Because we found infected and uninfected migratory birds to be indistinguishable in MMRs and exercise endurance and to share morphological adjustments commensurate with migratory preparation, we conclude that low-parasitaemia birds will have the same migratory capacity as uninfected individuals. Assuming flight speed is physiologically constrained by aerobic capacity, our results suggest that chronically infected migrants are able to fly at speeds similar to uninfected individuals and we do not expect differences in the duration of flight bouts. There is ambiguous evidence for haematozoan infections to affect migration in passerines: blood parasites can delay arrival on the breeding grounds of migrants  or they have no effect on arrival times . However, arrival might mainly be determined by factors other than flight speed because migrants usually spend more than 80% of total migration time at stopover sites . Thus, infected and uninfected individuals can still differ in the timing of migration if, e.g. the efficiency of fundamental stopover behaviour like foraging and fuelling is hampered by the parasite and results in a later departure in infected birds than their non-infected counterparts.