by Michael Totten

Created on: November 04, 2008   Last Updated: November 18, 2008

As the cheetah is the fastest animal on land, so the peregrine falcon (Falco peregrinus) is the fastest bird in the skies. A member of the raptor family of birds, the peregrine hunts by flying for extended periods at very high altitudes while searching the ground and skies below for suitable prey. When it spots a quarry, it goes into a steep dive, controlled only by the tips of its wings. It is this stoop, clocked at upward of 200 miles an hour, which gives the peregrine falcon its reputation for speed.

The stoop itself is one of nature's most stunning achievements. With the help of modern timekeeping equipment and cameras capable of being fitted onto a small falcon without significantly impacting its performance, the exact dynamics of a peregrine falcon's flight can be seen as never before. We now know that the stoop is not a controlled straight fall but is actually a tight logarithmic spiral. This happens because the peregrine's eyes are set at an angle of about 40 degrees to either side, allowing it to scan a greater surface area for prey, but this also means it cannot best see its prey except at an angle. In order to keep the prey centered within the deep fovea of one of its eyes, the sharpest part of its vision, the stoop becomes a spiral with the prey caught in the middle.

In 2005, Ken Franklin recorded the fastest stoop time yet seen, a stunning 242 miles per hour, just short of the falcon's predicted terminal speed of 250 miles per hour at low altitudes. However, the peregrine is built so well for stooping that its wings are incapable of soaring.

There are unique anatomical problems to moving at such speed. Some are minimized by the behavior patterns of the peregrine falcon, while others are built into the body of the bird. The peregrine falcon minimizes air drag and potential damage to its wings by tucking in its feet and folding back its tail and the greater part of its wings just before it begins its stoop. The pale buff coloring of its underside makes it very difficult for potential prey to spot high against the pale sky, adding to the surprise of the attack, while the slate blue of its upper body blends well into the cliffs and rocky ledges on which it prefers to roost. The damaging rush of air through its lungs is mitigated by small bony tubercles in its nostrils. Its eyes are protected from dust and other debris in the air with a nicitating membrane, sometimes called a third eyelid, while the dark markings around its eyes help reduce glare and improve

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