White blood cells as indicators of adult condition and parental effort in European starlings, Sturnus vulgaris

Abstract

Parental care requires that substantial energy be allocated towards offspring that would potentially be used to maintain the adult’s own health. Female birds tend to provide most of the care, but a male’s assistance increases fledging success. The stress of parental care can take its toll on the bird with decreases in body condition and potential changes in parental effort. White blood cells (WBC) tend to increase in response to both stress and disease, and a high heterophil/lymphocyte (H/L) ratio in particular indicates stress in birds. This study aims to examine how WBC counts and H/L ratios vary with adult condition and parental effort in breeding European starlings (Sturnus vulgaris). European starlings are a facultatively polygynous passerine that typically exhibits social monogamy and bi-parental care. It was predicted that both WBC counts and H/L ratios would be negatively correlated with adult condition. It was also examined whether these two measures of stress were correlated with parental effort. WBC counts were not correlated with body condition or parental effort, but males tended to have lower counts than females. Males also tended to have lower H/L ratios than females. H/L ratios were negatively correlated with body condition in both sexes. H/L ratios were also not correlated with most forms of parental effort, but female H/L ratios tended to be negatively correlated with clutch size.