Mean ±SD for immunological parameters in the five locations of the study.

Short-distance migrants: (Sisargas (Galicia, Spain); Delta (Ebro delta, Spain); Moerdjik (The Netherlands); Long-distance migrants: Häme (Finland); Kokkola (Finland). Units: natural antibodies (-log2 agglutination score), complement (-log2 lysis score), IgY, Haptoglobin and Lysozyme (Optical density). Higher OD values indicate lower lysozyme. abc denote differences among populations in post-hoc statistical analyses. Mean ±SD for immunological parameters in the five locations of the study.