“…For instance, Pennycuick [12] arrived at f ¼ K m 1=3 g 1=2 S À 1 A À 1=4 r À 1=3 air in which K is a numerical constant by finding the best fit to a set of bird data involving the following parameters: the bird mass m, the gravitational acceleration g, the wing span S, the wing area A, and the air density ρ air . Puranik et al [25] suggested f / mL À 2 B eff , where L is the wing span and B eff the effective wing breath defined as wing area divided by wing length, and found a good fit to data for both insects, birds, and bats. More recently, mathematically simpler expressions, e.g., a proportionality between mass to some power and wing/stroke frequency, have been considered [14,22,24,26].…”