Body temperature and metabolism in the red-backed mousebird ( Colius castanotus) during fasting and torpor

Abstract

1. 1. Body temperature ( T b ) and metabolism ( M) of red-backed mousebirds ( Colius castanotus) fed ad libitum are in the same range as reported for other bird species of similar size (69 g). 2. 2. The interrelation between M (J/g-hr) and ambient temperature ( T a ) can be described by the formula M = 78.7− 1.63 T a . The thermal conductance varies from 2.1 to 2.5 J/g·hr·°C (predicted value 2.44). 3. 3. Sub-maintenance feeding leads to a gradual decrease of T b and M following the loss of body mass ( b.m.). The corresponding regression lines are: T b = −12.7 + 0.83 b.m. and M = −98.1 + 2.4 b.m. respectively. The thermal conductance decreased to more favourable values between 1.9 and 2.1 J/g-hr-°C due to a smaller difference of T b − T a . 4. 4. The relation between T b and M ( Q 10) was determined as 2.04–2.77 indicating that the decline in M closely follows physico-chemical conditions. 5. 5. After a long period of food deprivation and a loss of body mass of about 35%, the birds enter a state of torpidity. M of torpid birds may fall to less than 1/3 (on average) of basal levels depending on the actual T b reached after cooling. T b approximates T a with a critical level of about 18°C, below which no spontaneous arousal is possible and the birds fall in uncontrolled hypothermia.