Ecomorphological constraints imposed by the kidney component measurements in honeyeater birds inhabiting different environments

The histological renal anatomy of 10 species of honeyeaters was examined quantitatively, using stereology. The kidneys of five species of predominantly wet zone inhabiting birds: the western spinebillAcanthorhynchus superciliosus, White‐checked honeyeaterPhylidonyris nigra. New Holland honeyeaterPhylidonyris novaehollandiae, little wattlebirdanthochaera chrysopteraand red wattlebirdAnthochaera carunculata, were compared to five predominantly arid zone inhabiting birds: the grey‐fronted honeyeaterMeliphaga plumula, white‐plumed honeyeaterMeliphaga penicillata, white‐fronted honeyeaterPhylidonyris albifrons, spiny‐checked honeyeaterAcanthogenys rufogularisand yellow‐throated minerManorina flarigula.The kidneys were asymmetrical, with the left kidney being larger than the right kidney. Kidney mass was directly proportional to body mass (coefficient of correlation, r =+0·95), as was kidney volume to kidney mass (r =+1·0). Wet zone honeyeaters generally and a higher percentage and absolute volume of renal cortex, whilst arid zone honeyeaters generally had a significantly higher percentage and absolute volume of renal medulla. There were few differences between species, in either the percentage or absolute volume or luminal surface area of nephron components within the cortex. Within the medulla, wet zone honeyeaters generally had a higher percentage and absolute luminal surface area of collecting ducts, whilst arid zone honeyeaters had a higher percentage and absolute surface area of capillaries. This may be due to factors such as variations in diet and climate between habitats resulting in differences in honeyeater renal morphology which enable arid zone birds to conserve water and wet zone birds to conserve ions more efficiently.