Beak in the context of "Preening"

Birds are a group of warm-blooded theropod dinosaurs constituting the class Aves, characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweight skeleton. Birds live worldwide and range in size from the 5.5 cm (2.2 in) bee hummingbird to the 2.8 m (9 ft 2 in) common ostrich. There are over 11,000 living species and they are split into 44 orders. More than half are passerine or "perching" birds. Birds have wings whose development varies according to species; the only known groups without wings are the extinct moa and elephant birds. Wings, which are modified forelimbs, gave birds the ability to fly, although further evolution has led to the loss of flight in some birds, including ratites, penguins, and diverse endemic island species. The digestive and respiratory systems of birds are also uniquely adapted for flight. Some bird species of aquatic environments, particularly seabirds and some waterbirds, have further evolved for swimming. The study of birds is called ornithology.

Birds evolved from earlier theropods, and thus constitute the only known living dinosaurs. Likewise, birds are considered reptiles in the modern cladistic sense of the term, and their closest living relatives are the crocodilians. Birds are descendants of the primitive avialans (whose members include Archaeopteryx) which first appeared during the Late Jurassic. According to some estimates, modern birds (Neornithes) evolved in the Late Cretaceous or between the Early and Late Cretaceous (100 Ma) and diversified dramatically around the time of the Cretaceous–Paleogene extinction event 66 million years ago, which killed off the pterosaurs and all non-ornithuran dinosaurs.

The vocal tract or speech apparatus is the cavity in human bodies and in animals where the sound produced at the sound source (larynx in mammals; syrinx in birds) is filtered.

In birds, it consists of the trachea, the syrinx, the oral cavity, the upper part of the esophagus, and the beak. In mammals, it consists of the laryngeal cavity, the pharynx, the oral cavity, and the nasal cavity.

The bird anatomy, or the physiological structure of birds' bodies, shows many unique adaptations, mostly aiding flight. Birds have a light skeletal system and light but powerful musculature which, along with circulatory and respiratory systems capable of very high metabolic rates and oxygen supply, permit the bird to fly. The development of a beak has led to evolution of a specially adapted digestive system.

In evolutionary biology, adaptive radiation is a process in which organisms diversify rapidly from an ancestral species into a multitude of new forms, particularly when a change in the environment makes new resources available, alters biotic interactions or opens new environmental niches. Starting with a single ancestor, this process results in the speciation and phenotypic adaptation of an array of species exhibiting different morphological and physiological traits. The prototypical example of adaptive radiation is finch speciation on the Galapagos ("Darwin's finches"), but examples are known from around the world.

Birds of prey or predatory birds, also known as raptors, are hypercarnivorous bird species that actively hunt and feed on other vertebrates (mainly mammals, reptiles and smaller birds). In addition to speed and strength, these predators have keen eyesight for detecting prey from a distance or during flight, strong feet with sharp talons for grasping or killing prey, and powerful, curved beaks for tearing off flesh. Although predatory birds primarily hunt live prey, many species (such as fish eagles, vultures and condors) also scavenge and eat carrion.

Although the term "bird of prey" could theoretically be taken to include all birds that actively hunt and eat other animals, ornithologists typically use the narrower definition followed in this page, excluding many piscivorous predators such as storks, cranes, herons, gulls, skuas, penguins, and kingfishers, as well as many primarily insectivorous birds such as nightjars, frogmouths, and some passerines (e.g. shrikes); omnivorous passerine birds such as crows and ravens; and opportunistic predators from predominantly frugivorous or herbivorous ratites such as cassowaries and rheas. Some extinct predatory telluravian birds had talons similar to those of modern birds of prey, including mousebird relatives (Sandcoleidae), and Messelasturidae indicating possible common descent. Some Enantiornithes also had such talons, indicating possible convergent evolution, as enanthiornithines are not considered to be true modern birds.

The clothing worn by plague doctors was intended to protect them from airborne diseases during outbreaks of bubonic plague in Europe. It is often seen as a symbol of death and disease. Contrary to popular belief, no evidence suggests that the beak mask costume was worn during the Black Death or the Middle Ages. The costume started to appear in the 17th century when physicians studied and treated plague patients.

The black swan (Cygnus atratus) is a large waterbird, a species of swan which breeds mainly in the southeast and southwest regions of Australia. Within Australia, the black swan is nomadic, with erratic migration patterns dependent on climatic conditions. It is a large bird with black plumage and a red bill. It is a monogamous breeder, with both partners sharing incubation and cygnet-rearing duties.

The black swan was introduced to various countries as an ornamental bird in the 1800s, but has managed to escape and form stable populations. Described scientifically by English naturalist John Latham in 1790, the black swan was formerly placed into a monotypic genus, Chenopis. Black swans can be found singly, or in loose companies numbering into the hundreds or even thousands. It is a popular bird in zoological gardens and bird collections, and escapees are sometimes seen outside their natural range.