When you look up, the sky may seem calm and even but air is always on the move. Fluid flows like water, with eddies and currents, sometimes smooth and serene, sometimes tumultuous and violent. If an aircraft strikes it, the most turbulent air can cause injuries or even death, as well as structural damage to planes. According to a 2024 study, aircrafts encounter moderate to severe turbulence 68,000 times every year. Turbulence can cause uncomfortable bumps or throw an aircraft out of control, inducing chaotic rolls, pitches, and yaws. Although modern aircraft are equipped with sophisticated weather radar systems that pilots use to identify and navigate around areas of turbulence. However, some turbulence can be harder to spot. For example, the severe turbulence that struck the Singapore Airlines flight was caused by invisible "clear air turbulence" which can strike without warning, and is one of the biggest causes of weather-related aviation accidents. Clear air turbulence mostly occurs at high altitudes, where aircraft cruise in seemingly calm blue skies. It can't be seen by the naked eye and is undetectable by onboard sensors. Even satellites can't see this kind of turbulence. From 2018 to 2019, researchers at Swansea University flew an ultralight aircraft alongside a flock of homing pigeons. Using GPS, barometric pressure, and acceleration data loggers attached to the birds — over 88 flights — they measured the turbulence levels during the journeys the birds took to return to their lofts. They found birds migrate for thousands of miles — with wind speed, direction and turbulence all dictating the route they travel and the amount of energy they expend. Upon their findings, they suggested the possibility of using bird-borne sensors to shed light on air turbulence, much like the seal-borne sensors used to measure salinity and sea temperature. They concluded that birds could act as meteorological sensors on the move continuously collecting data about the turbulence they're experiencing along their flight paths. This would be cheaper than using sensors fitted to aircraft, plus birds can fly in conditions that planes can't. In another 2020 study, researchers followed the flight of Andean condors, the world's heaviest soaring birds. They documented when and how individuals gained altitude, and recorded each and every wingbeat. The data revealed the lowest levels of flapping flight recorded for any free-ranging bird, with the condors spending an incredible 99% of all flight time in glide-mode for more than five hours. This research provides insight into the way soaring birds exploit thermals, knowledge which could potentially feed into the programming of autonomous flying vehicles. (By Katherine Latham, BBC report)