Accipitriformes – a taxonomical order that includes most diurnal birds of prey including eagles, hawks and old world vultures

Accipter –  genus of hawks in the taxonomic family Accipitridae characterized by broad, rounded wings; includes Sharp-shinned Hawks, Cooper’s Hawks and Northern Goshawks

Air sac –  a part of the complex respiratory system in birds; air-filled cavities in the lungs and bones; aids in breathing and temperature regulation

Altricial – describes birds that hatch with little to no downy feathers and are relatively immobile, such young must be fed by adults and need time to develop before leaving the nest. Most passerines are altricial. Altricial is the opposite of precocial. Eagles are considered semi-altricial.

Alula – Also called bastard wing, this projection on the front edge of the wing typically has three to five feathers which can be spread when flying slowly to keep the bird from stalling.  The alula is the first digit, anatomically analogous to the thumb.

Anklet  – Part of the equipment worn by captive birds of prey, the anklet is a leather band that fastens around the leg. Also referred to as bracelet. Jesses attach to the anklet.

Asynchronous  – Describes hatching in a clutch of eggs that occurs over a period of several days rather than all the eggs hatching together

Axillary  – the area under the wing, next to the body


Bate  – sudden movement of a raptor off a handler’s arm or its perch.

Bergmann’s Rule – Bergmann’s rule states that among mammals and birds, individuals of a particular species in colder areas (further from the equator) tend to have greater body mass than individuals in warmer climates (closer to the equator). One example is that bald eagles are larger in Alaska than those found along the Gulf Coast of the United States.

Bi-colored beak – describes a beak of two 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 in that has nerves and blood supply in the shaft. A blood feather has not yet hardened and is more prone to breakage. Sometimes called a pin feather.

Booted eagles –  one of the four major groups of eagles; Booted eagles have feathers on their entire leg, including on their tarsometatarsi, up to their toes. Golden eagles are part of the booted eagle family. Also called True eagles.

Branching – a behavior common in eaglets just before fledging. In branching, eaglets move from the nest to a branch and flap their wings and jump off the branch. This 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 more direct contact with the egg to maintain it at 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 inappropriate or insufficient variety of perches, poor nutrition, obesity and/or inactivity or a compromised immune system. Captive birds are more susceptible to bumblefoot than non-captive birds.

Buteo  – genus of hawks typified by long, broad, rounded wings and shorter, rounded tails; includes red-tailed, rough-legged, broad-winged and red-shouldered hawks that are often seen soaring with wings and tails spread


Carpal  – referring to the wrist area

Carrion – dead and decaying flesh of animals; 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 predation or scavenging

Cere  – fleshy region at the base of the beak that surrounds the nostrils. See Photo

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, also called the vent.

Cloacal kiss – in copulation, when male and female cloacas touch and sperm is transferred from male to female

Clutch –  group of eggs laid in a given breeding season

Complete migration – all individuals of a species leave the breeding range during nonbreeding season

Copulation – mating, act that accomplishes the transfer of sperm from male to female; see cloacal kiss

Congress – a term that refers to a large gathering of eagles.  Also referred to as a convocation.

Coot  – part of the rail family; small, all black plumage; 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 body, 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; sometimes 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 wings tips raised from horizontal. e.g. Turkey vultures commonly soar in a dihedral wing position.

Diurnal  – describes an animal or bird that is active during the day; Eagles and many raptors are diurnal, indicating that they hunt during the day.


Eaglet – a young eagle, typically describes an eagle some 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. 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; In the United States, the US Fish and Wildlife Service  maintains an official list of species that are considered endangered and threatened or of special concern. Internationally, the International Union for the Conservation of Nature (IUCN) maintains listings of more than 49,000 species, subspecies and varieties of flora and fauna and places each in a category based on the level of threats that species is facing in the wild.

Extinction – the complete loss of a species from the planet

Extirpation – the loss of a species from a particular part of its natural range; e.g The bald eagle was nearly extirpated from the continental US. Populations in Alaska and Canada remained healthy even while bald eagles were rare in the lower 48 states.

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 help the bird to locate prey by directing sound to the ears

Falcon – a member of the family Falconidae and the genus Falco, characterized by long pointed wings, dark eyes and medium to long tails along with the other raptor characteristics of hooked beaks, sharp talons, and keen eyesight.  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, often done after eating.

Fish eagle – eagles that feed primarily on fish, one of the four major groups of eagles, also called sea eagles

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 who remains under the care of adult birds.

Flight feathers  – consist of the wing feathers (the primaries and secondaries collectively called remiges) and the tail feathers (retrices)

Fret Marks – lines across the feathers which develop as a result of the bird being malnourished, ill or stressed while those feathers were growing; 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 Halieaatus.

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.  Instead, raptors digest food with powerful stomach acids.

Glide – coasting downward in flight without flapping.  It is the opposite of Soar.


Hackles – feathers on the back of the head, raised when the bird is in a stressed or aggressive state

Hallux – the largest toe, which points backwards in most bird species, assists in perching

Hatchling – refers to bird in the few days just after hatching, or breaking out of the eggshell

Harpy eagles – refers to a particular species of eagle, Harpia harpyja, found in Central America; Also refers to one of the four major groups of eagles around the world. The harpy eagle group also includes the Papuan Eagle, Harpyopsis novaeguineae, of New Guinea.

Home range – area that an animal may use to find food; usually larger than their breeding territory and not defended as such

Hopscotch – describes a particular migration pattern in which the northern most birds migrate farther south than some year round residents of the same species. As an example, red-tailed hawks in Minnesota may stay year round, while some of the birds from Canada migrate to an area south of Minnesota.

Hovering – flap flying in place; hoveringis 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 broken feather to an intact feather (which may be a previously molted feather) by joining the two feather shafts

Imprinting – describes a psychological process where a young bird or animal identifies with a figure present early in life; birds raised by humans form inappropriate bonds with humans and may later be unable to form pair bonds with their own species; imprinted birds are typically unable to be released to the wild

Irruption – describes sporadic migration which occurs only in some years, usually due to lack of prey availability in typical range


Jess – strap (traditionally leather) that attaches to the anklet of a captive bird of prey. See Photo


Keel – 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 – 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. See Photo

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; often 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 tend to molt symmetrically meaning if they lose the third primary on the right, they also lose the third primary on the left.  Raptors 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 with in a species, such as a color morph; e.g. 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;  There are three parts to a mute: fecal – the semi-solid mass, frequently this is dark in color. Urate – white, chalky material – the crystalline uric acid that is the result of protein metabolism. Urine – 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 – describes 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”; closes from the interior edge out to the side; The membrane cleans and protects the eye. See Photo where membrane is partially covering the eyeball and appears as a cloudy film over the eye.

Nocturnal – describes an animal or bird that is active at night;


Opportunistic predator – describes predation pattern of animals that hunt when necessary and scavenge when carrion is available

Ornithology – the study of birds

OspreyPadion haliaetus; a raptor that feeds almost exclusively on fish, sometimes called a fish hawk; Osprey are able to 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 them to grasp their 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 nonbreeding season while others remain in the breeding range year round

Passerine – bird of the order Passeriformes, which includes more than half of all bird species. Sometimes known as perching birds or, less accurately, as 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 pellet along with the fur of animals they consume.  See Photo of an eagle pellet – note no bones in the pellet.

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 in every 24 hours; varies seasonally except at the equator. In the northern hemisphere, the photo period is longest on June 21st and shortest on December 21st. For many birds, the timing of biologic processes such as molting and breeding can be triggered by changes in the photo period.

Plumage –  refers to the feathers as well as to the color and pattern of a bird’s feathers. Many species may have different plumages based on gender or age.

Precocial – young that are born or hatched with some downy feathers and are mobile and able to flee or defend themselves from predators; opposite of altricial, describing young that need time to mature before leaving the nest.

Predator – an animal or bird that hunts and feeds on other living organisms

Preening – grooming of the feathers, pulling the 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 predator, food source for predators

Primaries – the largest flight feathers; the outer ten flight feathers on the wing, numbered from the wrist outward; often described as ‘finger tips’ when observed on a bird in flight



Race –  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. e.g. 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; from the French rapere, to seize and carry off

Remiges – flight feathers located on the wings

Retrices  – flight feathers located on the tail

Rouse – when the bird raises all her feathers and shakes, a sign of contentment


Scavenger – an animal that feeds on dead or decaying animal or plant material; vultures scavenge animal material, eagles and other predators will sometimes scavenge given the opportunity

Secondaries  – flight feathers that attach from the wrist to the elbow

Sea eagles – see Fish eagles

Semi-altricial – an animal or bird that is born or hatched not yet ready to survive independently, but has some fur or downy feathers; eagles are semi-altricial

Siblicide – the killing of a sibling; eaglets and other young raptors sometimes engage in silicide, particularly when food is scarce

Snake eagles – one of the four major groups of eagles around the world; feed primarily on snakes; 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; often done making use of a thermal, a 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, usually in pursuit of prey

Supraorbital ridge – the boney 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 – area around the nest defended by the eagles; also breeding territory

Thermal – column of warm air used in soaring

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; used to track 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. The cere is not part of the beak. See Photo

True eagles – one of the four major groups of eagles; True or booted eagles have feathers on their entire leg, including on their tarsometatarsi, up to their toes. Golden eagles are part of the true or booted eagle family.


Ulna – bone in the wing extending from the wrist to the elbow; the secondary flight feathers attach to the ulna


Vent – opening on a bird through which bodily waste is excreted; both solid waste and liquid waste are excreted together and are referred to as mutes; also known as the cloaca


Weathering – the practice of allowing captive birds of prey time outdoors