It’s a bird, it’s a plane … it’s a robo-puffin?

Given that water is 1,000 times denser than air, moving through those two mediums requires very different mechanics—or so one might assume. Yet birds like gulls and puffins can plunge into the sea, swim underwater, and leap back into the air to fly away. And now engineers at MIT and EPFL in Lausanne, Switzerland, have designed a robot that can do likewise.

The “flapping-wing aerial-aquatic vehicle,” or FAAV, weighs less than 300 grams (about half a pound) and is equipped with a central fuselage, two flexible wings, and a steerable tail. The body contains a battery and a waterproof electric motor that drives a crankshaft, which pumps the wings up and down at preset frequencies. The wings are made of thin membranes that are coated with hydrophobic nanoparticles to help wick away water. And the tail is motorized, enabling it to change its angle to help the robot fly up or dive down.

In experiments carried out in a water …