The peregrine falcon is the fastest animal alive. These species evolved to snatch prey out of mid-air. In order to hunt in this manner, falcons need to be able to function in a world moving much faster than our own. A peregrine’s brain evolved to process images at a higher speed than human brains.
Human brains evolved to comprehend anything above 60Hz (or flashes of light) per second as a solid stream of light. This rate is called the Flicker Fusion Frequency (FFF), which is the frequency at which a flashing light is no longer detected as individual flashes and is perceived as one continuous stream of light. Most of the artificial lights around us are not solid light, they are flickering so fast that we perceive them as solid light. Human vision has an FFF of 60Hz, which works best with our walking and running speeds. When humans move faster than these speeds the world appears blurrier. When driving in a car at higher speeds, for example, our ability to see obstacles decreases.
Raptors, such as the peregrine falcon, are birds of prey. They developed a faster FFF in order to avoid obstacles and have a faster reaction time while hunting. Raptors can process much more visual information than humans, as their FFF is higher than 100 Hertz per second. They are living in a much faster world than our own. A peregrine falcon, diving at speeds faster than 180 miles per hour, can see its prey in enough detail to strike mid-air. This capacity to see the world in great detail is what allows raptors to be great hunters.
You have likely observed raptors perched on trees or telephone poles, staring out into a distant field, and wondered what they could be looking at. It’s likely they are watching something that you do not see.
Raptors are able to spot prey over one mile away. Their visual sensory cells, rods (perceive luminance) and cones (perceive color), are more tightly packed. Humans have roughly 30,000 cones in our fovea, the part of the eye responsible for our sharpest vision, used for reading, watching television, and other activities where we need to see details. Raptors have around one million cones in their fovea. Also, falcons and other raptors have two foveae in each eye (humans have one in each eye). This allows a substantial part of their field of vision to be processed through the most visually clear part of the retina, creating a much more detailed image.
Having two foveae allows them to focus on more objects at a time. The shallow fovea is forward looking focused. It provides binocular vision, allowing falcons to see objects far away and judge distances. The second fovea, the deep fovea, is lateral-looking. It provides visual information about close objects on their sides. This is like seeing the world through both a macro and zoom lens simultaneously. One fovea focusing on fine details right in front of you and the other looking at object further away.
Not only can falcons see things more clearly than humans, they also see colors beyond our spectrum. Falcons can see ultraviolet light (UV). Humans have three types of cones in our eyes (which allow us to see colors) red, green, and blue. Falcons have four types of cones, red, green, blue and UV. Seeing UV light is not unique to raptors, as a lot of bird species are able to see within the UV spectrum. This allows colors to stand out even more, giving a color boost to the plumage patterns of birds and other colors in their environment. It’s believed that seeing UV light may help improve their ability to identify shapes and textures. Most impressively, it is yet another function among the world of birds that humans are not privy to. It’s easy to see how a falcon’s view of the world would be much different from our own perspective.