Abstract
Parent birds often have substantial fat reserves that are critical in successful breeding. Erythrocyte variables, particularly haematocrit and haemoglobin concentration in peripheral blood, are increasingly being used as avian body-condition indices (BCIs) but problems can arise if such variables are used and interpreted uncritically. We investigated whether there were significant relationships between three size-adjusted BCIs thought to reflect the magnitude of fuel reserves, and four erythrocyte variables in free-living, adult Welcome Swallows (Hirundo neoxena) in south-eastern Australia over two breeding seasons. Haematocrit was not correlated with body-mass and condition. Whole-blood haemoglobin concentration, mean cell haemoglobin concentration and haematocrit-haemoglobin residuals were significantly related to body-mass and all the BCIs but the correlations were modest and negative (r ≤—0.39). Thus none of the erythrocyte variables was convincing as a reliable indicator of estimated fuel reserves in breeding adults. Currently the utility of haematocrit and haemoglobin concentration as reliable BCIs in adult birds cannot be assumed and needs to be validated for each population or species being investigated.
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