Birds can sleep upright thanks to tensegrity, an architectural concept based on the balance between tension and compression. Their legs act as self-supporting columns held in place by tendons and muscles. The light yet resistant bone structure, combined with this anatomical arrangement, creates a stable support system. During sleep, birds lock their knees into position, keeping the structure in balance without constant muscular effort. This ingenious adaptation enables them to rest while remaining alert to react quickly in the event of danger.