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.
Your institute does not have access to this article
Open Access articles citing this article.
Nature Open Access 09 March 2022
Scientific Reports Open Access 13 May 2020
Nature Communications Open Access 01 March 2016
Subscribe to Journal
Get full journal access for 1 year
only $3.90 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Tax calculation will be finalised during checkout.
Get time limited or full article access on ReadCube.
All prices are NET prices.
Rosén, M. & Hedenström, A. Gliding flight in a jackdaw. J. Exp. Biol. 204, 1153–1166 (2001)
Tucker, V. A. Gliding birds: the effect of variable wing span. J. Exp. Biol. 133, 33–58 (1987)
Pennycuick, C. J. Gliding flight of the fulmar petrel. J. Exp. Biol. 37, 330–338 (1960)
Newman, B. G. Soaring and gliding flight of the black vulture. J. Exp. Biol. 35, 280–285 (1958)
Pennycuick, C. J. Wind-tunnel study of gliding flight in the pigeon Columba livia. J. Exp. Biol. 49, 509–526 (1968)
Müller, U. K. & Lentink, D. Turning on a dime. Science 306, 1899–1900 (2004)
Weiss, P. Wings of change: shape-shifting aircraft ply future skyways. Sci. News 164, 359 (2003)
Rayner, J. M. V. in Current Ornithology Vol. 5 (ed. Johnston, R. F.) 1–66 (Plenum, New York, 1988)
Hoerner, S. F. & Borst, H. V. Fluid-dynamic Lift (Hoerner, Bakersfield, California, 1985)
Azuma, A. The Biokinetics of Flying and Swimming 2nd edn (AIAA Education Series, Reston, Virginia, 2006)
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)
Bruderer, B. & Weitnauer, E. Radarbeobachtungen über Zug und Nachtflüge des Mauerseglers (Apus apus). Rev. Suisse Zool. 79, 1190–1200 (1972)
Parrott, G. C. Aerodynamics of gliding flight of a black vulture Coragyps atratus. J. Exp. Biol. 53, 363–374 (1970)
Nachtigall, W. Der Taubenflügel in Gleitflugstellung: geometrische Kenngrössen der Flügelprofile und Luftkrafterzeugung. J. Ornithol. 120, 30–40 (1979)
Withers, P. C. An aerodynamic analysis of bird wings as fixed aerofoils. J. Exp. Biol. 90, 143–162 (1981)
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)
Tucker, V. A. & Parrott, G. C. Aerodynamics of gliding flight in a falcon and other birds. J. Exp. Biol. 52, 345–367 (1970)
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)
Lack, D. Swifts in a Tower (Methuen, London, 1956)
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)
Ruijgrok, G. J. J. Elements of Airplane Performance (Delft Univ. Press, Delft, 1994)
Vogel, S. Life in Moving Fluids 2nd edn (Princeton Univ. Press, Princeton, 1994)
Schmitz, F. W. Aerodynamik des Flugmodells (C.J.E. Volckmann, Berlin, 1942)
Schlichting, H. Boundary Layer Theory 7th edn (McGraw-Hill, New York, 1979)
Videler, J. J., Stamhuis, E. J. & Povel, G. D. E. Leading-edge vortex lifts swifts. Science 306, 1960–1962 (2004)
Hedenström, A. & Rosén, M. Predator versus prey: on aerial hunting and escape strategies in birds. Behav. Ecol. 12, 150–156 (2001)
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)
Bird, J. D. Tuft-Grid Surveys at Low Speeds for Delta Wings (Technical Note D-5045, NASA, Hampton, Virginia, 1969)
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)
Glutz von Blozheim, U. N. & Bauer, K. M. Handbuch der Vögel Mitteleuropas (Akademischer, Wiesbaden, 1980)
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.
Reprints and permissions information is available at www.nature.com/reprints. The authors declare no competing financial interests.
About this article
Cite this article
Lentink, D., Müller, U., Stamhuis, E. et al. How swifts control their glide performance with morphing wings. Nature 446, 1082–1085 (2007). https://doi.org/10.1038/nature05733
Investigation of static wings interacting with vertical gusts of indefinite length at low Reynolds numbers
Experiments in Fluids (2022)
Science China Technological Sciences (2021)
Morphological variability of Argynnis paphia (Lepidoptera: Nymphalidae) across different environmental conditions in eastern Slovakia
Scientific Reports (2020)