Growth profile variation among altricial bird species is reflected in variation in development patterns of parameters influencing blood oxygen carrying capacity (O 2 Cap). Rainbow bee-eater nestlings develop slowly and their asymptotic mass reaches or exceeds adult levels before undergoing prefledging recession (mass overshoot–recession profile, MOR). Erythrocyte count (RBC), blood hemoglobin content (Hb) and hematocrit (Hct) increased 2.5-fold during development. Hatchlings’ erythrocyte volume closely approximated adult levels and decreased by only 1% during development. Erythrocyte hemoglobin content and concentration also increased minimally. RBC and Hb increased throughout development, but Hct increase was restricted to early development, overlapping the mass-gain period by just 37%. Blood parameters influencing O 2 Cap did not exceed adult levels and then decline during the mass asymptote–recession development stage. Continuing increase in RBC and Hb at this stage contributed to attaining a fledging O 2 Cap of adult levels. Results were consistent with there being a common mechanism regulating developmental increase in O 2 Cap in altricial birds. However, features of this development in bee-eater nestlings variously conformed to the patterns of both species with MOR and species with standard growth profiles. Some features shared with other MOR species also differed in timing or pattern in bee-eater nestlings.
Australian Journal of Zoology – CSIRO Publishing
Published: Mar 23, 2006