Taken literally, the term bird of prey has a wide meaning that includes many birds that hunt and feed on animals and also birds that eat very small insects. Ornithology has a narrower definition of bird of prey: a bird that has very good eyesight for finding food, strong feet for holding food, and a strong curved beak for tearing flesh. Most birds of prey also have strong curved talons for catching or killing prey. An example of this difference in definition, the narrower definition excludes storks and gulls, which can eat quite large fish, partly because these birds catch and kill prey entirely with their beaks, and similarly bird-eating skuas, fish-eating penguins, and vertebrate-eating kookaburras are excluded. Birds of prey generally prey on vertebrates, which are usually quite large relative to the size of the bird. Most also eat carrion, at least occasionally, and vultures and condors eat carrion as their main food source.
The common names for various birds of prey are based on structure, but many of the traditional names do not reflect the evolutionary relationships between the groups.
Many of these English language group names originally referred to particular species encountered in Britain. As English-speaking people travelled further, the familiar names were applied to new birds with similar characteristics. Names that have generalised this way include: kite (Milvus milvus), sparrow-hawk or sparhawk (Accipiter nisus), goshawk (Accipiter gentilis), kestrel (Falco tinninculus), hobby (Falco subbuteo), harrier (simplified from "hen-harrier", Circus cyaneus), buzzard (Buteo buteo).
The taxonomy of Carl Linnaeus grouped birds (class Aves) into orders, genera, and species, with no formal ranks between genus and order. He placed all birds of prey into a single order, Accipitres, subdividing this into four genera: Vultur (vultures), Falco (eagles, hawks, falcons, etc.), Strix (owls), and Lanius (shrikes). This approach was followed by subsequent authors such as Gmelin, Latham, and Turnton.