Birds as hosts

Emerging infectious diseases are on the rise, and can impact public health and ecosystems. Wild birds are key hosts for several emerging (zoonotic) pathogens. Birds may themselves be impacted by disease, as I show in this thesis: outbreaks of the mosquito-borne Usutu virus in the Netherlands coincided with marked reductions in the survival probabilities and considerable population decline in Common blackbirds. A better understanding of variation in the host competence of birds can help us explain and predict disease emergence and its consequences. The immune system structures the transmission dynamics of parasites, and modulates the fitness consequences of infection for the individual. By studying how wild birds trade-off immune investments against investments in competing demands, I explored sources of variability in host competence across avian annual cycles. Ultimately, these studies can contribute to accurate model predictions of (emerging) disease outbreaks and their consequences for avian host populations. Collaboration with other disciplines will be essential in working towards this goal.