Heat production and body temperature of Arabian babblers (Turdoides squamiceps): A bird from hot desert habitats

The Arabian babbler (Turdoides squamiceps; adult body mass = 65-75 g) lives in groups all year round and inhabits extreme deserts. We measured body temperature (T_b) and resting metabolic rate (as O₂ consumption) and calculated thermal conductance of Arabian babblers at air temperatures (T_a) ranging between 11 and 44°C. T_b increased from 40°C to 42.9°C. The thermoneutral zone (TNZ) was found to occur at high air temperatures and was wide (31.6°C-40°C). The metabolic rate of 1.34 ml O₂ g^-1 h^-1 is half of that predicted for a passerine of its body mass. Allometric comparison with passerine species of up to 125 g body mass indicates that the resting metabolic rate (RMR) of babblers is about 71% of the basal metabolic rate (BMR) expected for a passerine of its body mass. When the RMR of the babblers was compared with the phylogenetically-adjusted equation for BMR of birds, RMR was only 73% of the value predicted from this equation. Its thermal conductance at a lower critical temperature of 31.6°C was 0.307 mW cm^-2°C^-1, which is 14.9% higher than that predicted for a bird of its body mass. The low heat production, the ability to tolerate high T_b, the wide TNZ at high T_a and high thermal conductance are physiological adaptations of Arabian babblers to extreme deserts.