Data from: Migration distance does not predict blood parasitism in a migratory songbird

Migration can influence host-parasite dynamics in animals by increasing
exposure to parasites, by reducing the energy available for immune
defence, or by culling of infected individuals. These mechanisms have been
demonstrated in several comparative analyses; however, few studies have
investigated whether conspecific variation in migration distance may also
be related to disease susceptibility. Here, we ask whether autumn
migration distance, inferred from stable hydrogen isotope analysis of
summer-grown feathers (δ2Hf) in Europe, correlates with blood parasite
prevalence and intensity of infection for willow warblers (Phylloscopus
trochilus) wintering in Zambia. We also investigated whether infection was
correlated with individual condition (assessed via corticosterone, scaled
mass index, and feather quality). We found that 43% of birds were infected
with Haemoproteus palloris (lineage WW1). Using generalized linear models,
we found no relationship between migration distance and either
Haemoproteus infection prevalence or intensity. There was spatial
variation in breeding ground origins of infected vs. non-infected birds,
with infected birds originating from more northern sites than non-infected
birds, but this difference translated into only slightly longer estimated
migration distances (~214 km) for infected birds. We found no relationship
between body condition indices and Haemoproteus infection prevalence or
intensity. Our results do not support any of the proposed mechanisms for
migration effects on host-parasite dynamics, and cautiously suggest that
other factors may be more important for determining individual
susceptibility to disease in migratory bird species.