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How swifts control their glide performance with morphing wings


Gliding birds continually change the shape and size of their wings1,2,3,4,5,6, presumably to exploit the profound effect of wing morphology on aerodynamic performance7,8,9. That birds should adjust wing sweep to suit glide speed has been predicted qualitatively by analytical glide models2,10, which extrapolated the wing’s performance envelope from aerodynamic theory. Here we describe the aerodynamic and structural performance of actual swift wings, as measured in a wind tunnel, and on this basis build a semi-empirical glide model. By measuring inside and outside swifts’ behavioural envelope, we show that choosing the most suitable sweep can halve sink speed or triple turning rate. Extended wings are superior for slow glides and turns; swept wings are superior for fast glides and turns. This superiority is due to better aerodynamic performance—with the exception of fast turns. Swept wings are less effective at generating lift while turning at high speeds, but can bear the extreme loads. Finally, our glide model predicts that cost-effective gliding occurs at speeds of 8–10 m s-1, whereas agility-related figures of merit peak at 15–25 m s-1. In fact, swifts spend the night (‘roost’) in flight at 8–10 m s-1 (ref. 11), thus our model can explain this choice for a resting behaviour11,12. Morphing not only adjusts birds’ wing performance to the task at hand, but could also control the flight of future aircraft7.

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Figure 1: Equilibrium gliding along a helical path.
Figure 2: Morphing swift wings can generate higher lift and lower drag than wings with a fixed geometry.
Figure 3: Morphing improves glide performance of swifts.
Figure 4: Morphing maintains wing structural integrity at high glide speeds.
Figure 5: Swifts roost at glide speeds that minimize energy expenditure.


  1. Rosén, M. & Hedenström, A. Gliding flight in a jackdaw. J. Exp. Biol. 204, 1153–1166 (2001)

    PubMed  Google Scholar 

  2. Tucker, V. A. Gliding birds: the effect of variable wing span. J. Exp. Biol. 133, 33–58 (1987)

    Google Scholar 

  3. Pennycuick, C. J. Gliding flight of the fulmar petrel. J. Exp. Biol. 37, 330–338 (1960)

    Google Scholar 

  4. Newman, B. G. Soaring and gliding flight of the black vulture. J. Exp. Biol. 35, 280–285 (1958)

    Google Scholar 

  5. Pennycuick, C. J. Wind-tunnel study of gliding flight in the pigeon Columba livia. J. Exp. Biol. 49, 509–526 (1968)

    Google Scholar 

  6. Müller, U. K. & Lentink, D. Turning on a dime. Science 306, 1899–1900 (2004)

    Article  Google Scholar 

  7. Weiss, P. Wings of change: shape-shifting aircraft ply future skyways. Sci. News 164, 359 (2003)

    Article  Google Scholar 

  8. Rayner, J. M. V. in Current Ornithology Vol. 5 (ed. Johnston, R. F.) 1–66 (Plenum, New York, 1988)

    Book  Google Scholar 

  9. Hoerner, S. F. & Borst, H. V. Fluid-dynamic Lift (Hoerner, Bakersfield, California, 1985)

    Google Scholar 

  10. Azuma, A. The Biokinetics of Flying and Swimming 2nd edn (AIAA Education Series, Reston, Virginia, 2006)

    Book  Google Scholar 

  11. Bäckman, J. & Alerstam, T. Confronting the winds: orientation and flight behaviour of roosting swifts, Apus apus. Proc. R. Soc. Lond. B 268, 1081–1087 (2001)

    Article  Google Scholar 

  12. Bruderer, B. & Weitnauer, E. Radarbeobachtungen über Zug und Nachtflüge des Mauerseglers (Apus apus). Rev. Suisse Zool. 79, 1190–1200 (1972)

    CAS  PubMed  Google Scholar 

  13. Parrott, G. C. Aerodynamics of gliding flight of a black vulture Coragyps atratus. J. Exp. Biol. 53, 363–374 (1970)

    Google Scholar 

  14. Nachtigall, W. Der Taubenflügel in Gleitflugstellung: geometrische Kenngrössen der Flügelprofile und Luftkrafterzeugung. J. Ornithol. 120, 30–40 (1979)

    Article  Google Scholar 

  15. Withers, P. C. An aerodynamic analysis of bird wings as fixed aerofoils. J. Exp. Biol. 90, 143–162 (1981)

    Google Scholar 

  16. Thomas, A. L. R. The flight of birds that have wings and tails: variable geometry expands the envelope of flight performance. J. Theor. Biol. 183, 237–245 (1996)

    Article  Google Scholar 

  17. Tucker, V. A. & Parrott, G. C. Aerodynamics of gliding flight in a falcon and other birds. J. Exp. Biol. 52, 345–367 (1970)

    Google Scholar 

  18. Bäckman, J. & Alerstam, T. Harmonic oscillatory orientation relative to the wind in nocturnal roosting flights of the swift Apus apus. J. Exp. Biol. 205, 905–910 (2002)

    PubMed  Google Scholar 

  19. Lack, D. Swifts in a Tower (Methuen, London, 1956)

    Google Scholar 

  20. Pennycuick, C. J. Flight of auks (Alcidae) and other Northern sea birds compared with Southern Procellariiformes: ornithodolite observations. J. Exp. Biol. 128, 335–347 (1987)

    Google Scholar 

  21. Ruijgrok, G. J. J. Elements of Airplane Performance (Delft Univ. Press, Delft, 1994)

    Google Scholar 

  22. Vogel, S. Life in Moving Fluids 2nd edn (Princeton Univ. Press, Princeton, 1994)

    Google Scholar 

  23. Schmitz, F. W. Aerodynamik des Flugmodells (C.J.E. Volckmann, Berlin, 1942)

    Google Scholar 

  24. Schlichting, H. Boundary Layer Theory 7th edn (McGraw-Hill, New York, 1979)

    MATH  Google Scholar 

  25. Videler, J. J., Stamhuis, E. J. & Povel, G. D. E. Leading-edge vortex lifts swifts. Science 306, 1960–1962 (2004)

    ADS  CAS  Article  Google Scholar 

  26. Hedenström, A. & Rosén, M. Predator versus prey: on aerial hunting and escape strategies in birds. Behav. Ecol. 12, 150–156 (2001)

    Article  Google Scholar 

  27. Veldhuis, L. L. M. Configuration and Propulsion Aerodynamics Research in the Low Speed Aerodynamics Laboratory [in Dutch] (Internal Report LSW 93–1, Faculty of Aerospace Engineering, Delft University of Technology, Delft, 1993)

    Google Scholar 

  28. Bird, J. D. Tuft-Grid Surveys at Low Speeds for Delta Wings (Technical Note D-5045, NASA, Hampton, Virginia, 1969)

    Google Scholar 

  29. Pennycuick, C. J., Alerstam, T. & Hedenström, A. A new low-turbulence windtunnel for bird flight experiments at Lund University, Sweden. J. Exp. Biol. 200, 1441–1449 (1997)

    CAS  PubMed  Google Scholar 

  30. Glutz von Blozheim, U. N. & Bauer, K. M. Handbuch der Vögel Mitteleuropas (Akademischer, Wiesbaden, 1980)

    Google Scholar 

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Swifts were supplied by Vogelopvang Woudenberg, Fugelpits Moddergat, Fugelhelling Ureterp, Vogelopvang De Strandloper Bergen, Vogelasiel De Wulp Den Haag, Vogelasiel Haarlem, Vogelasiel Naarden and Vogelopvang Someren. Swift photographs were provided by J.-F. Cornuet (front-view, Fig. 1a) and L.G.M. Schols (side-view Fig. 1a; Fig. 1b). N.G. Verhagen, J. Bäckman and J.H. Becking helped with background research. E.W. Karruppannan, L.J.G.M. Bongers, L. Molenwijk, L.M.M. Boermans, S. Bernardy and H. Schipper helped with the experimental set-up. F.T. Muijres and R. Petie helped with the experiments. T.P. Weber and S.M. Deban critically read the manuscript. O. Berg improved many versions of the manuscript. U.K.M. is funded by NWO, and A.H. by Carl Trygger’s Foundation.

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Correspondence to D. Lentink.

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This file contains Supplementary Figures 1-2 with Legends, Supplementary Table 1, Supplementary Equations , full protocol and additional references. (PDF 2016 kb)

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Lentink, D., Müller, U., Stamhuis, E. et al. How swifts control their glide performance with morphing wings. Nature 446, 1082–1085 (2007).

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