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First published online February 12, 2007
Journal of Experimental Biology 210, 741-749 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.02705
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Cloacal evaporation: an important and previously undescribed mechanism for avian thermoregulation

Ty C.M. Hoffman*, Glenn E. Walsberg and Dale F. DeNardo

School of Life Sciences, Arizona State University, Tempe, AZ 85287-4501, USA


Figure 1
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  		Fig. 1. Rates of evaporation measured in Inca doves at four ambient temperatures. During `Sealed' trials cloacae were occluded with cyanoacrylic glue; during `Unsealed' trials cloacae were not occluded. Relative humidity of the head-compartment influent was near 0% during `Dry' trials and near 100% during `Wet' trials. The differences between non-buccopharyngeal traces for `Unsealed' and `Sealed' trials indicate rates of cloacal evaporation. Those differences (and therefore the rates of cloacal evaporation) were negligible at Ta≤40°C and significant at Ta=42°C. The differences between traces for `Dry' and `Wet' trials indicate compensatory adjustment of cutaneous evaporation; the differences were non-significant at all four ambient temperatures. Values shown are means ± s.e.m. (N=7–13).

 

Figure 2
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  		Fig. 2. Average apportionment of total evaporation in Inca doves at 42°C. Buccopharyngeal and non-buccopharyngeal evaporation were directly and separately measured. Cutaneous evaporation was defined as the whole of non-buccopharyngeal evaporation during `Sealed' trials, in which cloacae were occluded. Cloacal evaporation was calculated as non-buccopharyngeal evaporation during `Unsealed' trials minus non-buccopharyngeal evaporation during `Sealed' trials. Values in parentheses indicate average rates of evaporative heat loss.

 

Figure 3
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  		Fig. 3. The ratio of volumetric rate of buccopharyngeal evaporation to volumetric rate of oxygen consumption in Inca doves at four ambient temperatures. This evaporespiratory ratio was nearly quadrupled as ambient temperature increased from 30° to 42°C, indicating that birds were elevating buccopharyngeal evaporation above rates that would occur just as a result of breathing. There is no statistical difference between traces for `Unsealed' and `Sealed' trials. Values shown are means ± s.e.m. (N=8–12).

 




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