Grounded Running in Birds: An Energy-Saving Strategy

A team of biologists and animal movement experts from the Netherlands and the U.K. has discovered that birds like the emu employ a grounded running technique at medium speeds. This approach helps them save energy compared to the ungrounded running method used by other animals, including humans.

Their research, published in Science Advances, involved creating simulations to analyze the emu's running style in greater detail.

When an emu runs at a moderate pace, it never leaves the ground entirely; one foot is always in contact with the surface. The team found that this grounded running style is more energy-efficient than the typical running technique, which involves jumping with each stride, particularly at medium speeds.

The study aimed to understand why birds have developed this particular running method while most other bipedal creatures tend to adopt an ungrounded style regardless of their speed.

To simulate the emu’s running, the researchers built a digital marionette made of muscle, bone, and tendons, with adjustable tendon stiffness to replicate different running styles. They initially taught the model to walk, followed by running.

When encouraged to minimize energy expenditure, the model naturally adopted a medium-speed grounded running style, closely mirroring the actual movement of emus.

The team also noted that the anatomy of emus, which has adapted to support crouching, restricts their ability to fully extend their legs. This anatomical feature likely influences their running style, as switching to an ungrounded method at intermediate speeds would require greater energy. The researchers propose that this running style may have originated with non-avian dinosaurs, which share similar anatomical traits.