Bats are a common source of inspiration for roboticists. For the elegance of their wingspan and their effective use of sonar to get around, they’ve even been called the “holy grail of aerial robotics.” Most recently, researchers have also shown how looking to bats may help engineers develop drones that are significantly more energy efficient.

The secret is mimicking how the winged animals can take a load off pretty much anywhere they want. This is according to Kaiyu Hang, a postdoctoral associate at Yale University, and the inventor of a new kind of retrofitted quadcopter that uses its own pair of legs to roost. Hang tells Inverse it could offer a way to help develop drones that are far more impervious to issues around battery life.

See also: Researchers Develop a Remarkable Flying “Bat Bot”

So how can we teach drones to take rest-stops with the efficient effortlessness of a bat? Hang’s drone uses three long gripper fingers, which kind of resembles a hawk’s talon, to allow the new drones to “perch” and “rest” on ledges, poles, and scaffoldings.

Perching is an existing technique that allows a given drone to land on an object and power down while continuing to record video, say, or waiting to receive a package.

Hang tells Inverse that this new version of resting takes that concept a step further by allowing the drone to partially shut off sooner and for longer, enough to conserve between 40 and 70 percent of its energy. These bat-like drones, as you can see in the video below, do not require a flat, even surface on which to land.

Hang's drone uses its claw-like landing gear to "perch" like a bat. Hang et al., Sci. Robot. 4, eaau6637 (2019)

“Resting has not been investigated before and this is the first time being proposed,” he explains. “Comparing to perching, this new capability has enabled the unmanned autonomous vehicle to make use of a much larger range of common structures in the environment, and made it possible for it to more flexibly interact with the environment to achieve many more different tasks.”

It’s a (deceptively) small seeming tweak that could make a huge difference. Drone battery life, which lasts roughly 30 minutes tops, is one of the main limitations standing in the way of drones that can engage in more exciting use cases, from better helper drones in industries like construction, to drones that can engage in search and rescue. Hang’s experimental drone has already showed great promise for pulling off these kinds of tasks, and his findings were published in the journal Science Robotics Wednesday.

In the study, Hang shows how his aircraft was able to hook itself to a clothesline-like pole and hang upside down like a bat. It was also able to make use of various types of specialized feet that let it lean on building corners and prop itself up on poles. It’s a big leap toward drones that are much more suited to long-term use in urban settings.

Examples of various perching and resting actions. Credit: Hang et al., Sci. Robot. 4, eaau6637 (2019)

Pulling off these maneuvers in the real world won’t only improve flight time, but Hang said it could also improve safety, making delivery drones more commercially viable.

“While resting at the edge of a windowsill, a drone will be able to deliver objects to someone inside, without the need of keeping the rotors at the window side still working,” he said. “So as to reduce the risk for humans to interact with it.”

There’s still work to be done before Hang’s experiment makes it into the real-world. As it stands, the drone in the experiment still relies in part on human assistance to rest.

The next version of these bio-inspired drones will need to have the capability to scan the area around them with an on-board sensor to find these resting opportunities on their own. But Hang says he thinks this should be relatively simple to pull off (the sensor used in his experiment was hardly cutting-edge: an Xbox One Kinect sensor.)

Drone perching on a ledge. Hang et al., Sci. Robot. 4, eaau6637 (2019)

Drones with resting capabilities would also need to account for wind and other physical disturbances that could cause them to crash. But that could be accounted for by creating a joint between the drone and its legs that soaks up the any brisk motion that could damage the landing gear or the drone. Hang plans to begin working on this next component later this year.

“We plan to design a tilt-pan connector between the main body of the UAV and the modular landing gear,” he explained. “By mechanically decoupling the movement of the drone’s main body from the landing gear or by actively compensating the disturbances at the connector the pose stability can be further improved.”

If he’s able to showcase an example of a drone being able to land on its own and deal with gusts of wind, then drone based deliveries no longer will seem like all that much of a stretch.

Other animal-inspired research is also helping pave the way for delivery drones, including efforts to develop drones that can flock like birds. This, researchers think, may offer the key to preventing the delivery bots of the future from colliding over our heads. Hang’s research is yet another example of avian-inspired robots could soon become an important part of everyday life.