Haematological variables are good predictors of recruitment in nestling pied flycatchers (<i>Ficedula hypoleuca</i>)

Abstract

:The number of different types of circulating leucocytes may provide information about the health state of birds in the wild. We counted the number and proportions of circulating leucocytes in blood smears of nestling pied flycatchers (Ficedula hypoleuca) shortly before fledging. We studied the relationship between these haematological measures and environmental factors like parasitism, body mass, hatching date, and brood size. The heterophils-to-lymphocytes ratio was higher in nestlings whose nests suffered from mite infestation and in lighter individuals, heterophils being the cells that responded preferentially to malnutrition. Recruited birds had lower lymphocyte and heterophil counts when nestlings than non-recruited ones. Our results show that heterophil count is a better predictor of local recruitment than other variables widely used for nestlings as survival predictors, like body mass or hatching date, supporting the hypothesis that low heterophil counts reflect a good individual health state in nestlings.