Bundle, M.W.*; Dial, K.P.: The metabolic cost of flight in budgies: revisiting an outlier

Measuring the metabolic cost of flight has been possible for a little more than thirty years. Since V. A. Tucker’s classic work with budgerigars, fewer than a dozen other species of birds have been flown in wind tunnels in order to determine their metabolic rates during flight. Results from these studies portray one of two patterns: either the metabolic cost of flight appears to be independent of flight speed, or the cost of flight appears as a U-shaped curve with increasing flight speed. All but Tucker’s study show little increase in metabolic cost across the range of speeds for which data were obtained. In addition to the evidence provided by metabolic data, recent measurements of the mechanical power developed during flight also support the notion that birds are able to fly over a wide range of speeds with little change in the cost of flight. Flight costs in budgerigars should be viewed not as the commonly cited general rule, but rather as the exception. Since Tucker’s work stands in such stark contrast to nearly all of the available data on flight costs, we have revisited his experiments in our tunnel, increasing both the sample size and the range of speeds over which the birds have been flown. Four Budgerigars were flown across a range of speeds (4-16 m/s), while wearing a mask in order to collect and analyze their expired air. Our measurements of the metabolic cost of flight agree well with those of Tucker’s budgies. This confirmation of the original published pattern suggests that budgies are unlike other species and are unable to duplicate the unknown mechanism that allows other birds to fly with costs that are independent of flight speed. (supported by NSF IBN-0082075)