Birds run carefully in the rough.
Placing feet in the right place concerns robots and runners, and almost all bipeds and tetrapods. Here is an article of interest to in Runners. The UKs Royal Veterinary College (and Oregon State University) have often studied small crouching creatures and large upright birds such as ostrich. The mass of these birds ranges from 0.2kg to 117kg, so the strategy for movement could be extremely varied.
Aleksandra Birn-Jeffrey, Monica Daley and 4 colleagues published their findings in the science journal JEB as Don't break a leg: running birds from quail to ostrich prioritise leg safety and economy on uneven terrain. Being bipedal, stability of the body seemed likely to be a priority, but the maintenance of consistent forces from the running legs was found to be more important. Economy in terms of energy expended and the safety of the legs turned out to be major results of that consistent running mode, no matter how uneven the ground was.
When birds first flew, it would have given them ecological advantages. If take-off speed was a precursor, however, then running in a stable manner could have influenced avian evolution too. The stability of the animal does seem to be a control priority for many species. As all birds are dynamically similar as they approach a step obstacle (from 0.1 to 0.5 times their leg length), the leap they make onto the object seems to be followed by a crouch that keeps them stable there. The forces exerted in the procedure showed up how they negotiated the steps. They all jump off with extended legs.
Some ostriches used in the experimental work had to be reared from chicks for 2 years, so that their imprinting on humans could be used to decrease any aggression and enable handling. These big guys were expected to vault upward and then immediately step down, but every bird performed the basic crouch on top of the step.
With an Oregon University computer model, the runners could be modelled exactly. They discovered 2 alternative “task level priorities.” The prioritisation off stability and returning to the steady gait required for running was one. The other involved minimising the costs to the bird in energy exertion. The model simulated the cautious responses of all of the birds if the leg posture was carefully controlled to avoid the leg being overloaded.
Next, a very stable, bipedal robotic ostrich which we will all find very useful for ---?
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