Effect of Dehydration on Cutaneous Water Evaporation in Heat-Exposed Pigeons (Columba livia)

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Abstract
The effect of water deprivation (dehydration) on cutaneous water evaporation (CWE, E,) was studied in seven heat-exposed rock pigeons (Columba livia). Dehydrated pigeons lost about 16% of the initial body mass after 48 h of water deprivation and additional heat exposure, resulting in a significant increase in hematocrit and serum sodium and chloride concentrations. Serum urea nitrogen concentration increased by 300%. These birds recovered almost all mass lost within 30 min of free access to water. At room temperature (30 C), was minimal (3.3 mg H₂O·cm⁻²·h⁻¹) during both normal hydration and dehydration. However, as ambient temperature increased to 45 and 50 C, increased to about 20 mg H₂O·cm⁻²·h⁻¹ in normally hydrated birds without concomitant panting. On the other hand, evaporation through the skin remained at its minimal level in heat-exposed dehydrated birds, and panting was apparently the major evaporative cooling mechanism. Skin and body temperatures were significantly higher in dehydrated versus normally hydrated, heat-exposed pigeons. Oxygen consumption was not affected by heat exposure in normally hydrated pigeons but significantly increased in dehydrated heat-exposed pigeons. This increase, combined with a decreased total water loss, resulted in a significantly reduced cooling ratio. Our data show that, in the normal hydration state, cutaneous evaporation accounts for almost all water loss. However, during dehydration respiratory water loss becomes the major cooling mechanism as a result of the resumption of panting.

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