Figure 5.
Bipedal stability in birds. (a) Comparison of mean (±s.d.) value of 
for each species studied. Species with a mean value of 
(white bars) ubiquitously demonstrated a pattern of decreasing w* with increasing S*. (b) Bipedal stability is influenced by the length of the legs (or equivalently, hip height) relative to body mass. For a point mass m on a massless leg of length l1 or l2 (where l2 > l1), the mass with leg length l2 exerts a greater moment (by virtue of weight) about the base of support than the mass with leg length l1, for the same leg orientation α. Therefore, it is easier for the mass to be shifted away from a stable state and tipped over (i.e. relatively longer legs decrease stability).