Abstract

Simple Summary: This study explored how blood parasites, known as haemosporidians, impact the oxidative status of Rufous-collared Sparrows, a common bird species in Chile. Oxidative status measures the balance between harmful molecules called reactive oxygen species (ROS) and the bird's ability to neutralize them with antioxidants. The study found that birds infected with haemosporidians had higher levels of ROS, indicating more oxidative stress than uninfected birds. While the overall antioxidant levels did not differ between infected and uninfected birds, the infected birds showed a greater imbalance in ROS/TAC, suggesting they suffered more oxidative damage. This was especially true for birds in their reproductive phase. These findings suggest that haemosporidian infection, combined with the demands of reproduction, may impose significant health costs on these birds. Understanding this could help us learn more about how infections affect wildlife, and the strategies parasites use to survive in their hosts. Haemosporidians are common blood parasites in wild bird populations, yet their effects on oxidative status remain understudied. Here, we measured the levels of thiobarbituric acid-reactive substances (TBARS) as an indicator of reactive oxygen species (ROS), total antioxidant capacity (TAC) as an indicator of non-enzymatic molecular antioxidants, and TBARS/TAC ratio as an indicator of oxidative status. We also used parasite genus-specific primers and PCR techniques to detect haemosporidians in 117 adults of Rufous-collared Sparrow (Zonotrichia capensis) from four locations in south-central Chile. Mixed-effect models were employed to compare oxidative indicators between infected and uninfected birds. Infected birds showed significantly higher TBARS levels, but no significant differences in TAC, leading to a higher TBARS/TAC ratio, especially in reproductive individuals. This suggests increased oxidative damage in infected birds, irrespective of sex or body condition. A positive relationship between TBARS and TAC was observed in both groups, but the antioxidant response was weaker in infected birds, indicating differential oxidative stress responses based on infection status. Body condition did not differ significantly between infected and uninfected individuals. These results demonstrate that haemosporidian infections impose oxidative costs on birds, potentially compounding the oxidative costs associated with reproduction.