If a Tyrannosaurus Rex living 66 million years ago featured a similar leg structure as an ostrich running in the savanna today, then we can assume bird legs stood the test of time – a good example of evolutionary selection. Graceful, elegant, powerful – flightless birds like the ostrich are a mechanical wonder. Ostriches, some of which weigh over 100kg, run through the savanna at up to 55km/h. The ostrich's outstanding locomotor performance is thought to be enabled by the animal's leg structure. Unlike humans, birds fold their feet back when pulling their legs up towards their bodies.

A team of scientists has constructed a robot leg that, like its natural model, is very energy efficient. BirdBot benefits from a foot-leg coupling through a network of muscles and tendons that extends across multiple joints. In this way, BirdBot needs fewer motors than previous legged robots and could, theoretically, scale to large size.