To our knowledge, this is the first functional investigation of one-legged standing in flamingos to explore both musculoskeletal anatomy and behaviour. We investigated two aspects of postural stability that can exact high muscle forces: body weight support and maintaining balance. Here, we examined whether it is possible for flamingos to stand on one leg with minimal active muscle forces. While increased energy cost for generating muscle contractile forces could negate any benefits from reducing muscle fatigue or heat loss, whether high levels of muscle activity are required for a flamingo to stand on one leg is unknown. Conversely, the heat loss hypothesis assumes that the energetic cost of activating muscles for the one-legged stance is smaller than any heat savings realized. The muscle fatigue hypothesis assumes that standing for long periods requires sufficiently high levels of active contractile force that would fatigue muscle, necessitating alternating stance from one leg to the other. Why do flamingos stand on one leg? Flamingos are thought to stand on one leg to reduce muscle fatigue or heat loss. Taken together, our results highlight the possibility that flamingos stand for long durations on one leg without exacting high muscular forces and, thus, with little energetic expenditure. Second, we discovered that live flamingos standing on one leg have markedly reduced body sway during quiescent versus alert behaviours, with the point of force application directly under the distal joint, reducing the need for muscular joint torque. Our results suggest that flamingos engage a passively engaged gravitational stay apparatus (proximally located) for weight support during one-legged standing.
By contrast, the cadaveric flamingo could not be stably held in a two-legged pose, suggesting a greater necessity for active muscle force to stabilize two-legged versus one-legged postures. First, we demonstrated that flamingo cadavers could passively support body weight on one leg without any muscle activity while adopting a stable, unchanging, joint posture resembling that seen in live flamingos. “Yet we can even see this behaviour in humans to some extent if they’re in a queue: people will rest more weight on one leg than the other.Flamingos (Phoenicopteridae) often stand and sleep on one leg for long periods, but it is unknown how much active muscle contractile force they use for the mechanical demands of standing on one leg: body weight support and maintaining balance. It just so happens that because flamingos have such long legs, we see it more,” says Rose. Ducks, geese, swans and flamingos are birds of a feather, using similar locking mechanisms in their legs to stay perfectly balanced. Interestingly, they aren’t the only animals to engage in this behaviour.