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

Abstract

These journeys are energetically demanding and 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 behaviour and departure decisions, studies on how birds' individual physiological condition and stopover decisions may be linked are scarce.2. 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 behaviour in five species of short-to mediumdistance migratory songbirds. We measured markers of the innate (bacterial killing activity, lysozyme concentration, natural antibodies and complement titres) and acquired immune function (immunoglobulin Y) in the birds' plasma.After sampling, we tracked the birds' behaviour in terms of stopover duration as well as flight routes and flight distances within the telemetry network after departure.3. We found that stopover durations were positively related to natural antibodies and immunoglobulin Y across species and to the bacterial killing activity 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 offshoreoriented routes were taken independent of the birds' immune status. 4. Our study for the first time shows that migratory behaviour of songbirds in the wild is correlated with their immune status, not only during but also beyond stopover. Furthermore, birds with increased complement titres 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

The oxidative balance and stopover departure decisions in a medium- and a long-distance migrant

“…A potential difference with mainland stopover sites, however, is that the duration of stopovers on Helgoland may be shorter than on the mainland. For example, in the current Helgoland study more than half of the song thrushes departed the night after capture in autumn, whereas at a nearby (German North Sea coastline) mainland stopover site, median autumn stopover duration of song thrushes was 13 days [ 5 ]. Perhaps, some migrants leave Helgoland, as part of a landscape movement within the stopover environment [ 48 ], and fly to the mainland (ca.…”

Determinants of spring migration departure dates in a New World sparrow: Weather variables reign supreme

“…For example, several thrush species show lower total leukocyte counts upon arrival at stopover sites in spring, reflecting such trade‐offs (Owen & Moore, 2008 ). Variation in immune investment may in turn affect departure decisions; recent work demonstrated that songbirds with higher titers of natural antibodies and immunoglobulin Y have longer spring stopovers (Brust et al., 2022 ).…”

Departure, routing and landing decisions of long-distance migratory songbirds in relation to weather

“…atmospheric conditions, along the route [21] and adjust their migratory behaviour according to intrinsic factors, e.g. energy stores [22][23][24] and immune function [25,26]. For example, weather conditions that induce high metabolic costs of migratory endurance flights, such as headwinds, could lead to lower survival [27].…”