Raptors

All birds are vertebrates and belong to the scientific class Aves. By definition, birds possess feathers, wings, beaks, and scales on their legs and feet. Members of the class Aves are also warm-blooded, air-breathing and lay terrestrial eggs. There are two orders of raptors under the larger class of Aves: Falconiformes and Strigiformes. Birds of prey belonging to the order Falconiformes have strong bills that are hooked at the tip and sharp on the edges. This functions to cut and tear flesh from prey animals. Also, Falconiform raptors have feet with sharp, curved talons, opposable hind toes, and very sharp vision. They are generally strong flyers and carnivores.

Worldwide, there are approximately 286 species in the order Falconiformes. The members are distributed among five taxonomic families. The family Sagittariidae has one species, the secretary bird (Sagittarius serpentarius). Secretary birds, with lengthy limbs and short toes, resemble cranes but are in fact raptors. The family Pandionidae also has only one species, the osprey (Pandion haliaetus). Ospreys are fish-eating raptors that have unique foot structures. An adaptive characteristic for catching fish, one front toe of the osprey can swivel backward to join the back toe. Accipitridae is the largest family containing 217 species. Bald eagles (Haliaeetus leucocephalus), red-tailed hawks (Buteo jamaicensis), buzzards, and some vultures belong to this family. Vultures are large black raptors with very long wings. A stereotypical behavior of vultures is high, circular soaring in groups. Their large wingspans are adaptive for soaring, which takes advantage of thermal air currents. Their diet consists mostly of carrion, which they spot or smell from the air.

The family Cathartidae, the New World vultures, includes the turkey vulture (Cathartes aura) of North America. Members of this family of raptors feed primarily on carrion. Their largely unfeathered heads attached to long necks allows these birds to immerse their entire head inside of the bodies of dead animals while feeding. A characteristic that distinguishes them from Old World vultures is the presence of a perforated nostril, which creates a large hole in their beaks thought to facilitate their sense of smell.

The family Falconidae contains falcons. Falcons are a particular group of hawks belonging to the same genus. They are made distinct by their large dark eyes and notched beak. Typically, falcons have long pointed wings and tails. Unlike other hawks, however, they do not build nests from sticks. Rather, falcons carve spots on cliffs or nest in natural depressions. Falcons are famous for their acrobatic flight, and are sometimes kept by falconers as pets. Two well-known falcons of the United States are the American kestrel and the peregrine falcon.

The phylogenetic order Strigiformes consists of owls. Owls are nocturnal predators with powerful beaks and feet, talons, large eyes capable of enhanced night vision, extremely sensitive hearing, and special feathers that create noiseless flight. The silent flight that owls exhibit allows them to stealthily catch prey without startling them, preventing escape. Although hawks and owls belong to separate orders, they share the common trait of being predatory and catching food with their feet. Some owls have tufts on the tops of their head, often called horns or ears, as in great honed owls. In reality, these tufts are feathers. Owl ears are located underneath feathers on the sides of their heads and are not visible. Tufts likely serve behavioral signals to other owls, or as camouflage. Like hawks, owls can be found living in the same areas year-round. There are approximately 135 owl species worldwide.

Raptors display a wide range of sizes. One of the smallest birds of prey is the pygmy falcon (Polihierax semitorquatus) which lives in Africa. This species weights only about 60 g (2.1 oz.) and has a wingspan of about 1 ft (0.3 m). The smallest North American raptor is the American kestrel. American kestrels weigh about 4 oz (120 g). and have a wingspan of about 1 ft (0.2 m). The largest diurnal bird of prey is the Andean condor, which can weigh up to 31 lb (14 kg) and has a wingspan of up to 9 ft (3 m). The largest raptor in North America is the California condor, having an average wingspan of up to 9 ft (3 m).

Some species of raptors display sexual dimorphism. Species of animals showing sexual dimorphism have males and females that possess distinctly different physical characteristics. For example, some raptor species have females that are much larger in size than males. Others vary in coloration between males and females. Most birds of prey that are diurnal have feather color patterns that are earth tones: brown, black, gray, white. However, feather patterns themselves may be distinct, as in the bald eagle or peregrine falcon. In contrast, the skin of the heads and necks of some vultures and buzzards can be very boldly colored in red or orange. The shape of raptor wings can foretell its foraging behavior. Most hawks and eagles have wide, rounded wing margins that function in soaring upon air currents. Wide wings do not provide great speed compared to other wing shapes. Instead, hawks rely on surprise to catch prey. A few hawks, however, have short wings for bursts of speed and maneuvering in wooded areas. Falcons, in contrast, have sharp angular wings that allow these raptors to fast chase and make steep dives to catch their prey.

Raptor beaks are very strong. Beaks are composed of bone covered with plates of keratin, the tough protein found in human fingernails. Raptor beaks are sharply hooked at the tip and are sharp along their edges. Some species have beaks that reflect their feeding habits. For example, falcons have notched beaks that are used to break prey vertebrae. An equally important characteristic of raptors is their excellent vision. Vision is the most important raptor sense in hunting. When compared to many other vertebrates, raptor eyes are much larger. Their size allows for sharper images and greater sensitivity to light and color. Like humans, raptors have binocular vision. That is, they use both eyes to perceive images. It is estimated that raptors can see up to three times better than human beings.

Diurnal birds of prey can be found in almost any habitat, including such inhospitable biomes as deserts and tundra. Representatives of the Falconidae, Accipitridae, and Pandionidae are found on every continent except Antarctica. Other species have very localized distributions. For example, the secretary bird is restricted to sub-Saharan Africa only. New World vultures exist only in the Western Hemisphere, while Old World vultures are found exclusively in the Eastern Hemisphere.