SEASONAL-CHANGES OF BLOOD VALUES IN THE ANDEAN MOUSE ABROTHRIX-ANDINUS

1. Bimonthly measurements of hematological indices were conducted in f reshly captured Abrothrix andinus (Rodentia:Cricetidae) over a period of one year. 2. All blood values were in the same range for adult male s and females, but juveniles showed lower red blood cell counts (RBC) and erythrocytes of larger size. 3. High RBC numbers, a slight but sig nificant increase of blood hemoglobin concentration (Hb), and a signif icant decrease in mean cell volume (MCV) were found during the winter months. 4. Hematocrit values (Hct) and the mean cell Hb concentration (MCHC) were relatively constant throughout the year. 5. Plasticity of MCV and an inverse correlation between size and the number of RBC may provide an enlarged diffusion area during winter. This mechanism appea rs to be a useful seasonal adjustment, since the increase of Hct and t he concurrent increase in blood viscosity are avoided.