Dynamics of stress-induced changes of leukocyte profile in Great Tits: testing effect of age

Leukocyte profile parameters are often used as indicators of individual condition, long-term stress and immune system state in birds and other animals. Therefore, it is important to obtain baseline values of leukocyte profile parameters unaffected by stressful stimuli, including capture and handling. However, information about the timing of stress-induced changes in the leukocyte profile has been obtained only for a limited number of species, and there is little data on how various factors (e.g. environmental stimuli, life-history stage or age) affect these changes. In our study, we examined the dynamics of changes in leukocyte profiles following capture in male Great Tits ( Parus major ), and tested the effect of age on these dynamics. The numbers of lymphocytes, heterophils and heterophil to lymphocyte ratio (HL ratio) began to change between 30 and 60 min after capture, while significant changes in the total white blood cell (WBC) counts appeared later, 60–90 min after capture. Eosinophil numbers were stable within 90 min of capture. We did not observe an effect of age on the timing of stress-induced changes in the leukocyte profile. Overall, our results corroborate previous data obtained from Great Tits but disagree with data for some other avian species. We assume that the dynamics of leukocyte profile changes are likely to be species-specific. We conclude that to obtain baseline values of leukocyte profile parameters, blood samples should be preferably taken within 30 min after capture.