Previous studies have suggested that the haematocrit could be related to a number of factors within the bird´s biological cycle. In this study, the variations found in the haematocrit of Azure-winged Magpies Cyanopica during the reproductive period are analysed and related to factors such as age, sex, reproductive status, moult, month and study year. No among-years differences were detected. There were significant differences when different ages categories were compared. Nestlings presented lower values than juveniles and adults, but differences were not observed between the last two categories. In both sexes, a decreasing trend from March to June in the haematocrit was observed, although it was significant only for males and between these extreme months. There were not significant differences between helper and breeding males. High androgen levels (which stimulate erithropoyesis) in males at the onset of the reproductive period and their subsequent decline could explain the seasonal pattern observed. At the end of the reproductive period, no differences were found between those individuals who were moulting and those who were not.
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