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

• Published in: Canadian journal of zoology Vol. 76; no. 12; pp. 2235 - 2244
• Main Authors: HORAK, P, JENNI-EIERMANN, S, OTS, I, TEGELMANN, L
• Format: Journal Article
• Language: English
• Published: Ottawa, ON National Research Council of Canada 01.12.1998; Canadian Science Publishing NRC Research Press
• Subjects: Animal breeding; Biological and medical sciences; Birds; Breeding; Estrogens; Females; Fundamental and applied biological sciences. Psychology; Infectious diseases; Lymphocytes; Metabolites; Oxygen consumption; Parus major; Reproductive cycle; Thermoregulation. Hibernation. Estivation. Ecophysiology and environmental effects; Vertebrates: anatomy and physiology, studies on body, several organs or systems; Physiological condition; Plasma; Leukocyte; Metabolite; Sex; Parasite; Lipids; Metabolism; Protein; Reproduction; Vertebrata; Hematocrite; Aves; Parus major; Reproductive cycle
• ISSN: 0008-4301; 1480-3283; 1480-3283; 0008-4301
• DOI: 10.1139/cjz-76-12-2235

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. In both stages of the study, females had higher total leukocyte counts than males (Fig. lA). In spring, this difference was mainly due to the higher lymphocyte count of females (Fig. lB), while in summer, females had more circulating heterophiles than males (Fig. 1C), which also led to greater H/L ratios in breeding females than in males (Fig. ID). Since peripheral heterophilia is considered a characteristic symptom of almost any kind of stress (e.g., Maxwell 1993), inflammation (Parslow 1994), or microbial challenge (Rose et al. 1979; Hawkey et al. 1985), our results suggest that the state of health of breeding females during brood rearing was worse than that of males. The higher heterophile counts and H/L ratios in breeding females than in males was similar to the result obtained by Ots et al. (1998). It is possible that elevated H/L ratios indicate stress caused by intense reproductive effort, since Horak et al. (1998) found that H/L ratios in female great tits increased in response to experimental brood enlargement. In this context, it is interesting to note that during the prebreeding period, H/L ratios in males were higher than those in females (Fig. ID). Thus, if H/L ratios in great tits reflect stress in a similar manner to that found in poultry studies (e.g., Maxwell 1993), then our data suggest that males were more stressed than females during the prebreeding period, while females were more stressed during brood rearing. Possibly this sex difference relates to the additional workload imposed on females by brooding activities, in which males do not participate. The hematocrit values for male and female great tits did not differ during the prebreeding period, while females had remarkably higher hematocrit values than males during brood rearing. A high hematocrit is generally indicative of elevated oxygen consumption accompanying a high work load (Carpenter 1975). In birds, the hematocrit has been shown to increase in response to an experimental increase in flight costs in barn swallows (Saino et al. 1997a, 1997b) and brood enlargements in great tits (Horak et al. 1998). The higher hematocrit values in our brood-rearing females (see also Ots et al. 1998) can therefore be interpreted as indicating a higher work load for breeding females than for males. Analogously to several other studies (reviewed by Dawson and Bortolotti 1997b), our results do not support the notion of Sturkie (1986) that male birds have a higher hematocrit than females, as might be expected on the basis of androgenic stimulation and estrogen-induced suppression of erythropoiesis.