles were less likely to get injured than adults. Injuries were associated with a lower body condition in females. Body condition was positively associated with apparent survival; however, a direct effect of arm band injuries on survival estimates was not observed. The tag loss rates caused a negative bias in survival estimates. Mark-recapture studies should evaluate the efficacy of the marking technique, accounting for potential animal injury, tag loss, and bias in parameter estimation. Marking individuals should be limited to studies that monitor species with high recapture probability, using the least harmful tags possible, and balancing the burden to the animals with the potential to generate knowledge.