Haematological health assessment in a passerine with extremely high proportion of basophils in peripheral blood

Haematological methods are widely utilised among avian ecologists as a means for individual health assessment. However, the technical simplicity of some of the tests may easily lead to oversimplification of the evaluation. Here, we show in the Scarlet Rosefinch (Carpodacus erythrinus) that haematological parameters other than the widely used heterophil/lymphocyte (H/L) ratio may be important to investigate. We give the full description of seven basic haematological traits (leukocyte differential count, immature erythrocyte count, haematocrit, mean cell volume, total red and white blood cell count and blood parasite occurrence). Most remarkably, the examination of 178 adults and 155 nestlings has revealed that this species has an extraordinarily high proportion of basophils among the peripheral blood leukocytes (on average about 42 and 56%, respectively). Although the high basophil count is a general trait even in healthy individuals of this species, the proportion of these cells is condition-dependent and is further increased by Haemoproteus infection. Our results also suggest that the immature erythrocyte count in the peripheral blood is a good predictor of the nestlings’ growth rate. We conclude that the Rosefinch haematology differs strikingly from other avian species with known values of basic haematological parameters. We therefore emphasise the importance of a general haematological examination, based on material obtained by an appropriate method (e.g. for smear preparation, we recommend using differential staining and avoiding prior methanol fixation).