Turkey Vulture survival is reduced in areas of greater road density

The demography of, and factors that influence these metrics, are largely unknown for most vultures in the Americas. Survivorship of Turkey Vultures (Cathartes aura) may be influenced by landscape heterogeneity and human disturbance. We quantified the effects of landscape composition (Shannon's diversity index) and configuration (contagion, edge density, and largest patch index), and human disturbance (road density) on the annual and seasonal survival probabilities of the three North American breeding populations (western, central, and eastern) of Turkey Vultures that spend the nonbreeding season in the southeastern portion of the Nearctic and the northern Neotropics during a 17-year period. We used Cox's proportional hazards models with time-varying covariates to estimate spatial and temporal changes in survival rates of adult Turkey Vultures. Road density, but not landscape composition or configuration, influenced survival rates in space and time. Overall annual survival averaged 0.87 (95% confidence interval [CI]: 0.74-0.98). Mortality risk was low in western and central populations (hazard ratio < 1) but was 3.7 times greater for vultures in the eastern population. Survival during the breeding (0.97, 95% CI: 0.96-0.98) and outbound migration (1.0, 95% CI: 1-1) seasons was significantly higher than the other seasons. Average survival tended to be higher for nonbreeding (0.81, 95% CI: 0.71-0.88) compared to return migration (0.69, 95% CI: 0.56-0.81) seasons. The risk of mortality for all vulture populations increased with road density, and this was greater during the nonbreeding and return migration seasons. The spatial variation in road density across the Americas may generate a network of ecological traps for Turkey Vultures induced to stop in areas of greater road-kill abundance. Road-killed animals acting as an attractant for vultures can increase the occurrence of vulture-vehicle collisions and potentially aggravate human-wildlife conflicts. Further analyses are needed to address survivorship and mortality factors for young birds. Our results may help the implementation of specific mitigation efforts to reduce human-vulture conflicts and vulture mortality. For instance, concentrating efforts to remove road-killed animals in areas where road density is highest can likely reduce vulture-vehicle collisions and associated mortalities of these birds. Lay Summary & BULL; Prior to this study, the factors affecting the survival of Turkey Vultures in the Americas were practically unknown. We combined Turkey Vulture movement data with updated geographic information layers to model annual and seasonal survival as a function of environmental covariates within a 17-year period. & BULL; Overall average survival was high (>75%), but mortality risk increased with road density. Mortality risk was greater during the nonbreeding and return migration seasons. & BULL; The road networks across the Americas appears to create ecological traps for Turkey Vultures where road densities are high and can increase the occurrence of vulture-vehicle collisions and potentially aggravate human-wildlife conflicts. & BULL; Additional research may be warranted regarding the impact of other linear infrastructures, such as railways and powerlines, and the management of human-vulture conflict on long-term survival of Turkey Vultures. & BULL; In regions characterized by greater road density increased efforts of road-kill removal may reduce vulture-vehicle collisions and overall vulture mortality.