Black-bellied sandgrouse (Pterocles orientalis) and pin-tailed sandgrouse (Pterocles alchata): closely related species with differing bioenergetic adaptations to arid zones

Black-bellied sandgrouse had a mean resting metabolic rate (RMR) similar to the allometric prediction (5.53 mWg^-1 by day, 5.04 mWg^-1 at night; 97% and 110% of allometric prediction, respectively), whereas mean RMR in pin-tailed sandgrouse was lower than predicted (4.04 mWg^-1 by day; 62% of allometric prediction). Pin-tailed sandgrouse was the better thermoregulator, especially at high temperatures, with a well-developed evaporative cooling ability. At 40°C, evaporative heat loss (H_e) dissipated 89% of metabolic heat production (H_m), and at 25°C, H_e was 152% of the allometric prediction. This compares to 53% at 40°C and 101% at 25°C for black-bellied sandgrouse. However, both species had high lower and upper critical temperatures, and metabolism at high ambient temperatures (T_a's) was relatively insensitive to increasing temperature. Black-bellied sandgrouse showed greatly increased thermal conductance (C_d) at high temperatures facilitating nonevaporative heat loss. This species also demonstrated labile body temperature T_b) especially at low T_a, allowing energy savings under cooler conditions. -from Authors