People: Monica Daley

Researchers investigated how running birds negotiate single-step obstacles. It is important that running animals control their legs to ensure that energy costs are minimised, to avoid injury, and achieve the preferred speed and direction. As these aims can often be conflicting, some tasks must be prioritised over others. The team wanted to know how the primary control priorities of body stability (maintaining the same body movements), energy saving, and leg safety, varied with different body sizes and terrain. 

The team predicted that, within complex terrain, control priorities may shift away from energy saving and toward the avoidance of falls and injuries - as the latter is more critical to survival. Priorities may also differ depending on body mass. The muscles and bones of larger animals are under greater stress so are at higher risk of injury; whereas for smaller animals the terrain is relatively rougher. We would, therefore, expect larger birds to prioritise injury avoidance and small birds to maintain body stability. 

  ostrich running in a laboratory     

During the experiment, ostrich, quail, pheasant, guinea fowl, and turkey, were presented with a visible single-step obstacle. The obstacle forced the birds to prioritise either body stability or energy saving and leg safety during locomotion. Quail and ostrich have a body mass differing five hundred fold, and the body mass of the other species lie between these two extremes. Thus, by comparing the response of these birds the team could determine which outcome was prioritised, and whether there was a shift in priorities with increasing body size.

The results show that energy saving and injury avoidance are important leg control priorities in running animals. Although body stability may result from these priorities it is not a direct objective. The team found that body size does not “substantially influence obstacle negotiation strategies.”

This improved understanding of animal control priorities may aid the production of more agile and energy efficient bipedal robots and prosthetics; as it demonstrates that robots do not need to be programmed with body stability as a specific priority.

The team included Dr Monica Daley and Dr Aleksandra Birn-Jeffery from the Royal Veterinary College. This research is published in the Journal of Experimental Biology.

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