Wingbeat frequencies were observed in the field for 32 morphologically diverse bird species, representing 18 families, and ranging in mass from 20 g to nearly 5 kg. A combination of multiple regression and dimensional analysis was used to show that wingbeat frequency (f) may be estimated by:
f = 1.08(m1/3g1/2b−1S−1/4p−1/3
where m is the bird's body mass, g is the acceleration due to gravity, b is the wing span, S is the wing area and p is the air density. The predicted wingbeat frequency can be used to estimate the power available from a bird's flight muscles, and an estimate of the power required to fly can be obtained for comparison from the computer programs of Pennycuick (1989a). Field observations of airspeed are given for 30 of the 32 species. These are combined with the observations of wingbeat frequency to estimate wingbeat wavelength, and the ratio of wavelength to wing span, which is closely related to the ‘advance ratio’ as used by Ellington (1984).