Infectious diseases in natural songbird populations along a gradient of urbanization

Abstract

Natural environments are increasingly encroached upon by urban development. In the United States, over 80% of the human population now lives in metropolitan habitats. This demographic shift is accompanied by drastic and often permanent changes to the habitat within and around cities, with consequences for wildlife populations. Research has shown that urbanization dramatically alters the composition of wildlife communities, leading to overall loss of species richness and an increased abundance of urban-adapted species. Although urbanization probably lowers the abundance of many wildlife parasites, for some, transmission could increase due to changes in host community composition, greater vector abundance, or increased host susceptibility and recruitment rates. In this doctoral thesis, I investigated associations between wild songbird communities and their pathogens at sites representing an urban gradient in north-central Georgia (U.S.A.) to identify patterns of infection and to investigate potential mechanisms underlying these patterns. Major findings include: (1) antibody prevalence of West Nile Virus (WNV) in songbirds increased with greater measures of urban land use, (2) WNV antibody prevalence is negatively associated with avian community diversity and positively associated with avian abundance and a composite measure of community competence, (3) avian malaria infections were common in Northern Cardinals (Cardinalis cardinalis), though prevalence was higher in juveniles, and (4) Salmonella enterica serovar Muenchen strains were detected in songbirds sampled at one non-urban site, and these were genetically similar to strains previously identified in human outbreaks. In general, results of this dissertation have implications for predicting how wildlife pathogens will respond to future increases in urbanization. Further studies to investigate the mechanisms by which multi-host pathogens respond to urbanization, including reductions in host species diversity and changes in host condition and susceptibility, could aid in future conservation efforts and may facilitate the development of effective preventative measures against human disease.