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Raptor is a term currently used by many to describe birds of prey. Unfortunately, there is some confusion, since many birds regularly feed on animal prey. Robins feed on worms, woodpeckers on grubs, herons on frogs, etc. However, most people think of eagles, hawks, falcons, owls, and even vultures, as raptors, or birds of prey. Three specific anatomical features qualify these as raptors: strong grasping feet equipped with sharp talons, a hooked upper beak, and excellent binocular vision.   Worldwide, there are 320 species of hawks, falcons, vultures, and eagles (order Falconiformes) (33 in North America) and 200 species of owls (order Strigiformes) (18 in North America). In northeast Indiana, there are 8 regularly breeding species of Falconiformes and 3 breeding species of owls. Another 5 hawks, 2 eagles, and 4 owls join these during migration and winter visits.   A raptor is designed both behaviorally and physically to promote survival. First, raptors are an exception in the bird world when it comes to egg laying and incubation. Most birds will lay a complete clutch of eggs before incubation starts. Raptors, however, start incubation as soon as the first egg is laid. Thus the eggs will hatch on succeeding days, giving the first hatched the best chance of receiving food. If there is abundant food, then the remaining nestlings will receive a fair share; otherwise, only the first hatched will have the best chance at survival.   Second, specialized adaptations, such as specifically adapted feet and beaks, highly developed vision and hearing, and exceptional flight capabilities, help raptors find and capture prey. Additionally, raptors are designed to quickly and efficiently process their diets.   Feet are the primary weapons of death, and protection, for raptors. Their quite large and powerful feet can exert enough pressure to puncture thick skin, often crushing and killing prey instantly. Once a raptor catches something, the bird generally will not release it until the prey stops moving. The talon on the back toe is long, at least a full inch on eagles. An adult Golden Eagle exerts almost 200 pounds per square inch. The size of a raptors foot varies with the size of its prey: rodent hunters generally have short, stout toes, while bird hunters have long, thin toes to increase their grasping area. The spread of a Golden Eagles feet is about 9 inches.   Owls differ from most other raptors in that their feet are feathered down to the toes (some cold climate hawks also have this adaptation). Owls have two toes facing forward and two facing back, while most birds have three toes forward and one back. This configuration gives owls a better grip and a wider spread. This wider spread is especially useful for catching prey hidden below grasses or leaves.   Raptors have powerful hooked upper beaks, which are used primarily for tearing prey rather than for killing. The large beaks of eagles enable them to feed on large prey without immersing their heads in the carcass. This helps to keep the feathers clean and reduces the spread of bacteria. While most raptors kill with their feet, falcons use their beaks for both killing and protection. Falcons are the only raptors that have a tooth-like projection that is used for severing the cervical vertebrae of prey.   An owls beak is very similar to the beak of a hawk. However, the feathers that surround the beaks of owls are quite different from hawks. Short bristle-like feathers around the beaks of owls (which are far-sighted) help locate prey close to their faces in the darkness.   Raptors as a group, and particularly eagles, possess the best long-range vision on this planet. It is estimated that a raptors vision is at least eight times better than humans (what we can see at 20 feet, a raptor can see at 160 feet)! This amazing visual power is accomplished by the high density (8 times that of humans) of cells in the fovea, the most sensitive part of the eye. In fact, raptors have two fovea, which allows triangulation of targets.   Unlike most birds, raptors eyes face forward, providing binocular vision.   A raptors eyes are large and permanently fixed in the skull. To shift their gaze, they must move their heads from side to side and even directly backward. They possess long flexible necks and can turn their heads up to 270 degrees and some even upside down!   The eyes occupy most of the space in the skull. A Great Horned Owl, which weighs only 2 pounds, has eyes the size of humans. They are tubular, rather than round, which allows better focusing. If humans had eyes proportional to the eyes of an owl, they would be as big as softballs and weigh 5 pounds!   All raptors have a third eyelid called a nictitating membrane. At the instant a raptors feet touch its prey, this membrane covers the eye, protecting it from possible damage by a thrashing victim.   The eyes of owls are at least 35 to as much as 100 times more sensitive to dim light as the eyes of humans. Roughly, this means that an owl can see everything perfectly at a distance of 1200 feet illuminated by a single candle!   The increased sensitivity to light produced by the large concentration of rods has limited the number of color sensitive cones. Because of their limited ability to see color, especially at night, birds such as owls have no need for bright feathering; thus these raptors have a very limited range of plumage hues. Owls rely on voice and body posture for display, rather than the flashy color patterns displayed by most breeding birds.   Hearing is very highly developed in raptors. The wide variety of noises made by raptors indicates that their hearing is both broad ranged and acute. In addition to communication, raptors use hearing as a means of locating food.   Owls can hear sounds 10 times fainter than humans can detect. Large ear openings, surrounded by deep soft feathers, funnel the sounds to each ear. The facial feathers are arranged like parabolic dishes, which focus the sounds into the ears.   Owl ear openings may be of different shapes, or placed asymmetrically on the head. These differences allow the owl to distinguish slight variations in sound arrival time and volume, thus precisely locating the origin of sounds both in the vertical and horizontal planes. By slowly moving its head, the owl can directly face its prey.   Flight is the utmost evolutionary accomplishment of birds. To facilitate flight, birds have developed feathers, light weight skeletons, a reduced streamlined digestive system, and a supplemental breathing system, to mention a few.   Nothing can equal a feather for warmth, strength, and lightweight. Most raptor feathers are similar in type and function to other birds. Some adaptations include long flight feathers for the soaring hawks. Long stiff flight feathers produce noise as they move through the air, which would be detrimental to the owls that depend on their hearing to locate prey. Owls, therefore, have soft flexible feathers and, thus, an almost silent flight. An owls primary feathers have a serrated front edge, which breaks up the flow of air and deadens the sound of wind rushing across the wing. Additionally, owls have large broad wings, which enables slow gliding flight.   Hawks, which must see their prey, need to hunt over larger areas. Many hawks (genus Buteo), eagles, and vultures depend upon long broad wings and tails to facilitate almost effortless soaring. These birds depend on thermals (columns of rising hot air) and air currents to support their flight. For additional lift and fine flight adjustments (trim), the individual primaries are separated at the wingtips to make slots that act as winglets.   In contrast to the slow soaring flight of vultures, eagles, and buteos, falcons and accipiters have adapted a different flight strategy. Falcons use high speed to deliver bone breaking midair blows to kill prey. A falcons compact feathers, long narrow pointed wings with stiff quills, short necks, strong shoulders, and large pectoral muscles are all specially adapted for speed. Accipiters, or forest hawks, have short rounded wings and long tails, providing the quick acceleration and maneuverability needed when chasing prey birds, especially through stands of trees. Harriers are raptors that seem to fit into several categories. With long narrow wings and tails, they fly low and slowly with upswept wings while hunting. Additionally, they possess facial disks like owls to focus sound to their ears.   Birds have a specialized digestive system that gets food quickly into the bloodstream. Raptors, like most hunters, never know when their next meal will be; they must be well adapted to feast and famine. In their esophagus is a crop, an enlarged area that allows for the ingestion of large amounts of food. With a full crop, a raptor can survive five to seven days without eating.   Raptors usually swallow their prey whole. To minimize digestive energy, items such as fur, feathers, and bones are fashioned into a pellet and coughed up. When the pellet comes up, the bones are wrapped inside the fur or feathers. This behavior is not only efficient, but appears necessary for good health.   Vultures demonstrate a different digestive and feeding system than the other raptors. Because they lack sharp talons and cannot kill their own prey, vultures live on a diet of rotting, and often diseased, carrion. By quickly disposing of infected carcasses, vultures help to reduce the spread of diseases. Their highly acidic digestive system kills many viruses and virulent strains of bacteria. Vultures possess other unique adaptations that destroy bacteria. Their bare featherless head stays clean while reaching into carcasses, and when this feather-free head is exposed to the ultraviolet rays of sunshine, bacteria is destroyed. Also, vultures defecate onto their own legs; again, the high acidity of their feces sterilizes the carrion-covered legs. Recent DNA results indicate that New World Vultures taxonomically belong in a subfamily of Storks. Rumor has it that the next AOU listing publication will, in fact, officially remove them from Falconiformes, and place these "odd ball raptors" under the family of Ciconiidae (Storks and New World Vultures).   Bird skeletons are lightweight yet strong. Heavy items such as jaws and teeth have been replaced and in some cases individual bones have been fused to form one. The bones are filled with air spaces (pneumatized) forming a "honey combed" interior. The bones of a bird weigh up to 30% less than the bones of a comparable mammal. Females store calcium in the hollow air spaces of several different bones, which produces a secondary bone structure called medullary bones. Later, the females use the calcium for producing eggshells.   The respiratory system of a bird has numerous air sacs in addition to lungs. These air sacs are used to store, moisten and sometimes filter the air that is breathed. The humerus bone of the wing is one of the bones used for ventilation storage. Falcons have special adaptations in their nasal passages to reduce air pressure during stoops.