Water turnover and body water distribution during dehydration in a large arid-zone bird, the Emu,Dromaius novaehollandiae

Summary

The emu is a large flightless bird (body mass, BM, about 40 kg), whose range extends into the arid regions of Australia. Its water relations were studied by examining the water turnover and the distribution of body water before and after 9 days of water restriction, when only dry feed was provided. Initially water turnover was 44.8 ml kg⁻¹ d⁻¹ but with restriction of intake water balance was not maintained. Although efflux was reduced to 14.8 ml kg⁻¹ d⁻¹ the net water loss was still about 7 ml kg⁻¹ d⁻¹.

Total body water was 61% of body mass (ml H₂O/100 gBM) in both hydrated and dehydrated emus. The initial distribution of water was: plasma volume 5.0% BM, interstitial volume 39.1% BM. Gut water content was 7.6% BM in wild emus. During dehydration the interstitial space lost the most water, contributing 54.5% of the total loss compared with 36.4% from cells and gut. Calculations indicate that the emu can remain in water balance without drinking only if its food has a high water content and water is not required for thermoregulation.