Falconids are medium-sized to large birds of prey (wingspan 55 to more than 125 cm, weight 28 to 2100 g), typically with hooked beaks, large brown eyes and a yellow cere, eyerings and feet. Falcons (Falconinae) are typically stocky birds with pointed wings, long toes with sharp talons, hooked, notched beaks, and brown, black, gray or white streaked or mottled plumage. Caracaras (Polyborinae) are smaller than falcons, have longer necks and legs than falcons, thicker, flatter talons, more rounded wings, a semi-bare face that is often brightly colored, and often glossy black plumage. Plumage of most falconids is lighter below and darker above. Individual species show variation from the basic structures that reflects the functions required by their habitat and prey. For example, the length and strength of the toes and beaks vary widely within the family and correspond to prey type. Bird predators have long toes, where as insect- and mammal-catching species have shorter, fleshier toes. Wing shape also varies; fast, open-country species have long, pointed wings, whereas forest-dwelling species have more rounded wings and longer tails.
Like other birds of prey, falconids exhibit reversed sexual size dimorphism (females are larger than males). This trait is most exaggerated in falconids that catch fast-moving prey, such as birds, and less pronounced in species that primarily eat carrion. In some species, females may also have a larger bill than males. Sexual dichromatism occurs in a few species of falconids. Male and female plumage are similar in most species, though male plumage may be somewhat brighter. Immature falconids typically exhibit plumage that is dull in color, often brownish with pale edges and more streaked than adults. Some species, such as gyrfalcons exhibit light and dark morphs. Falconids molt once per year, and immatures of most species attain adult plumage by the first annual molt.
Traits shared with Accipitrids, the presumed sister taxa of falconids include a fleshy cere covering the base of a strongly hooked beak, strong hallux (hind toe) opposing three forward toes, habit of capturing prey with feet, and reversed sexual size dimorphism (female larger than male).
Traits that distinguish this group include a tubercle (small, bony projection) in the nostril, structure of the syrinx, characteristic flight-feather molt pattern, tomial teeth on bill for killing and dismantling prey, chemical composition of eggshells, reddish (rather than blue or greenish) translucence of eggs when held up to light, and habit of killing prey with the beak (rather than squeezing with the feet).
Sexual Dimorphism: female larger; sexes colored or patterned differently; male more colorful