Time-keeping programme can explain seasonal dynamics of leukocyte profile in a migrant bird

It has been proposed that immune functioning in wild animals is shaped by the trade-off between a probability of encountering pathogens and an availability of resources for maintaining immune system in active state. Due to resources’ seasonality one can expect that immune functioning, e.g., absolute and relative counts of white blood cells, WBC (leukocyte profile) also follows an annual cycle. However, dynamics of the seasonal changes of leukocyte profile are controversial and specific inquiries so far addressed only a portion of annual cycle. To study the seasonal dynamics of the leukocyte profile and to test its possible endogenous basis we experimentally simulated annual cycle in a migratory passerine bird, chiffchaff (Phylloscopus collybita abietinus). We report here a clear seasonal pattern of leukocyte profile in that species. The highest WBC counts were observed during pre-alternate moult and the lowest during the subsequent spring migration; the seasonal dynamics of HL ratio sh...