Three issues concerning avian peripheral blood glucose concentrations that require more investigation are: (a) whether they are as variable and high in free-living as in captive and domesticated adults, (b) the sources of variation in adult concentrations and (c) if and how they change during nestling development. Whole blood glucose concentrations (B(Glu)) of wild adults of four native passerine and one exotic dove species varying in mass and diet were measured in south-east Australia. There was significant inter-specific variation in B(Glu), but the range in mean values (11.1 to 17.0 mmol L(-1)) conformed with that published for many adult captive and domestic birds of similar size and was well above that for adult mammals of comparable mass. B(Glu) also varied markedly intra-specifically in four species (coefficients of variation 17.5-32 ). Trapping procedure and timing of sampling did not explain this variation, but adult body mass was associated with B(Glu) in two species. If whole blood haemoglobin concentrations (Hb) reliably reflect body condition, most of the adults sampled were in good condition. Wild nestling Welcome swallows (Hirundo neoxena) and Spotted doves (Streptopelia chinensis), respectively, underwent 20 and 40 continuous, linear, developmental increases in B(Glu). Swallows fledged with a mean B(Glu) 23 greater than, and doves with a mean similar to, that of adults. The developmental increase probably reflected an increase in metabolic rate as nestlings gained mass and became more active.