Higher metabolic rates require higher oxygen supply to the mitochondria, which is facilitated by higher total haemoglobin content of blood (figures 2 and 3) or likewise by elevated haematocrit . In parallel with the shared increases in aerobic capacity in the pre-migratory phase, non-infected and infected hosts displayed significant increases in accumulated fuel (in the form of body fat) and increased breast muscles at similar rates leading up to this period.