ECOMORPHOLOGICAL CONSTRAINTS IMPOSED BY THE KIDNEY COMPONENT MEASUREMENTS IN HONEYEATER BIRDS INHABITING DIFFERENT ENVIRONMENTS

The histological renal anatomy of 10 species of honeyeaters was examin ed quantitatively, using stereology. The kidneys of five species of pr edominantly wet zone inhabiting birds: the western spinebill. Acanthor hynchus superciliosus, white-cheeked honeyeater Phylidonyris nigra. Ne w Holland honeyeater Phylidonyris novaehollandiae, little wattlebird A nthochaera chrysoptera and red wattlebird Anthochaera carunculata, wer e compared to five predominantly arid zone inhabiting birds: the grey- fronted honeyeater Meliphaga plumula, white-plumed honeyeater Meliphag a penicillata, white-fronted honeyeater Pkylidonyris albifrons, spiny- cheeked honeyeater Acanthogenys rufogularis and yellow-throated miner Manorina flavigula. The kidneys were asymmetrical, with the left kidne y being larger than the right kidney. Kidney mass was directly proport ional to body mass (coefficient of correlation, r = + 0.95), as was ki dney volume to kidney mass (r = + 1.0). Wet zone honeyeaters generally had a higher percentage and absolute volume of renal cortex, whilst a rid zone honeyeaters generally had a significantly higher percentage a nd absolute volume of renal medulla. There were few differences betwee n species, in either the percentage or absolute volume or luminal surf ace area of nephron components within the cortex. Within the medulla, wet zone honeyeaters generally had a higher percentage and absolute lu minal surface area of collecting ducts, whilst arid zone honeyeaters h ad a higher percentage and absolute surface area of capillaries. This may be due to factors such as variations in diet and climate between h abitats resulting in differences in honeyeater renal morphology which enable arid zone birds to conserve water and wet zone birds to conserv e ions more efficiently.