High glucose concentrations are associated with symptoms of mild anaemia in Whiskered Terns: consequences for assessing physiological quality in birds

Although blood concentrations of glucose and haemoglobin are known to correlate with nutritional state of individuals, hyperglycaemic states in vertebrates are often linked to anaemia. A negative relationship between blood concentrations of glucose and haemoglobin was confirmed in a wild population of Whiskered Terns Chlidonias hybrida. Also, terns with higher haemoglobin concentrations initiated laying earlier and had clutches with larger eggs, while blood glucose concentrations of individuals were not associated with the timing of laying and egg size. This implies that blood haemoglobin concentration may be considered a much more robust indicator of physiological quality than glucose concentrations in the Whiskered Tern, and possibly in other waterbirds.