Condition-dependent immune response in a migrating shorebird, the common snipe Gallinago gallinago

Bird migration, as an energy-demanding activity, is expected to generate allocation trade-offs between important biological processes, such as immune response. On one hand, long-distance migratory flights may require redirection of resources from immune response and promote temporal immunosuppression. On the other hand, individuals in high body conditions may have the capacity to cope with the costs of migration while maintaining adequate levels of immune activity. Here, we investigated the covariation of immune response and two measures of condition in a short-distance migratory shorebird, the common snipe Gallinago gallinago. We captured and experimentally induced immune response using phytohaemagglutinin (PHA) in 148 snipes during the autumn migration. We found a positive relationship between PHA-induced immune response with indices of body condition reflecting aerobic capacity (total blood haemoglobin concentration) and the level of accumulated energy reserves (size-corrected body mass). The results provided evidence for condition-dependent immune response in migrating snipes, indicating that high-quality individuals are capable of sustaining optimal, non-suppressed immune responses during migration. We suggest that abundant food resources at high-quality stopover sites may help individuals rapidly replenish body reserves essential for the effective functioning of the immune system. It also seems likely that the maintenance of adequate immune function or its upregulation may confer significant adaptive advantages under ecological conditions of increased pathogenic exposure during migration.