Swifts are Silvers who can move at an extraordinary physical speed. They are known to make excellent spies.
"Swifts are perceptors, with enhanced speed and endurance. Trained and talented swifts can move almost faster than human perception. They are much faster than silks, and before the advent of radio communication were used as speedy messengers throughout many Silver kingdoms. Swifts often form advance troop regiments. Like silks and shadows, they make for adept spies." -Victoria Aveyard "War Storm" "On Silverblooded Abilities"