Thermal conductance in birds and mammals

1. 1. Thermal conductance (C measured in cal.g^-1 hr^-1 °C^-1) in birds, mammals and lizards is exponentially related to body weight (W measured in g). The equation developed for thirty-one species of birds is log C = 0·662 - 0·536 log W while the relationship for twenty-four species of mammals is log C = 0·691 - 0·505 log W. There is no significant difference between these curves. 2. 2. Conductance of varanid lizards is ten times higher than for intact birds and mammals and four times higher than defeathered birds. The high conductance of lizards is partly because measurements were made in an air stream up to 300 cm/sec and because of their large skin surface. 3. 3. Heat loss in defeathered birds is two to three times higher than in intact birds. The greatest increase in conductance occurred in the larger birds, suggesting the greater insulation of the large birds partly resides in the feathers.