Heat balance of the partridge Alectoris chukar exposed to moderate, high and extreme thermal stress.

1. The capacity of the chukar partridge, Alectoris chukar to withstand extreme environmental temperatures (up to 52 degrees C) was investigated. Under moderate conditions average resting values were: body temperature 40.7 degrees C, oxygen consumption (SMR) 0.74 ml O2 STP/g hr, evaporative water loss (EWL) between 1.28-4.02 mg H2O/g/hr and tidal volume (calculated) was 4.6-6.7 ml per breath. 2. At high air temperatures a rapid (582/min) shallow panting resulted in minute volume increase of about eight times, accompanied by twelve times augmentation in EWL. 3. Water evaporation reached 12.1 and 15.5 mg H2O/g/hr, these correspond with 162 and 182% of metabolic heat production at 45 and 48 degrees C Ta. 4. During long term exposure (270 min) to temperature extremes, birds could regulate Tb's of 43.7 and 44.7 degrees C at 45 and 48 degrees C respectively. No partridge could survive 270 min (r.h. = 10%) at 52 degrees C Ta. 5. The present study leads us to suggest that the partridge exposed to extreme heat stress cannot dissipate via water evaporation the entire heat which accumulates in the body. Therefore the bird has no choice but to use behavioral mechanisms, for dry heat dissipation. 6. The synchronized use of both evaporative and behavioral mechanisms may be essential for the partridge and its relatives, to withstand the extreme thermal stress prevalent in hot dry deserts.