Editing Common ostrich (section)

=====Water intake and turnover=====

Common ostriches employ adaptive features to manage the dry heat and [[solar radiation]] in their habitat.  Ostriches will drink available water; however, they are limited in accessing water by being flightless. They are also able to harvest water through dietary means, consuming plants such as the ''[[Euphorbia heterochroma]]'' that hold up to 87% water.<ref name=Deeming />

Water mass accounts for 68% of body mass in adult common ostriches; this is down from 84% water mass in 35-day-old chicks. The differing degrees of water retention are thought to be a result of varying body fat mass.<ref name=Deeming /> In comparison to smaller birds ostriches have a lower evaporative water loss resulting from their small body surface area per unit weight.<ref name=zool241 />

When heat stress is at its maximum, common ostriches are able to recover evaporative loss by using a [[metabolic water]] mechanism to counter the loss by urine, feces, and respiratory evaporation.  An experiment to determine the primary source of water intake in the ostrich indicated that while the ostrich does employ a [[metabolic water]] production mechanism as a source of hydration, the most important source of water is food. When ostriches were restricted to the no food or water condition, the metabolic water production was only 0.5&nbsp;L·d<sup>−1</sup>, while total water lost to urine, feces, and evaporation was 2.3&nbsp;L·d<sup>−1</sup>. When the birds were given both water and food, total water gain was 8.5&nbsp;L·d<sup>−1</sup>. In the food only condition total water gain was 10.1&nbsp;L·d<sup>−1</sup>. These results show that the [[metabolic water]] mechanism is not able to sustain water loss independently and that food intake, specifically of plants with a high water content such as ''Euphorbia heterochroma'', is necessary to overcome water loss challenges in the common ostrich's arid habitat.<ref name=Deeming />

In times of water deprivation, urine [[electrolyte]] and [[osmotic concentration]] increases while urination rate decreases. Under these conditions [[urine]] [[solute]]:plasma ratio is approximately 2.5, or [[hyperosmotic]]; that is to say that the ratio of solutes to water in the plasma is shifted down whereby reducing osmotic pressure in the plasma. Water is then able to be held back from [[excretion]], keeping the ostrich hydrated, while the passed urine contains higher concentrations of solute. This mechanism exemplifies how renal function facilitates water retention during periods of dehydration stress.<ref name=zool241 /><ref name="Withers" />