There are two different ways to measure flight speed: level flight, meaning the speed it takes to fly in a straight line, and diving flight, meaning the speed at which the bird plunges down to kill its prey. The latter type of flight is generally much faster, but for obvious reasons, it can only be sustained for a few seconds at a time.
Complicating matters is that many species are classified according to the highest recorded individual flight speed rather than the average flight speed. This video will take all factors into account when listing the fastest birds in the world.
