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 (Tb) and resting metabolic rate (as O2consumption) and calculated thermal conductance of Arabian babblers at air temperatures (Ta) ranging between 11 and 44°C. Tbincreased 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 O2g−1h−1is 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 Tb, the wide TNZ at high Taand high thermal conductance are physiological adaptations of Arabian babblers to extreme deserts.