THE COOLING POWER OF THE PIGEON HEAD

Resting pigeons preheated to a stable core temperature of 43.2 °C, which is within the range of body temperatures recorded during flight, were able to cool their body at high rates if their head and upper neck were exposed to an air stream at 23.5 °C. The heat dissipation capacity of the head and neck, estimated from measurements made at a wind speed (100 km h-1) corresponding to fast flight, was 9.8 W, or 4.5 times the resting heat production. Since the greater part of this capacity, about 8 W, was attributable to the inner surfaces of the mouth, ram ventilation of the buccal cavity appears to be an important mechanism for increasing evaporative heat loss during flight. Accordingly, wind-assisted mouth cooling should be utilized by resting pigeons, since exposure to a slight breeze (approximately 10 km h-1) could augment their dissipating power by an amount equivalent to their resting metabolic rate. It is concluded that beak opening, together with a source of convection other than panting and gular flutter, is required to exploit fully the heat dissipation capacity of the buccopharyngeal mucosa of birds.