Energy metabolism,body-temperature and breathing parameters in nontorpid blue-naped mousebirdsUrocolius macrourus

Summary Breathing frequencyF_r of resting blue-naped mousebirdsUrocolius macrourus lies between 50–70 per min and correlates directly with ambient temperatureT_a and energy metabolismM. The nocturnal mean energy intake per breath varies between 5.6–17.7 mJ/g. At highT_a the birds show gular fluttering with a relatively constantF_r of about 460 min^–1.M shows a constant absolute day-night difference of 25 J/g·h; the relative differences areT_a-dependent between 36–168% (lower values at lowerT_a). Thermal conductance is 2.10–2.15 J/g·h·°C (predicted 2.67), indicating a good insulation. Basal metabolic rate BMR is reduced by 63% compared to predicted values. At aT_a-range of +8–36 °C the birds are normothermic. Below this range nocturnalT_b andM decrease slightly with fallingT_a. The birds show partial heterothermia (shallow hypothermia). Clustering is an effective energy saving strategy which allows loweringM with keeping highT_b even at lowT_a.Oxygen-intake is controlled byF_r as well as by tidal volumeVt inT_a-dependent changing portions.VT can vary between 0.29–0.91 ml (mean value 49.7 ml).Abbreviations T_a ambient temperature - T_b body temperature - M energy metabolism - F_r breathing frequency - VT tidal volume - BMR basal metabolic rate - TNP thermoneutral point