The metabolic power requirements of flight and estimations of flight muscle efficiency in the cockatiel (Nymphicus hollandicus)

Abstract

SUMMARYLittle is known about how in vivo muscle efficiency, that is the ratio of mechanical and metabolic power, is affected by changes in locomotory tasks. One of the main problems with determining in vivo muscle efficiency is the large number of muscles generally used to produce mechanical power. Animal flight provides a unique model for determining muscle efficiency because only one muscle, the pectoralis muscle, produces nearly all of the mechanical power required for flight. In order to estimate in vivo flight muscle efficiency, we measured the metabolic cost of flight across a range of flight speeds (6-13ms -1 ) using masked respirometry in the cockatiel (Nymphicus hollandicus) and compared it with measurements of mechanical power determined in the same wind tunnel. Similar to measurements of the mechanical power-speed relationship, the metabolic power-speed relationship had a U-shape, with a minimum at 10ms -1 . Although the mechanical and metabolic power-speed relationships had similar minimum power speeds, the metabolic power requirements are not a simple multiple of the mechanical power requirements across a range of flight speeds. The pectoralis muscle efficiency (estimated from mechanical and metabolic power, basal metabolism and an assumed value for the 'postural costs' of flight) increased with flight speed and ranged from 6.9% to 11.2%. However, it is probable that previous estimates of the postural costs of flight have been too low and that the pectoralis muscle efficiency is higher.

Hovering performance of Anna's hummingbirds ( Calypte anna ) in ground effect

“…Altshuler et al [34] proposed that hummingbirds use their tails to deflect the flow created by the wings in order to maintain pitch stability Figure 6. Comparison of average weight-normalized mechanical power estimates for Anna's hummingbirds with theoretical estimates derived from two helicopter models for hovering in ground effect (IGE) and out of ground effect (OGE) ( [28,29]; as cited in [1,2]), with vertical thrust assumed to be constant. Error bars correspond to + 1 s.d.…”

Flight metabolism in relation to speed in Chiroptera: Testing the U-shape paradigm in the short-tailed fruit batCarollia perspicillata

“…This ratio is not necessarily constant over a range of flight speeds, but has the potential to vary with changing wing kinematics, aerodynamic gait, flight mode or muscle efficiency [e.g. intermittent flight in birds reduces the metabolic flight cost (Rayner, 1986;Rayner, 1994;Rayner, 1999); bird pectoralis efficiency changes with flight speed (Morris et al, 2010)]. Based on the theoretical prediction, the mechanical efficiency of C. perspicillata at the minimum power speed is ~12%, close to values previously reported for flying vertebrates.…”

“…Mechanical efficiencies of flying vertebrates are most frequently calculated from metabolic data obtained using respirometry combined with mechanical power estimated from theory (e.g. Bernstein et al, 1973;Dudley and Winter, 2002;Thomas, 1975;Tucker, 1972;Ward et al, 2001), with few authors attempting to employ mechanical power measurements made directly from the flight musculature (but see Morris et al, 2010). These direct measurements yield a lower mechanical power output than the calculations based on aerodynamic theory.…”

Muscle function during takeoff and landing flight in the pigeon (Columba livia)

“…Once aloft, aerodynamic theory (e.g. Morris and Askew, 2010a;Pennycuick, 1968;Rayner, 1979), mechanical power measurements Morris and Askew, 2010b;Tobalske et al, 2003) and measurements of metabolic rate (Bundle et al, 2007;Morris et al, 2010;Tucker, 1968) suggest that flying at low speed requires greater aerodynamic power. Acceleration following takeoff to increase forward flight speed also requires a greater forward component of aerodynamic force than steady flight.…”