PATTERNS OF CUTANEOUS WATER EVAPORATION BY AUSTRALIAN PIGEONS

Abstract

We examined thermoregulation and cutaneous evaporative cooling by heat-stressed desert columbids (diamond dove, flock bronzewing, rock pigeon, and spinifex pigeon), temperate-zone columbids (common and brush bronzewing, and crested pigeon), and rainforest columbids (wonga pigeon, Luzon bleeding heart, and emerald dove). Body temperature at a T_a of 47 ºC was lower for desert birds (43.3 ºC) than for temperate-zone birds (43.6 ºC) and rainforest birds (44.4 ºC). Body-skin temperature difference (DT) was only 0.2 ºC for rainforest species; it was significantly higher at 0.4 ºC for temperate-zone pigeons, and significantly higher again at 0.9 ºC for arid-zone birds. Cutaneous water evaporation (CWE) was 2.1 mg H₂O cm^-2 h^-1 for rainforest species; it was significantly higher at 5.6 mg H₂O cm^-2 h^-1 for temperate-zone birds, and significantly higher again at 13.5 mg H₂O cm^-2 h^-1 for arid-zone pigeons. CWE of young wonga and bleeding heart pigeons was similar to that of adults, but was very high for young birds of other species. Comparisons at 42 ºC were very similar. Cutaneous evaporative cooling (CEC), which was suggested to be an evolutionarily recent mechanism compared to panting, is not effective for the three arboreal rainforest pigeons and probably did not occur in ancestral columbids that were presumably arboreal. We suggest that effective CEC evolved in altricial hatchlings of pigeons in a temperate-zone climate as a cooling mechanism, and has achieved its highest effectiveness in both young and adult desert pigeons.