White blood cell counts in house sparrows (Passer domesticus) before and after moult and after testosterone treatment

In this study two experiments were run in parallel. To evaluate the possibl e influence of moult and age on differential white blood cell (WBC) counts, we captured juvenile and adult house sparrows (Passer domesticus) and hous ed them in outdoor aviaries. Blood was collected twice, before and after mo ult. Numbers of basophils, lymphocytes, and monocytes were higher in juveni les than in adults, whereas numbers of eosinophilic cells were similar in t he two age groups. Moult induced an increase in basophils and monocytes in both juveniles and adults. This indicates that moult and age impose differe nt immunological challenges on house sparrows. To evaluate the effect of te stosterone on differential WBC counts, some house sparrows in aviaries rece ived testosterone during the moult period. Testosterone administration redu ced, though not significantly, the number of all WBC types in juveniles, an d therefore appeared to have an nonspecific effect. However, the number of lymphocytes increased only in adults, which suggests a specific effect on t his cell type in this age group.