Why birds speed up to slow down: The physics of landing

Birds often flap their wings as they approach a landing, even though powered flight consumes more energy than gliding. Experts at The University of Manchester utilized mathematical modeling to elucidate the reason behind this behavior. According to the study published in Proceedings of the Royal Society A Mathematical Physical and Engineering Science, a bird flying without flapping its wings would theoretically be able to reach zero speed precisely at the moment of touchdown.

However, such a maneuver would necessitate significantly higher approach speeds and a much larger horizontal distance, around 60 meters (197 feet), and a vertical climb of about 20 meters (66 feet). These findings imply that achieving the lowest possible touchdown speed may not always be feasible. Flapping wings may not solely serve the purpose of slowing down but also allows birds to accomplish the touchdown within the limited spatial constraints of a real landing situation.

The study also sheds light on why some birds swoop while landing on a perch and how the physical demands of landing may have influenced bird evolution. Dr. Ben Parslew, the lead author and lecturer in aerospace engineering at The University of Manchester, stated that while landing appears effortless, it poses a fundamental physical challenge.

Slower flight leads to reduced aerodynamic control, thus requiring birds to devise a method to decrease their speed while maintaining safe maneuverability. The researchers employed mathematical modeling to determine how a bird could minimize its speed upon touchdown without flapping, while still retaining the necessary control to execute the maneuver.

This research not only provides insight into the swooping approach observed in certain perching birds, such as raptors, but also aids in comprehending how the physical demands of landing may have contributed to the evolution of birds.