Learn About Eagles from A to Z
Take your eagle knowledge to new heights
Accipitriformes: An order that includes most diurnal birds of prey including eagles, hawks, and old-world vultures.
Accipiter: A breed of hawks distinguished by short, broad wings and relatively long legs, adapted for fast flight in wooded country such as Sharp-shinned Hawks, Cooper’s Hawks, and Northern Goshawks.
Air sac: A part of the complex respiratory system in birds, the air sac is the air-filled cavities in the lungs and bones that help with breathing and temperature regulation.
Altricial: Birds that hatch with little to no downy feathers and are relatively immobile. These young birds must be fed by adults and need time to develop before leaving the nest. Most perching birds are altricial, which is the opposite of precocial (meaning they are able to feed themselves). Eagles are considered semi-altricial.
Alula: The specialized structure of the upper leading edge of a bird’s wing that consists of a tuft of short, stiff flight feathers attached to the movable first wing digit corresponding to the thumb and that facilitates flight, landing, maneuverability at slow speeds and keeps the bird from stalling.
Anklet: A leather band, or bracelet, worn by captive birds of prey that fastens around their leg.
Asynchronous: When a clutch of eggs hatches over a period of several days rather than all at once.
Axillary: The area under the wing next to the body.
Bate: The sudden movement of a raptor off a handler’s arm or its perch.
Bergmann’s Rule: When examining mammals and birds, individuals of a particular species in colder climates (further from the equator) tend to have greater body mass than individuals in warmer climates (closer to the equator). For example, Bald Eagles are larger in Alaska than eagles found along the Gulf Coast of the United States.
Bi-colored beak: A beak that has two different colors. Immature Bald Eagles have a bi-colored beak which is dark, blue-black, and lighter toward the base. As juvenile Bald Eagles mature the beak color gets lighter from the base outward, gradually becoming the light yellow of the adult Bald Eagle.
Blood feather: A new feather still growing \that has nerves and blood supply in the shaft. A blood feather, sometimes called a pin feather, has not yet hardened and is more prone to breakage.
Booted Eagles: One of the four major groups of eagles, also known as True Eagles, Booted Eagles have feathers on their entire legs, including from their tarsometatarsi (long bone in their leg) to their toes. Golden Eagles are part of the Booted Eagle family.
Branching: When eaglets move from the nest to a branch and flap their wings before jumping off. This common behavior serves to strengthen flight muscles and acclimate the eaglet to life outside the nest.
Brood patch: A bare area of skin that develops on adult birds who are incubating eggs that allows blood vessels in the skin to have more direct contact with the egg in order to maintain body temperature.
Bumblefoot: A condition typified by sores on the bottom of a bird’s foot caused by infection and inflammatory reaction. It is somewhat analogous to bedsores in humans and can be caused by an inappropriate or insufficient variety of perches, poor nutrition, obesity, inactivity, or a compromised immune system. Captive birds are more susceptible to bumblefoot than non-captive birds.
Buteo: A breed of hawks typified by long, broad, rounded wings and shorter, rounded tails. This includes ed-tailed, rough-legged, broad-winged, and red-shouldered hawks that are often seen soaring with their wings and tails spread.
Carpal: Refers to the wrist area.
Carrion: The dead and decaying flesh of animals (often found along roadsides), which may serve as food for scavengers or opportunistic predators.
Carnivore: An animal that derives its energy and nutrient requirements from a diet consisting of animal tissue, whether through hunting or scavenging.
Cere: Fleshy region at the base of the beak that surrounds the nostrils.
Cervical vertebrae: Vertebrae (bones) in the neck region. Raptors have 14 cervical vertebrae that allow them to turn their necks 180 degrees or more. In contrast, humans have only 7 cervical vertebrae and can rotate their heads just 70-90 degrees in either direction.
Cloaca: Posterior opening common to the intestinal, urinary and generative systems. In birds, this is also called the vent.
Cloacal kiss: In copulation, when male and female cloacas touch and sperm is transferred from male to female.
Clutch: A group of eggs laid in a given breeding season.
Complete migration: When all individuals of a species leave the breeding range during the nonbreeding season.
Copulation: Also called mating, it is the act that accomplishes the transfer of sperm from male to female. See cloacal kiss.
Congress: A large gathering of eagles. Also referred to as a convocation.
Coot: Medium-sized water bird that is part of the rail family. They have black plumage and are a favorite food of Bald Eagles, especially during fall migration.
Coping: Trimming or shaping the beak or talons. Coping is often necessary for captive birds of prey that have a nutrient-rich diet and may incur less wear on their beak than wild birds.
Coverts: Contour feathers found on the body. They are usually named for their location on the bird, e.g. primary coverts.
Crepuscular: Active at dawn and dusk.
Crop: Widening in the esophagus where a hawk, eagle, falcon, or vulture can store food. It is also referred to as the craw.
Deck feathers: The two central tail feathers.
Dihedral: A wing position used by some birds when soaring. A dihedral resembles a V, with wingtips raised horizontally. Turkey vultures commonly soar in a dihedral wing position.
Diurnal: An animal or bird that is active during the day. Eagles and many raptors are diurnal.
Eaglet: A young eagle from days after hatching (hatchling) up to the period before the first flight (fledgling).
Egg tooth: Hatchling eaglets have a special notch on their beak to facilitate pipping – or the process of chipping out of the egg. This pip tooth or egg tooth falls off several days after hatching.
Endangered species: A species that has been identified as under threat of extinction or extirpation—which means a species no longer exists in a native area.
Extinction: The complete loss of a species from the planet.
Extirpation: The loss of a species from a particular part of its natural range.
Eyrie: An eagle nest site. An eyrie is typically elevated high in a tree or on a cliff ledge.
Facial disc: A concave circle of feathers on the face of owls and harriers that helps the bird locate prey by directing sound to the ears.
Falcon: A member of the family Falconidae and the genus (breed) Falco. Falcons are characterized by long pointed wings, dark eyes, and medium to long tails. Falcon species include Peregrine Falcons, Kestrels, Merlins and Prairie Falcons, and many others.
Falconry: The ancient sport of hunting with a trained raptor
Feaking: The act of rubbing the beak against a surface for cleaning or maintaining beak shape. This is often done after eating.
Fish Eagle: Also called sea eagles, they are one of the four major groups of eagles and feed primarily on fish.
Fledge: The act of a young bird taking its first flight from the nest.
Fledgling: An immature bird who has flown at least once but remains under the care of adult birds.
Flight feathers: These consist of the wing feathers (the primaries and secondaries collectively called remiges) and the tail feathers (retrices).
Fret Marks: Lines across the feathers that develop as a result of the bird being malnourished, ill, or stressed while the feathers were growing. They are also called stress marks/bars.
Genus: The taxonomic classification just above species. A group of species exhibiting common characteristics. Golden Eagles are in the genus Aguila. Bald Eagles are in the genus Haliaeetus.
Gizzard: Part of the stomach in many birds that contains small stones or gravel, which is used to break down food mechanically. Raptors do not use the gizzard to digest their food and instead digest food with powerful stomach acids.
Glide: To coast downward in flight without flapping. This is the opposite of soaring.
Hackles: The feathers on the back of the head that raise when the bird is in a stressed or aggressive state.
Hallux: The largest toe which assists in perching and points backward in most bird species.
Hatchling: A baby bird a few days after hatching or breaking out of the eggshell.
Harpy Eagles: Refers to a particular species of eagle, Harpia harpyja, found in Central America. The harpy eagle group also includes the Papuan Eagle, Harpyopsis novaeguineae, of New Guinea.
Home range: An area that an animal may use to find food. It is usually larger than their breeding territory and not defended as such.
Hopscotch: A migration pattern in which the northernmost birds migrate farther south than some year-round residents of the same species. For example, Red-Tailed hawks in Minnesota may stay year-round, while some of the birds from Canada migrate south of Minnesota.
Hovering: Refers to flap flying in place which is very energy-intensive and most commonly seen in kestrels and rough-legged hawks. (contrast with Kiting)
Imping: The process of repairing a flight feather by joining the shafts of the broken feather to the shaft of an intact feather (which may be a previously molted feather)bs.
Imprinting: A psychological process where a young bird or animal identifies with a figure present early in life. When birds raised by humans form bonds with humans and may therefore be unable to form pair bonds with their own species. Imprinted birds are typically unable to be released to the wild.
Irruption: Sporadic migration pattern which occurs when there is a lack of prey in a typical range.
Jess: A strap (traditionally leather) that attaches to the anklet of a captive bird of prey.
Keel: The ridge of the breast bone where the flight muscles attach.
Kettle: A group of birds using a thermal (rising pocket of air) to gain elevation.
Kite or Kiting: Flying in one place without flapping (contrast with Hovering).
Leading edge: A term used by bird watchers and others to describe the front edge of the wing.
Leash: A rope attached to the jess or jess extender on a captive bird of prey. The leash is either held by the handler or used to tether the bird to a perch.
Lore(s): The region between the eyes and nostrils of a bird, reptile, or amphibian.
Lure: A falconry tool that is used to train a bird of prey: Food is attached to the lure which is then swung around on a long rope and thrown for the raptor to seize. Lures are typically made of leather cut in the shape of a bird.
Mantle: A behavior of raptors characterized by spreading the wings and tail to defend food.
Mew: An enclosure or housing area for captive birds of prey.
Migration: The seasonal movement of animals between breeding and non-breeding ranges.
Molt: The natural process of replacing feathers: Raptors molt once a year, usually in spring and summer. They do not lose all their flight feathers at one time and are never rendered flightless by a molt. It can take up to four years for an eagle to complete a molt.
Morph: A variation within a species such as a color morph. For example, rough-legged hawks have two color morphs; light and dark. Eastern screech owls have two color morphs; rufous (reddish) and gray.
Mutes: Bodily waste of a raptor that includes urine and feces. The three parts to a mute are:
- Fecal: the semi-solid mass which is frequently dark in color.
- Urate: the white, chalky material is the crystalline uric acid that is the result of protein metabolism.
- Urine: the clear water that flushes the waste from the system.
Nape: The back of a bird’s neck. On Golden Eagles, this area exhibits a golden color.
Nest site fidelity: The tendency of eagles and some other birds to return to the same nest site each breeding season.
Nictitating membrane: Also known as “the third eyelid,” it closes from the interior edge out to the side and cleans and protects the eye.
Nocturnal: An animal or bird that is active at night.
Opportunistic predator: A predation pattern of animals that hunt when necessary and scavenge when carrion is available.
Ornithology: The study of birds.
Osprey: A raptor that feeds almost exclusively on fish and is sometimes called a fish hawk. Osprey can catch fish in deeper water than Bald Eagles because they can dive below the surface of the water. An osprey’s toe is reversible, allowing it to grasp its prey with two toes in front and two behind or three toes in front and one behind (as an eagle would grasp).
Partial Migration: Some members of a population leave the breeding range during the nonbreeding season while others remain in the breeding range year-round.
Passerine: A bird of the order Passeriformes, which includes more than half of all bird species. They are sometimes known as perching birds or, less accurately, songbirds.
Patagium: The leading edge of the wing between the shoulder and the wrist. In Red-Tailed Hawks, the dark patagial line is one of the best field marks.
Pellet: Indigestible food regurgitated by a bird; In the case of eagles, a pellet consists only of fur or feathers. Other raptors, such as owls, also regurgitate bones in their pellets along with the fur of animals they consume. There are no bones in pellets.
Pipping (pip): Breaking through the eggshell by a hatchling. The first break is called a pip. Hatchling eaglets have a special notch on their beak, an egg tooth, to facilitate pipping.
Photo period: The period of daylight every 24 hours; varies seasonally except at the equator. In the northern hemisphere, the photoperiod is longest on June 21st (also called the Summer Solstice)and shortest on December 21st (the Winter Solstice). For many birds, the timing of biological processes such as molting and breeding can be triggered by changes in the photoperiod.
Plumage: The feathers as well as the color and pattern of a bird’s feathers. Many species may have different plumages based on gender or age.
Precocial: Young eagles that are born or hatched with some downy feathers and are mobile and able to flee or defend themselves from predators.
Predator: An animal or bird that hunts and feeds on other living organisms.
Preening: Grooming of the feathers where an eagle pulls its beak down the feather to clean and straighten it: Preening is a behavior of birds in a relaxed state.
Prey: An organism that is hunted by predators.
Primaries: The largest flight feathers. Often described as “fingertips,” they are the outer ten flight feathers on the wing numbered from the wrist outward.
Race: A subspecies. Although races are distinct within species, they can interbreed. It was previously thought that there were two distinct races of Bald Eagles, a northern and a southern race, due to the significant size differences between the northern and southern populations. Few sources refer to different races of the Bald Eagle today, however, there are three distinct races of Peregrine Falcon in the US.
Radius: One of the bones in the wing extending from the wrist to the elbow.
Raptor: A bird of prey with keen eyesight, a hooked beak, and strong talons. The word derives from the French “rapere”, which means to seize and carry off.
Remiges: The flight feathers located on the wings
Retrices: The flight feathers located on the tail
Rouse: When the bird raises all her feathers and shakes. This is often a sign of contentment.
Scavenger: An animal that feeds on dead or decaying animal or plant material. For example, vultures scavenge animal material and eagles and other predators will sometimes scavenge when given the opportunity.
Secondaries: The flight feathers that attach from the wrist to the elbow.
Semi-altricial: An animal or bird (includes eagles) that is born or hatched and is not yet ready to survive independently.
Siblicide: The killing of a sibling. Eaglets and other young raptors sometimes engage in siblicide, especially when food is scarce.
Snake Eagles: One of the four major groups of eagles around the world, these eagles feed primarily on snakes. This group includes Short-toed Snake Eagle (Circaetus gallicus), Black-chested Snake Eagle (Circaetus pectoralis), and Brown Snake Eagle (Circaetus cinereus)
Soar: Upward flight without flapping. This is often done by making use of a thermal or column of rising warm air. Once at the top of a thermal, the raptor will often glide to another thermal. Wings are usually fully extended in a soar.
Species: A grouping of birds or animals that can interbreed. A species name is typically denoted with a two-word Latin name that identifies both the genus and the species. Bald Eagles are Haliaeetus leucocephalus. Golden Eagles are Aquila chrysaetos.
Stoop: Fast dive by a bird of prey with the wings tucked close to the body. This is usually done in pursuit of prey.
Supraorbital ridge: The bony protuberance above the eye socket. This ridge helps shade and protect the eye and gives raptors their fierce look.
Talon: A sharp, pointed claw on an eagle’s toe. Each foot has four talons
Tarsometatarsus (pl. Tarsometatarsi): A bone that is only found in the lower leg of birds and certain dinosaurs. The tarsometatarsus is formed from the fusion of several bones found in other types of animals and homologous to the mammalian tarsal (ankle) and metatarsal (foot) bones. The tarsometatarsus of birds is often referred to as just the tarsus or metatarsus.
Telemetry: The science and technology of automatic measurement and transmission of data by radio, satellite, or other means from remote sources to receiving stations for recording and analysis.
Territory: The area around the nest that is defended by the eagles.
Thermal: A column of warm air that eagles use to soar.
Trailing edge: The back edge of the wing.
Transmitter: A device that can be attached to an animal or bird to send global positioning data about the animal’s location. This is often used to track the movement and migration of wildlife.
Tri-colored beak: Golden Eagles have a distinctly colored beak that is dark at the tip, bluish-gray in the middle, and light at the base. The tri-color does not include the yellow cere at the base of the beak, which is not part of the beak.
True Eagles: One of the four major groups of eagles, True or booted eagles have feathers on their entire leg, including on their tarsometatarsi, and up to their toes. Golden Eagles are part of the true or booted eagle family.
Ulna: The bone in the wing that extends from the wrist to the elbow. The secondary flight feathers attach to the ulna.
Vent: The pening on a bird through which bodily waste is excreted. Both solid waste and liquid waste are excreted together and are referred to as mutes.
Weathering: The practice of allowing captive birds of prey time outdoors.