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April 28, 2010--Hawk Vision

by Bob Sallinger

kgw.com

Posted on April 28, 2010 at 8:01 PM

Updated Wednesday, Oct 30 at 5:36 AM

The chicks are now about 14 days old and nearly one third of the way to their first flights.

 As you watch Raptorcam notice how both the parents and the young hawks frequently move their heads about to observe the world around them. Hawk eyes are much larger relative to their head size than human eyes . If your eyes were as large as the red-tails relative to your skull, they would be approximately the size of tennis balls. However, hawk eyes are also relatively fixed in their sockets--whereas we can simply reposition our eyeball to view the world around us, a hawk must move its entire head.

PHOTOS: Adult Hawks watch over chicks, 4/28

Nobody knows exactly how much better hawks are able to see than humans but different papers have put their visual acuity at 3-8 times that of humans. Red-tails have binocular vision to allow them to accurately track and swoop in on moving prey at high speeds. Many prey species such as songbirds and waterfowl have their eyes set more on the side of their heads to allow them to better scan in more directions for potential predators.

The red-tails have a bony ridge or shelf above their eyes. This ridge may serve to both protect the eyes and to reduce glare from overhead sunshine. Hawks also have a third eyelid known as a nictitating membrane. This eyelid is transparent and moves horizontally across the eye. It works almost like a windshield wiper cleaning and moistening the eyeball while also allowing the hawk to continue to see while it is moving across the eye.

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