Seabird diet and transmission routes mediate the increase in pathogen prevalence with human disturbance

1Human disturbances can alter patterns of wildlife infection, but their effects are likely to differ between terrestrial and marine environments. Seabirds range across land and sea and are therefore exposed to diverse human pressures such as urbanization, agriculture, and landfills, as well as fisheries, shipping, and marine pollution. However, most literature on wildlife infection has focused on terrestrial hosts or single type of disturbance (e.g., urbanization). Studying seabirds, which exploit diverse diets and habitats, offers a unique opportunity to disentangle how disturbances at sea and on land, as well as diets, and transmission routes, can change pathogen prevalence at a global scale. We conducted a global literature review and extracted datasets on seabird infection status for a range of pathogens, seabirds diets (piscivore, invertivore, generalist), and pathogen transmission routes (contact-based, vector-borne, intermediate host) to link pathogen prevalence to human disturbances at sea and on land. Our results showed that the association between human disturbances and pathogen prevalence was mediated by species diets and differed across transmission routes. Across gradients of human disturbance at sea, pathogen prevalence in piscivorous seabirds increased from near zero to over 0.7, particularly for contact-based pathogens. Land-based disturbance was also associated with higher pathogen prevalence in generalists across transmission routes, whereas invertivores showed a negative association with terrestrial disturbance. These results indicate that piscivores are most vulnerable in heavily disturbed marine environments, while generalists face greater risk on highly disturbed lands, suggesting that effective disease mitigation will require targeted management actions in both environments.