Modern birds (subclass Neornithes) are the most recent common ancestor of all living birds (class Aves) and all its descendants.
Modern birds are characterised by feathers, a beak with no teeth (ancient birds had teeth), the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a lightweight but strong skeleton. All birds have forelimbs modified as wings and most can fly, with some exceptions including ratites, penguins, and a number of diverse endemic island species. Birds also have unique digestive and respiratory systems that are highly adapted for flight. Some birds, especially corvids and parrots, are among the most intelligent animal species; a number of bird species have been observed manufacturing and using tools, and many social species exhibit cultural transmission of knowledge across generations.
Many species of modern bird undertake long distance annual migrations, and many more perform shorter irregular movements. Birds are social; they communicate using visual signals and through calls and songs, and participate in social behaviours including cooperative breeding and hunting, flocking, and mobbing of predators. The vast majority of bird species are socially monogamous, usually for one breeding season at a time, sometimes for years, but rarely for life. Engagement in extra-pair copulations is common in some species; other species have breeding systems that are polygynous ("many females") or, rarely, polyandrous ("many males"). Eggs are usually laid in a nest and incubated by the parents. Most birds have an extended period of parental care after hatching.
Birds of prey are birds that hunt for food primarily via flight, using their keen senses, especially vision, and superb flying skills. They are defined as birds that primarily hunt vertebrates, including other birds. Their talons and beaks tend to be relatively large, powerful and adapted for tearing flesh. In most cases, the females are considerably larger than the males. The term "raptor" is derived from the Latin word rapere (meaning to seize or take by force) and may refer informally to all birds of prey, or specifically to the diurnal group. Because of their predatory lifestyle, often at the top of the food chain, they face distinct conservation concerns.
Many species of bird may be considered partly or exclusively predatory; however, in ornithology, the term "bird of prey" applies only to birds of the families listed below.