Haematozoa infections in a Great TitParus majorpopulation in Central Portugal: relationships with breeding effort and health

Abstract

Blood parasites may act as modulators of their hosts’ ecology, life histories and fitness. We studied the prevalence ofPlasmodiumsp.,Haemoproteussp. andLeucocytozoonsp. and their effects on morphological, biochemical and haematological variables and on breeding effort of Great TitsParus major. Total prevalence (percentage of individuals infected by any parasite) ranged from 7.7% to 61.1%. There was an overall positive association in prevalence between the three haematozoan parasites. No effect of sex or age on infection status was observed. Negative impacts of infection on physiological condition depended largely on year and/or season and included effects on body condition index, plasma protein and haemoglobin index. There were also indications that parasite infection increased immune response and stress levels and activated antioxidant defence mechanisms. Males with higher fledging success had a higher probability ofHaemoproteusinfection, and females laying heavier eggs had a higher probability ofPlasmodiuminfection. However, clutch size was negatively associated with the probability of infection byLeucocytozoonandHaemoproteus. Surprisingly, males raising second broods had a lower prevalence of bothHaemoproteusandLeucocytozoon. Only 5.7% of first‐brood nestlings were infected, but those in infected nestboxes had a lower heterophil/lymphocyte ratio. This study confirms the pathogenicity of blood parasites to the host by demonstrating negative effects of infection on both physiology and breeding performance.