Wintering mallard survival is unaffected by brief anthropogenic disturbance on protected areas

Abstract

Human activities in natural areas can impose both lethal and non-lethal impacts on animals. Furthermore, anthropogenic disturbance is analogous to predation risk and can cause animals to adjust their behaviors to avoid humans. Quantifying whether disturbance-induced behavioral shifts affect individual fitness or population dynamics is needed to guide science-based conservation and management decisions. We experimentally disturbed GPS-marked mallards (Anas platyrhynchos) on sanctuaries weekly to evaluate the effects of brief pulses (1 h) of non-lethal anthropogenic disturbance on individual survival. We used Cox proportional hazard models to examine how single and cumulative disturbance affected survival and tested whether body mass or hunting season mediated the effects of disturbance. One hundred and eighty-eight mallards were disturbed ≥1 time resulting in 629 disturbance encounters. Only 3 individuals died immediately following disturbance, representing <0.5% of encounters. Collectively, we found no effect of disturbance on daily survival, and our cumulative disturbance model showed undisturbed mallards had lower survival than disturbed mallards. Standardized body mass or hunting season did not mediate the effect of disturbance on survival. Together, we concluded there was no effect of our brief experimental disturbance treatments on mallard survival. Instead, diurnal sanctuary use and individual characteristics, including age, sex, and standardized body mass, affected survival. Diurnal sanctuary use was positively related to survival, and for every 20% increase in diurnal sanctuary use, the risk of mortality decreased by 15%. Additionally, female mallards were 2.7 times more likely to die compared to males, and juveniles had a 53% greater risk of mortality than adults. Lastly, for every 100 g heavier than average mallards were, we found a 23% lower risk of mortality during our study. If a primary goal of waterfowl sanctuary is including non-consumptive recreational use, our results suggest controlled access (e.g., ~1 h/week) may have minimal effects on survival and be consistent with multi-use objectives on public lands with waterfowl sanctuaries. If additional recreational access to support multiple public uses is a goal on public lands managed as sanctuaries, we recommend future work identify disturbance thresholds at which point survival or other fitness metrics are impacted by disturbance related to public uses of protected areas.