Stress protein levels and blood parasite infection in blue tits (Parus caeruleus): a medication field experiment

It has been suggested that blood parasites are a source of physiological stress for avian hosts in the wild. We report the first experimental evidence relating blood parasite infection to the physiological stress response in a wild avian population. We reduced through medication the intensity of infection by Haemoproteus majoris and the prevalence of infection by Leucocytozoon majoris in half of a sample of female blue tits (Parus caeruleus). Results show that (i) control females had a higher final level of the stress protein HSP60 than medicated ones, (ii) the initial immunoglobulin level was negatively correlated with final HSP60 level, (iii) control females had a lower final body mass than medicated ones, body mass being negatively correlated with the number of blowfly pupae in the nest only for control females, and (iv) final female body mass was positively correlated with nestling tarsus length only for control females, which produced nestlings with shorter tarsi than medicated females. Responses of HSPs to parasitism, and associations with aspects of immune function and condition, suggest that the stress response may allow blue tits to maintain blood parasites under control during reproductive stress.