Adaptive protocols identify sources of post-capture mortality in radio-marked wild turkeys

Abstract

Context Stress or injury resulting from capture and marking of animals is a potential cause of mortality following release. Multiple methods have been developed to identify sources of post-capture mortality, but these are most often applied following completion of field work to identify an appropriate censor window for other analyses. Aims Following unacceptable levels of post-capture mortality (13 of 53) in radio-marked individuals in the first year of a larger wild turkey research project in Maine, USA, we assessed post-capture survival as data became available to inform proactive changes to capture protocols, with the goals of improving animal welfare and data quality. Methods We evaluated potential sources of post-capture mortality related to the capture and marking process, individual characteristics of the turkey, and local weather conditions. We then used results from the preliminary analysis to inform adaptive changes to capture protocols in subsequent years and confirmed the effectiveness of these changes through a final analysis. Key results We found that greater handling time was positively correlated with increased post-capture survival, possibly in response to releasing turkeys in larger groups to facilitate regrouping. We also found that transmitter style impacted post-capture survival, such that female turkeys fitted with backpack-style transmitters experienced a survival rate of 0.787 (0.677–0.861 95% CI), compared with 0.903 (0.538–0.976 95% CI) for those fitted with a necklace transmitter, although adjustments to the fit of backpack transmitters appeared to help mitigate such issues. Conclusions Following informed adjustments to our capture protocols, we observed a dramatic increase in post-capture survival such that no mortalities were experienced in the first 30 days post capture in the final year of our study (n = 65). Although our estimated censor window was similar to other studies (~10 days), differences in effects of external stressors further the need for adaptive capture protocols because local stressors and risks may vary according to climate and ecosystem characteristics such as predator communities and habitat type. Implications We recommend that when possible, investigators continuously assess their protocols throughout the capture process and adapt accordingly to limit negative repercussions of capture and handling to wildlife.