Lower haematocrit, haemoglobin and red blood cell number in zebra finches acclimated to cold compared to thermoneutral temperature

Thermoregulation constitutes an important share of the energy budget of endotherms. Elevated thermoregulatory requirements must be met by oxygen supply through the blood, as heat is produced mainly via aerobic processes. In contrast to mammal studies, it remains unclear whether elevated thermoregulatory needs are followed by changes in haematological variables in birds. We investigated haematocrit (HCT), haemoglobin content per volume of blood (HGB), number of red blood cells (RBC), and size of the erythrocytes (RBC) in zebra finches (Taeniopygia guttata) acclimated to either cold or thermoneutral ambient temperatures under laboratory conditions. Seventy-nine females were maintained for six weeks either in cold (T = + 12 °C) or thermoneutral (T = + 32 °C) ambient temperature prior to blood collection. On average, HGB, HCT and RBC were significantly lower by about 10% in cold acclimated compared to thermoneutral acclimated birds. Only RBC was not different between the two acclimation tem...