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Metabolic power, mechanical power and efficiency during wind tunnel flight by the European starling Sturnus vulgaris

S. Ward^1,*, U. Möller², J. M. V. Rayner³, D. M. Jackson¹, D. Bilo², W. Nachtigall² and J. R. Speakman¹

¹ Aberdeen Centre for Energy Regulation and Obesity, Department of Zoology, University of Aberdeen, Tillydrone Avenue, Aberdeen AB24 2TZ, UK,
² Institüt der Zoologie, Universität des Saarlandes, D-66041 Saarbrücken, Germany and
³ School of Biology, L.C. Miall Building, University of Leeds, Leeds LS2 9JT, UK

View larger version (14K): [in a new window]   Fig. 1. Time course of (A) the rates of oxygen consumption () and carbon dioxide production (), (B) metabolic power and (C) respiratory exchange ratio during a wind tunnel flight by starling 15 at 13.3 m s–1. Error bars show the standard error of four measurements made each minute (each of which was the mean value over 15 s). The printed symbols are larger than the error bars during most minutes. The bird flew for 12 min, starting at time 0. Metabolic rate increased when the bird was placed into the flight chamber immediately after the mask had been attached and when the bird was caught to remove the mask at the end of the measurement.

View larger version (14K): [in a new window]   Fig. 2. Metabolic power (Pmet) of two starlings during wind tunnel flight carrying a respirometry mask measured from the rates of oxygen consumption and carbon dioxide production [bird 15, , solid line Pmet=(2.03±12.6)V–1+(0.0013±0.0005)V3+(10.10±1.87); bird 19, , broken line Pmet=(59.0±27.7)V–1+(0.0020±0.0006)V3+(4.07±3.42)] (means ± S.E.M., N=24 for bird 15 and 21 for bird 19), where V is flight speed.

View larger version (14K): [in a new window]   Fig. 3. The proportion of each wind tunnel flight during which two starlings flew with consistent flapping flight in a steady position in the flight chamber, rather than alternating flapping and gliding flight (bird 15, , bird 19, ). The lines show the back-transformed relationships between arcsine(proportion of time spent in steady flight) (p) and flight speed (V) for each bird: bird 15, arcsinep=(1.86±0.34)–(0.148±0.034)V, r2=0.46, P<0.001; bird 19, arcsinep=(4.67±1.54)–(0.690±0.278)V+(0.032±0.012)V2, r2=0.39, P=0.015 (means ± S.E.M., N=24 for bird 15 and 21 for bird 19).

View larger version (9K): [in a new window]   Fig. 4. Respirometry mask and tube drag (D, mN) in relation to air speed (U, m s–1): D=(8.74±0.92)+(0.340±0.089)U (r2=0.83 %, P=0.032, mean ± S.E.M., N=5). See text for details.

View larger version (14K): [in a new window]   Fig. 5. Mechanical power (Pmech) for wind tunnel flight by two starlings carrying a respirometry mask, with Pmech estimated by two aerodynamic models (bird 15, vortex ring model ; bird 15, lifting line model ; bird 19, lifting line model ).

View larger version (15K): [in a new window]   Fig. 6. Flight muscle efficiency (EFM) of two starlings during wind tunnel flight (bird 15, Pmech estimated from the vortex ring model ; bird 15, Pmech estimated from the lifting line model ; bird 19, Pmech estimated from the lifting line model ), where Pmech is mechanical power.

View larger version (18K): [in a new window]   Fig. 7. Comparison of measured and predicted metabolic power (Pmet) for (A) bird 15 and (B) bird 19. Pmet was predicted for both birds from the lifting line model assuming a constant efficiency of 0.23 (LL, EFM=0.23) and a constant efficiency of 0.18 (LL, EFM=0.18) and for bird 15 from the vortex ring model assuming a constant efficiency of 0.23 (VR, EFM=0.23) and a constant efficiency of 0.18 (VR, EFM=0.18), where EFM is flight muscle efficiency.