Effects of altered diet and habitat use on stress and immune function of White Ibis (Eudocimus albus) in urban South Florida

White Ibises, a Florida species of special concern, are abundant in urban Palm Beach County, Florida (PBC) and present at urban parks where they are habituated to people and provided consistent supplemental food. Urban ibis... [ view full abstract ]

White Ibises, a Florida species of special concern, are abundant in urban Palm Beach County, Florida (PBC) and present at urban parks where they are habituated to people and provided consistent supplemental food. Urban ibis congregate at high densities; interact regularly with wildlife, domestic animals, and humans; consume nutritionally poor handouts including white bread; and are exposed to novel pathogens via other birds and environmental contamination. Overall, these ecological changes affect ibis stress and immunity. Ibis were captured at seven sites in PBC July–December 2013 and evaluated to determine the influence of diet (stable isotopes) and urban habitat use (telemetry tracking) on baseline stress (fecal corticosterone; plasma corticosterone at capture), stress response (peak plasma corticosterone post-capture), and innate immune function (plasma bactericidal capacity). Urban ibis show evidence of chronic stress based on high fecal corticosterone levels compared to published studies of wild ibis and other species. Ibis also demonstrate dampened plasma corticosterone stress response at 15 minutes post-capture, suggesting chronic stress. Such stress is immunosuppressive, and urban ibis exhibit reduced immune function compared to most avian species, measured by a bacterial killing assay in which ibis plasma exhibited low bacterial killing ability at the lowest blood dilution (1:4 for ibis, compared to 1:10 or 1:20). Preliminary models of stress and immune function suggest that time spent in urban habitats is more important than diet in explaining baseline fecal and plasma corticosterone, but not bactericidal capacity. Effective management of ibis in urban habitats—including possible regulation of supplemental feeding—depends on understanding how dietary shifts and increased urban habitat use affect ibis stress and immune function (which affect the likelihood of ibis infection with pathogens including Salmonella spp., which are of documented high prevalence in PBC ibis). Such management may be necessary to minimize pathogen transmission risk to ibis, wildlife, and the public.