BUNDLE, M/W*; DIAL, K/P; Rice University, Houston ; Univeristy Of Montana, Missoula: Power requirements of bird flight with additional mass
In the wild, birds routinely fly appreciable distances supporting the weight of prey items, nest material, water, and short-term fat stores. Under experimental conditions, subject animals are often encumbered with recording equipment (e.g. satellite transmitters, data loggers, etc) that artificially alters their body mass, and may also change the drag they experience at intermediate and fast flight speeds. From previous work we know that some birds are capable of takeoff and climbing flight while weighted with 150% of their bodyweight and can support 200% of their body weight during level flight. Yet surprisingly we have very little data documenting how this extra weight might alter the power required to remain airborn, and no empirical information addressing how these requirements may change with flight speed. To address these questions we trained three species of birds (Pica Hudsonia, Falco Sparverius and Nymphicus hollandicus) to fly in a variable speed windtunnel. We used in vivo sonomicrometry and measures of delto-pectoral strain to determine the pectoralis power output during free and encumbered flights across a wide range of speeds. During encumbered flights the birds supported the extra mass (approx. 0.1 Mb) and drag of a mask and tube that had previously been used to determine their metabolic power curves. For all three species, we found no difference in power requirements between free and encumbered flights at the minimum power speed. However at the fastest and slowest flight speeds from which measurements were possible, the power requirements were 38 � 9 % (� SE) and 26 � 5 % greater for encumbered vs. free flights. We discuss the physiological and ecological implications of these results.
