Seeing is everything: Falcon eye surgery
A cataract can be seen in Banner’s left eye during a visit to Fisherville Animal Hospital and Bird Clinic in Penacook. Right: A peregrine falcon with clear eyes at the International Center for Birds of Prey in Awendaw, S.C.
** ADVANCE FOR SUNDAY APRIL 2 ** A peregrine falcon rests on the glove of Stephen Schabel, director of education, at the International Center for Birds of Prey, Friday, March 24, 2006, in Awendaw, S.C. The center opens its doors to the public for the first time later this year. (AP Photo/Mary Ann Chastain)
The mother of four baby peregrine falcons squawks on the George Washington Bridge, over the Hudson River, in New York, Tuesday, May 21, 2013. The chicks hatched three weeks ago on a girder six feet below the bridge's lower level. Their parents are among 20 pairs of peregrine falcons living in New York City. (AP Photo/Richard Drew)
Cataract surgery for humans is fairly routine and in the world of veterinary ophthalmology, the same surgery is often performed on dogs. Birds? Not so much. Dr. Ruth Marrion, a Massachusetts-based veterinarian, will perform the surgery Sept. 12 on Banner, a young Lanner falcon from the New Hampshire School of Falconry. Marrion has performed surgery on birds before, but for this operation, there is a groundbreaking twist: It’s the second time that veterinarians will attempt to implant an artificial lens into a raptor – and the first time for a falcon.
Vision is life
Raptors, including falcons, attack their prey by diving at high speeds from great distances. They keep their head aligned with their body for speed, but they also need maximum visual acuity to identify motion and prey in their peripheral field of vision as well as to judge speed and distance – both their own and that of their dinner.
Humans have round eyes, which allow us to look about without moving our heads. But a falcon’s eye is bell shaped and the sclera (the white of the eye) isn’t a fibrous tissue like ours. It’s bone. As a result, the falcon has to move its head if it wants to look in another direction. This sets up a dilemma: turn the head and become less aerodynamic or keep it aligned and miss what’s happening on either side. Fortunately for the falcon and other raptors, they have built-in equipment to handle the situation.
The retina is a layer of specialized cells in the back of the eye that receives light. The fovea is a super-specialized area of the retina that we need for reading and other tasks that demand fine vision. Birds have better visual acuity than people. Most birds (and people) have one fovea within their eye but birds of prey, like falcons, have two (bifoveal). A falcon can see up to eight times more detail than a human eye. The extra fovea extends peripheral vision to help them identify motion and to judge speed and distance. A falcon with cataracts can’t see well enough to hunt and couldn’t live in the wild.
The surgery done on Banner will be similar to surgery done on humans, but on a smaller scale. The lens, which is the same shape as a magnifying glass, has two parts: a thin covering called the capsule, which is like a baggie, and the contents, which are normally clear like a raw egg white. A lens with a cataract is like a baggie filled with cooked egg white.
Cataract surgery involves making a hole in the baggie and using an instrument with a long needle to enter the lens through the hole. The needle ultrasonically vibrates the contents and sucks them out, leaving an empty, clear baggie. In people, an artificial lens specifically made for an individual is implanted into the baggie, restoring normal vision.
Since the lens needed for the falcon’s eye is so small and not commercially available, Marrion has negotiated to have a lens made by a company that usually makes lenses for dogs. By implanting an intraocular lens into Banner, the surgery could restore the falcon’s vision to normal.
Different species of falcons are found all over the world, except Antarctica. There are more than 40 species, including six found in the United States. Lanner falcons are native to Africa and southeast Europe and parts of Asia. Here are some stats:
Size: About the size of an American crow, Lanners measure 17 to 20 inches long with a 40-inch wingspan and weigh about 2 pounds.
Life span in the wild: Up to 17 years.
Diet: Mostly small birds and occasionally rodents or other small animals.
How they hunt: Unlike the peregrine falcon, famous for diving at speeds of almost 200 mph, Lanners hunt horizontally, attacking low, flat and fast. Lanners are also one of the few raptor species known to hunt cooperatively. When a mated pair hunts together, the male generally flushes prey for the female to capture. Sometimes, both birds trade off pursuing prey across the sky. Small groups of Lanner falcons have been seen hunting in packs during lean winters.
Habitat: Arid, open terrain.
Ancient presence: Lanner falcons, with their wide eyes, are thought to be the species of bird depicted in the hieroglyphics in Egyptian tombs.
Endangered in Europe: Lanner falcon populations in their native Africa are thought to be increasing, but they are considered endangered in Europe. Their habitat there is decreasing, and Lanners will abandon nesting sites that have been disturbed by rock climbers or people stealing eggs to sell to collectors, zoos and tourists.
Falconry: Hunting wild prey with raptors may have had its origins in the steppes of Mongolia between 4000 and 6000 BC. By the 6th century and into the Middle Ages, falconry became a sport and surged in popularity throughout Europe. Known as the sport of royalty, possession of falcons and other birds of prey was a status symbol among the elite. During the reign of Edward III (1327-77) theft of a raptor was punishable by death. The decline of the aristocracy and the use of firearms diminished popularity for the sport by the 1800s. Today, it is estimated that 10,000 individuals legally practice falconry – about 5,000 of them in North America.
Sources: Nancy Cowan, New Hamsphire School of Falconry, Deering; Dr. Ruth Marrion, Bulger Veterinary Hospital, North Andover, Mass.; Vance A. Tucker, Duke University; hawk-conservancy.org; William Hodos, professor emeritus, University of Maryland; University of California Davis School of Veterinary Medicine; U.S. Fish and Wildlife Service; Cornell Lab of Orinthology (allaboutbirds.org); falcons.woodmen.org; animals.nationalgeographic.com; pbs.org; Falcon Research Group Southern Cross Peregrine Project; aviary.org. Graphics by Charlotte Thibault / Monitor staff.