IMPOSITIONS ON ENERGY BALANCE IN PROLONGED FLIGHT: WIND-TUNNEL MEASUREMENTS WITH “MODEL BIRDS"

ABSTRACT

Metabolic and thermoregulatory aspects of prolonged wind-tunnel flights of pigeons (Columba livia) are presented. Measurements and calculations of mass rates, gas volumes, and heat loss are given in a detailed table. The wind tunnel and the testing and training procedures are described. Metabolic power and respiratory exchange rates are given as functions of flight time within the first hour of flight; boundary conditions are body mass, feeding, and seasonal conditions. The changes were drastic, but metabolic power during the first hour of flight was only 3% higher than any succeeding hour. Mass loss and evaporative water loss at different ambient temperatures are given as functions of flight time within the first hour. Idealized time plots of fuel consumption, metabolic water production, and mass losses are derived from these functions. Heat loss due to metabolic water loss accounted for 9%, and nonevaporative heat loss, to 77% of total heat loss; therefore 14% was due to body water loss at the ambient temperature of 20 °C. Maximum flight times and maximum flight distances are calculated for different ambient temperatures and defined percentages of body water loss. Analytical expressions are given for metabolic power and body mass loss as functions of flight speed, as well as metabolic power as functions of body mass and ambient temperatures. Finally, the limits of power output in the power-speed-mass-temperature range are shown in a graphical and numerical comparison.