Meeting Abstract

76.4  Wednesday, Jan. 6  Variation in constitutive immune function in a long distance migrant shorebird during migratory stopover in Delaware Bay BUEHLER, Deborah M*; TIELEMAN, B. Irene; PIERSMA, Theunis; Royal Ontario Museum; University of Groningen; University of Groningen d.buehler@utoronto.ca

Delaware Bay, USA, is used by thousands of shorebirds as a final stopover site before migration to breeding areas in spring. The bay provides them with abundant food, horseshoe crab (Limulus polyphemus) eggs, which they use to lay down fat stores necessary for continued migration and subsequent survival on the breeding grounds. However, abundant food attracts dense mixed-species flocks, which may facilitate pathogen transmission, while migration itself may suppress immune defense. Despite the potential importance of disease risk and immune function during migration, little is known about how immune function changes during stopover in migratory shorebirds. To examine this, we measured constitutive immune function in Red Knots (Calidris canutus rufa) during stopover in Delaware Bay. We found lower total leukocyte, lymphocyte and monocyte concentrations, complement-mediated lysis, and haptoglobin activity in birds recovering protein after migration than in birds laying down fat as fuel for subsequent flight. We discuss two possible reasons for this result. First, fueling birds may have an increased rate of infection or be bolstering immune defense in response to high antigen exposure. Second, recovering birds may be immunocompromised due to the physical strain of migratory flight or due to adaptive trade-offs between immune function and migration.