Meeting Abstract
Migratory birds move through multiple habitats and encounter a diverse suite of parasites. This raises concern over migrants’ potential role in transporting infectious disease between the breeding and wintering grounds, and along migratory flyways. Trade-offs between migratory flight and immunity may result in parasitized individuals delaying migration, with important effects on infection dynamics. However, experimental evidence that parasitic infection affects migratory timing remains scant. We hypothesized that encountering haematozoan parasites alters migratory timing and body condition, due to the infection itself and/or to the costs of mounting an immune response. To test this hypothesis, we experimentally inoculated song sparrows (Melospiza melodia) with an endemic strain of Plasmodium shortly before fall migration. We monitored infection success and body composition, and used radiotelemetry and mark-recapture analysis to infer migratory departure after release. Individuals that resisted acute infection despite exposure to parasites had lower lean mass twelve days after exposure than individuals that became acutely infected or controls inoculated with uninfected blood. This suggests trade-offs between body composition and immunity, either because resistance is energetically costly and/or because heavier individuals are more susceptible to infection. By contrast, we observed no significant difference between the resistant, acutely-infected, and control groups in timing of migratory departure. Experimentally evaluating the effects of infection and resistance on migratory timing and preparation in free-living animals is increasingly crucial, as parasite and vector ranges shift in response to a changing climate.
