Owls are also highly evolved hunters and killers. They have the best hearing in the bird world — some owls, like the great gray, can hear a mouse moving under a foot of snow or more and swoop down and capture it without ever seeing it. In owls with a facial disc, the ears are hidden behind it, and are asymmetrical — one is higher than the other. That allows the birds to locate prey both horizontally and vertically for more accurate detection. The round face functions as a kind of satellite dish, funneling the sound to the ears, so the owl can make in-flight course corrections based solely on sound.
Their exquisite hearing does not mean that their powers of sight are diminished. Owls have many more rods in their eyes than humans, which bring in much more light, akin to natural night-vision goggles. Like humans, owls have binocular vision, which means they see in three dimensions. They can also rotate their heads 270 degrees. “In two turns,” Mr. Holt said, “they can see all around them.”
Their wings stand out as a marvel of evolutionary engineering. There is a comblike serrated feather on the leading edge of the wing, velourlike feathers on top and a trailing edge of feathers on the rear of the wing. “These three things combine to reduce aerodynamic flight noise,” so they can surprise their prey, Mr. Holt said. Being rigged for silent flying means they can also hear their prey better.
The owl also has the lowest wing-loading ratio of any bird, which means the wings are much larger than its body mass and provide a great deal of loft. “That gives them great aerial agility,” Mr. Holt said. “They can fly really slow, just above stalling speed. It also gives them the ability to gain lift easily with prey.”