Bird populations are declining worldwide, with habitat loss and climate change often cited as major factors; however, the role of disease remains less understood. Avian blood parasites, including Plasmodium, Haemoproteus, and Leucocytozoon, are widespread and can negatively affect host physiology by causing anemia, altering immune function, and increasing stress. Birds are frequently infected with multiple parasite species simultaneously (co-infections), which may intensify these effects, particularly during energetically demanding periods such as migration. This study investigates the physiological impacts of blood parasite co-infections in wild birds by examining multiple condition metrics, including hemoglobin, hematocrit, blood glucose and fat score, to better understand how co-infection influences overall host health.