Birds 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 lightweight but strong skeleton. Birds live worldwide and range in size from the 5 cm bee hummingbird to the 2.75 m ostrich. They rank as the class of tetrapods with the most living…
![Birds From Around the World](https://latinosforafreeamerica.org/wp-content/uploads/2016/06/common-redstart-phoenicurus-phoenicurus-bird-garden-2.jpg)