DOI: 10.5061/dryad.b2rbnzsjx
title: Do departure and flight route decisions correlate with immune parameters in migratory songbirds?

description: 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
 (immunoglobulin Y) in the birds’ plasma. After sampling, we tracked the
 birds’ behavior in terms of stopover duration as well as flight routes and
 flight distances within the telemetry network after departure. We found
 that stopover durations were positively related to natural antibodies and
 immunoglobulin Y across species and to the bacterial killing ability
 solely in song thrushes in spring, while no relations became apparent in
 fall. Flight distances were linked positively to immunoglobulin Y
 concentrations in both spring and fall, though not in all of the
 investigated species. Coastal and offshore-oriented routes were taken
 independent of the birds’ immune status. Our study for the first time
 shows that the migratory behavior of songbirds in the wild is correlated
 with their immune status, not only during but also beyond stopover.
 Further, birds with increased complement titers and Immunoglobulin Y
 concentrations, either due to recent infection or greater investment in
 their immune function, took additional time at their stopover sites,
 probably to reach their breeding grounds in good condition. During the
 less time-constrained fall season, stopovers were generally prolonged,
 independent from the birds’ immune status, and any delays taken to improve
 immune status are most likely not detrimental in terms of fitness.
description: Birds of five species of short- to medium-distance migrating
 songbirds were caught at the coast of Schleswig-Holstein, Germany during
 three consecutive autumn seasons, blood sampled and released with
 radio-telemetry tags. From blood samples, four parameters of the constitutive innate
 immune system (bacterial killing activity against <em>Escherichia
 coli</em>, lysozyme concentration, natural antibodies and complement
 titers and one component of the constitutive acquired immune system (total
 immunoglobulin Y concentration) were measured. From radio-telemetry data
 filtered for false positive detections (see Brust et al. 2019 for
 details), we assessed the duration of stopover at the coast, taken route,
 and flown distance within the radio-telemetry network.
description: Data are provided as R dataframe.