Do departure and flight route decisions correlate with immune parameters in migratory songbirds?

Many songbirds migrate twice a year to exploit seasonally available resources. These journeys are energetically demanding and the energy reserves of these small birds are limited. Accordingly, most of the time migrating is spent during stopovers that serve to rest, replenish resources and recover. While external influences, like prevailing weather conditions and resource availability, are well studied with regard to stopover behavior and departure decisions, studies on how birds’ individual physiological conditions and stopover decisions may be linked are scarce.
We used a large-scale radio-telemetry network covering the German Bight (SE North Sea) to study how birds’ immunological constitution at stopover may correlate with departure and flight behavior in five species of short- to medium-distance migratory songbirds. We measured markers of the innate (bacterial killing activity, lysozyme concentration, natural antibodies, and complement titers) and acquired immune function (immunoglob...