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Nature 397, 651-653 (25 February 1999) | doi:10.1038/17687

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Bioenergetics:  One price to run, swim or fly?

R. McNeill Alexander1

It has long been accepted that it is metabolically cheaper for animals to fly than to run, and cheaper still for them to swim1. Measurements of oxygen consumption have shown, in comparisons between animals of equal mass, that the energy used by a mammal to run one kilometre is enough to enable a bird to fly about two kilometres, or a fish to swim up to ten kilometres.

  1. R. McNeill Alexander is in the School of Biology, University of Leeds, Leeds LS2 9JT, UK.