Have you ever seen one bird chasing another through the air at breakneck speed, and wondered how it keeps from colliding with branches?

If you were careening through the forest that fast, you'd probably end up splattered against a tree!

One thing that helps birds avoid obstacles is their high "flicker fusion frequency." That's tricky to say, but easy to understand.

Suppose you flick a light on and off. As the rate it flickers gets faster and faster, eventually you don't see the light go on and off any more, but instead you see the light as a continuous beam. The rate at which you don't see the flicker anymore is called the flicker fusion frequency.

In bright light, humans have a flicker fusion rate of about sixty flashes per second, but in birds it's much higher, about one hundred per second. In fact, it may be even higher in birds like hawks, whose survival depends on speed and accuracy.

Flicker fusion rate affects how well you can see details while moving. Since birds have evolved to move at faster speeds than humans, a high flicker fusion frequency gives birds better visual acuity. When moving at high speeds, a bird can perceive and avoid obstacles in a fraction of the time that you could.

Human visual systems evolved to function best at walking and running speeds. However, when you get behind the wheel of a car, you move much faster, and unlike a bird, your visual system isn't optimized for speed, so your ability to see obstacles decreases as your speed increases.

Next time you're tempted to break the speed limit, remember the limits of your flicker fusion frequency, and slow down!