Health and reproduction: the sex-specific clinical profile of great tits (Parus major) in relation to breeding

Abstract

To describe the changes in clinical profile of individuals that occur during different stages of the reproductive cycle, 17 condition indices including leukocyte counts, plasma protein and metabolite concentrations, hematocrit, and hemoparasite prevalence were examined in prelaying and brood-rearing great tits (Parus major). The metabolic profile pointed to increased fat metabolism during the prebreeding period. Protein metabolism did not indicate nutritional limitation. Prelaying birds had elevated gamma-globulin levels, which may indicate either greater investment in humoral immune defence or, alternatively, greater exposure to immune challenge than for breeders. The sexes did not differ with respect to prevalence of hemoparasites, but females had generally lower albumin/globulin ratios than males, which might indicate a greater predisposition to infectious diseases. Breeding females had higher hematocrit values and heterophile/lymphocyte ratios than males, suggesting that brood rearing imposes a greater work load and exerts greater stress on females. In contrast to the breeding period, males seemed to be more stressed than females prior to egg laying, as indicated by their lower lymphocyte counts and higher heterophile/lymphocyte ratios.