Letter | Published:

Vortex flow visualizations reveal change in upstroke function with flight speed in bats



The flapping wings of flying birds and bats generate complex, unsteady air movements. These consist of well-defined vortex structures which are a necessary result of the aerofoil action of the wings, and which transport momentum below and behind the animal in reaction to the lift force which both balances weight and provides thrust1. Visualization of the vortex patterns enables the aerodynamic function of the flapping wings to be determined2–6. Here we present the results of experiments with small vespertilionids which allow the first description of the vortex wake of bats. The aerodynamics of flapping flight is similar between birds and bats: thrust is always generated during the downstroke, but wingbeat gait (the cyclic pattern of wing movements) and the mechanical function of the upstroke are determined by wing morphology. We present the first evidence from aerodynamic experiments that in an individual bat or bat species, upstroke function and wingbeat gait also vary with flight speed, with aerodynamic lift being generated during the upstroke at high speeds but not during slow flight. This result confirms that flapping gaits are not species-specific, but are selected according to the mechanical conditions experienced by the animal.

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.


  1. 1

    Rayner, J. M. V. J. exp. Biol. 80, 17–54 (1979).

  2. 2

    Kokshaysky, N. V. Nature 279, 146–148 (1979).

  3. 3

    Spedding, G. R. Thesis, Univ. Bristol (1982).

  4. 4

    Spedding, G. R., Rayner, J. M. V. & Pennycuick, C. J. J. exp. Biol. 111, 81–102 (1984).

  5. 5

    Rayner, J. M. V. in Biona Report 5 (ed. Nachtigall, W.) 27–74 (Gustav Fischer, Stuttgart, in the press).

  6. 6

    Rayner, J. M. V. in Konstruktionsprinzipien lebender und ausgestorbener Reptilien. Konzepte SFB 230 4 (eds Riess, J. & Frey, E.) 89–118 (University of Tübingen, 1985).

  7. 7

    Rayner, J. M. V. in Recent Advances in the Study of Bats (eds Fenton, M. B., Racey, P. A. & Rayner, J. M. V.) (Cambridge University Press, in the press).

  8. 8

    Norberg, U. M. J. exp. Biol. 65, 179–212 (1976).

  9. 9

    Eisentraut, M. Z. wiss. Zool. 148, 159–188 (1936).

  10. 10

    Aldridge, H. D. J. N. Thesis, Univ. Bristol (1985).

Download references

Author information

Rights and permissions

To obtain permission to re-use content from this article visit RightsLink.

About this article

Further reading


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.