A Bird’s-Eye View

Joe Meche is president of the North Cascades Audubon Society and also serves the chapter as newsletter editor and Birding Programs Coordinator. He has been watching birds for over 50 years and  photographing birds and landscapes for more than 30 years.

The term itself applies to the view of an object or larger area from above. It’s often used in making blueprints, floor plans, maps, and for an assortment of other applications. Bird’s-eye views have been used since classical times and to some, it’s considered to be another form of envy that humans have for birds. They have the ability to soar above everything and take in a broader view than we’re allowed in our earthbound state. Score another point for the birds!

Birds are visual animals and while they spend their days and nights in search of food, they are always on full alert for predators. The working parts of avian eyes are similar in many respects to those of humans, but have evolved in a variety of ways to accommodate the particular needs of a range of species. Birds have the largest eyes of all vertebrates in proportion to their body size and, along with humans, rely more on their eyes than any other sensory organs.

Through the process of adaptive evolution, human forebears remained in the trees and on the ground in search of food while the ancestors of contemporary birds left the treetops and soared above the landscape. Their eyesight evolved as a means for them to better observe the world below and the sky above as they searched for sustenance. It is generally understood that humans and birds developed a better sense of sight to compensate for their poor sense of smell.

Part of an old adage supposes that one of the three characteristics of the perfect animal would be the “eyes of an eagle.” The visual acuity of birds is significant, and people with really good eyesight are often referred to as being “eagle-eyed” or given the nickname “Hawkeye.” Traditionally, we have ascribed extraordinarily keen eyesight to birds. Although this is true to some extent, it’s not quite to the extreme that we’ve come to believe.

Perching birds and raptors have the sharpest eyesight of all birds, and they can make out details at anywhere from two and one half to three times the distance that humans can. Some raptors can see prey in detail from as far as a mile away. In addition to their superior vision, birds also have the ability to see the whole picture as opposed to having to scan in the manner of humans.

Since the eyes of most birds are set on the sides of their heads and fixed in their sockets, they see more by turning their heads and necks. They also see better to the side than to the front, resulting in monocular vision. For smaller birds that are often prey species, such as shorebirds, their vision is wider ranging and extremely helpful in keeping a watchful eye out for predators like falcons and hawks.

Avian eyes also have a limited range of rotation and they rotate primarily toward the tip of the bill. Because of this limitation, birds are constantly moving their heads back and forth and up and down to see the whole picture. As the sight lines of each eye overlap to the front, binocular vision is enhanced. Depending on the species, binocular vision comes into play sooner because of the position of the eyes on the head.

Binocular vision in raptors has evolved due to their speed and the constant need for determining distances to prey that is often in motion as well. This is most advanced in owls and because of the placement of their eyes, their overlapping vision is as good as that of humans.

The extraordinary eyesight of owls is due primarily to the shape of their eyes, which are very long, as opposed to the spherical shape of the human eye. The elongated eye shape gives owls greater telescopic vision, which enables them to see small shapes from great distances. Other adaptations let a maximum amount light into the eye, allowing them to hunt in dim light. With superior night vision and superb hearing, owls are formidable nocturnal predators.

One of the oldest myths about birds is that owls can turn their heads completely around a full 360 degrees. This myth comes up about 90 degrees short of being true. The fact is that owls are capable of rotating their heads approximately 270 degrees. If an owl follows an object that is circling its position — such as a tenacious photographer — it swings its head around so quickly that it appears to have turned its head completely around, thereby perpetuating the myth.

The area that birds can see when holding their heads perfectly still varies among the different species. Pigeons are perhaps at the head of the class in this department. With their eyes set on the sides of their heads they can boast a total view of about 340 degrees. Their ability to see straight ahead covers about 24 degrees of that total with their binocular vision, and the only place they cannot see is directly behind their heads.

Similar parts of avian and human eyes are the cornea, retina, sclerotic ring, lens and optic nerve. To scientists, perhaps the most intriguing part of the avian eye is the pecten, an elaborate pleated structure that is attached to the retina near the optic nerve. Numerous theories have attempted to explain the function of the pecten. Most of the theories contend that the pecten functions as a source of nutrition and oxygen for the retina, which has no blood vessels.

Birds have upper and lower eyelids, which are folds of skin above and below the eye. Diurnal birds tend to close their eyes by drawing up the lower lid while the upper lid is more active in nocturnal birds. A third eyelid, the nictitating membrane, can be drawn across the eyes, upward and to the rear to moisten the cornea.

Like humans, birds possess excellent color vision, which plays an important role in their often complex and colorful courtship displays. Given the amazing array of colors that birds exhibit during their respective breeding seasons, imagine them not being able to differentiate between colors. Would the color be necessary if they had no color vision? Would all warblers be black and white?

Avian eyes are truly one of the marvels of nature. Birds gather more information through their eyes than through all their other sensory organs combined. A true bird’s-eye view must indeed be something to behold. §

The perfect animal would have the eyes of an eagle,
the ears of a deer, and the nose of a grizzly bear.

— Anonymous