Glycosylated Haemoglobin: A New Measure of Condition in Birds

The influence of condition on time of breeding and reproductive success has been discussed since Darwin first suggested a relation in 1871. We used a novel method to investigate the influence of condition on the timing of breeding and reproductive success by measuring a relatively inert physiological parameter-the amount of glycosylated haemoglobin-in blood samples taken from the collared flycatcher Ficedula albicollis. The percentage of glycosylated haemoglobin (%HbG) was assumed to be proportional to the average blood glucose level, during the 3-5 weeks before the blood sampling. The%HbG was influenced neither by sex nor age. Date of arrival at the breeding ground was negatively correlated with%HbG so that early-arriving birds had significantly higher%HbG than those arriving later. Clutch size, corrected for the effect of laying date, correlated positively with%HbG in females, as did the number of fledged young, corrected for the effect of laying date, for both sexes. We found no correlation between body mass and the%HbG. We suggest that prebreeding condition influences the timing of breeding and subsequent reproductive performance and that%HbG can be used as an indicator of prebreeding-condition in migrating birds.