Heat balance of acclimated pigeons (Columba livia) exposed to temperatures up to 60°c ta

1. 1. Hand-reared acclimated (Acc) and nonacclimated (NAcc) rock pigeons Columba livia were exposed to ambient temperatures (Ta) of 30-65°C and low relative humidities (RH) of 5-35%. 2. 2. Resting heat production of 3.6 ± 0.7 cal g ^-1 hr^-1 (31.7 W/m²) and 4.9 ± 0.8 cal g ^-1 hr ^-1 (43.0 W/m²) were measured in Ace and NAcc pigeons, respectively. 3. 3. The total evaporative water loss (EWL) was significantly lower (P < 0.05) in Acc compared to NAcc; EWL increase of 0.7 mg H₂O per 1°C rise in Ta and 1.35 mg H₂O/1°C Ta, respectively, were calculated during heat exposure to 35-60°C Ta. 4. 4. At 60°C Ta, acclimated pigeons dissipated 304% of heat production as latent heat. In Acc birds body temperature was regulated between 41.2 and 42.0°C within the thermoneutral zone (TNZ) (30-60°C). 5. 5. In NAcc pigeons the TNZ extends only between 30 and 42°C Ta. When Ta was increased from 35-45°C hyperthermia developed at 0.11°C/1°C increase in Ta. 6. 6. The heat acclimated pigeon effectively uses cutaneous evaporation instead of panting and gular fluttering for dissipation of both metabolic heat and ambient heat influx. 7. 7. The significance of the skin and the feather coat in the adaptation of birds to life in the hot deserts is discussed.