Raptors

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Raptors

Raptors, or birds of prey, are birds having the following three distinctive characteristics: strong grasping feet equipped with sharp talons, a hooked upper beak, and keen vision. Raptors are called birds of prey because these features allow them to be predators that hunt for their food. Many raptors are, in fact, predators. Some raptors actually hunt for and consume other birds. Other members of the group, however, eat only dead animals, called carrion. Raptors consist of two taxonomic orders of birds. The order Falconiformes comprises falcons, hawks, eagles, vultures, condors, and related birds of prey. Falconiformes birds are diurnal (daytime) predators. The order Strigiformes is composed of owls. Owls are also birds of prey. They are, however, nocturnal predators that are adapted to hunt primarily at night. Spectacular hunters, raptors are admired for their majestic strength. For example, eagles have often been used to symbolize dignity and magnificence on family coats of arms and national flags. The bald eagle, for example, is a national symbol for the United States, representing both strength and freedom. Despite such respect, several species of raptors have in the past been hunted to near extinction. Compounding their decline was the widespread use of organic pesticides that poisoned raptor habitats. Fortunately, conservation efforts have been successful in rebuilding some threatened populations.

Raptor biology

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.

KEY TERMS

Carrion— A dead animal carcass, left over from the kill of a predator or dying from natural causes.

Diurnal— Refers to animals that are mainly active in the daylight hours.

Falconiformes— The taxonomic order of birds that includes eagles, hawks, vultures, falcons, buzzards, and condors. All members of this group are raptors.

Nocturnal— Animal foraging or hunting activity exclusively at night.

Raptor— A bird of prey. Raptors have feet adaptive for seizing, and a beak designed for tearing. Sexual dimorphism—The occurrence of marked differences in coloration, size, or shape between males and females of the same species.

Strigiformes— The taxonomic order of birds comprised of owls. Owls are nocturnal raptors, or birds of prey.

Talon— The extremely sharp, keratinous extensions at the end of raptor claws that function in prey capture and defense.

Raptor conservation

Raptors have been greatly affected by human activity. Certain birds of prey have become threatened or endangered as the result of hunting, pollution, and habitat destruction. As many as 18 raptor species have been labeled as endangered or threatened in the United States. However, efforts to restrict hunting, create and protect preserves and wildlife refuges, decreased pollution, and captive breeding and rehabilitation efforts have helped some raptor populations to survive and regain their numbers. In the 1940s, heavy use of the pesticide DDT caused a drastic decline in bald eagle populations. By 1974, it was estimated that only 700 breeding pairs of bald eagle remained. After DDT was banned, numbers of bald eagles rose. Similarly, when the use of another potent pesticide was banned, numbers rose. During the same period, legislation was passed that prohibited poaching of bald eagles and disturbance of their nests. As a result, there are believed to be more than four thousand breeding pairs of bald eagles in the lower 48 states alone. However, given this success, several species, such as the California condor, remain endangered. One such example is. At one period, there were thousands of California condors. By 1939, however, the number of condors fell to less than 100. By 1982, fewer than 25 remained in the wild. Their decline was attributed to habitat loss, organic pesticide poisoning, and electrocution on high voltage wires. Due to their slow reproductive rate, these problems were compounded. Conservationists feared the extinction of the species and organized a huge effort to breed more California condors before they were lost. Because of captive breeding programs, over 100 California condors live, and some have been released back into the wild where it is hoped they will survive to reproduce on their own.