This is a header2. 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 f rom 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.
Many social species preserve knowledge across generations (culture). Birds are social, communicating with visual signals, calls, and songs, and participating in such behaviour as cooperative breeding and hunting, flocking, and mobbing of predators. The vast majority of bird species are socially (but not necessarily sexually) monogamous, usually for one breeding season at a time, sometimes for years, and rarely for life.Many social species preserve knowledge across generations (culture). Birds are social, This is smalll communicating with visual signals, calls, and songs, and participating in such behaviour as cooperative breeding and hunting, flocking, and This is an em style element marmobbing of predators. The vast majority of bird species are socially (but not necessarily sexually) monogamous, usually for one breeding season sat a time, sometimes for years, and rarely for life.
