Birds (Aves) are a group of endothermic vertebrates, 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 cm (2 in) bee hummingbird to the 2.75 m (9 ft) ostrich. They rank as the world’s most numerically-successful class of tetrapods, with approximately ten thousand living species, more than half of these being passerines, sometimes known as perching birds. Birds have wings which are more or less developed depending on the species; the only known groups without wings are the extinct moa and elephant birds. Wings, which evolved from forelimbs, gave birds the ability to fly, although further evolution has led to the loss of flight in flightless birds, including ratites, penguins, and diverse endemic island species of birds. 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. Reverse genetic engineering and the fossil record both demonstrate that birds are modern feathered dinosaurs, having evolved from earlier feathered dinosaurs within the theropod group, which are traditionally placed within the saurischian dinosaurs. The closest living relatives of birds are the crocodilians. Primitive bird-like dinosaurs that lie outside class Aves proper, in the broader group Avialae, have been found dating back to the mid-Jurassic period, around 170 million years ago.
Swans. - Two swans: white and black.
Play now!

Added 2 weeks ago by Grażyna


Colorful parrots. - Paradise birds in the garden.
Play now!
Colorful parrots.

Added month ago by Grażyna


Common evening - Enjoying the sunset by small friends
Play now!
Common evening

Added year ago by ewunia x

585 3

Princess anime - Beautiful anime princess, dressed in a rich dress. Orange dress with flounces and ruffles. A beautif
Play now!
Princess anime

Added year ago by Ariadna


bird dance - birds, dance, feet, feathers
Play now!
bird dance

Added year ago by wieslawa

150 2