Fig. 8. Strouhal number as a function of flight speed in Glossophaga soricina. At speeds close to the theoretical minimum power speed (4-6 ms^-1) G. soricina operates with a Strouhal number associated with efficient lift and thrust production, 0.17<St<0.22. In the range 3.4-4 ms^-1 the Strouhal number is 0.25-0.4, which still is in a favourable region, but when V<3 ms^-1 the Strouhal number becomes higher (0.5<St<0.68), indicating that unsteady effects are important and that the production of lift and thrust is unfavourable.