Figure 3.

Annual and circannual cycle in an immune parameter. The capacity of whole blood to kill cultures of Staphylococcus aureus is shown for 3 experimental groups of songbirds, stonechats (genus Saxicola). Siberian (blue) and Kenyan (green) stonechats were kept in a common garden setup of annually changing European photoperiod (PP) over 1 year, where they showed distinct, population-specific annual cycles (Versteegh et al., 2014). Groups were measured per life cycle stage because the populations differed in duration of phases such as migration or molt (annual cycle stages 1-5: spring migration; breeding season; molt; autumn migration; winter). An additional Kenyan (red) group (Versteegh, Tieleman & Helm, unpubl.) that was kept under constant photoperiod showed similar, circannual cycles; curves indicate loess smoothing. Color version is available online.