Birds –
* They are a class of vertebrate animals, bipedal, warm-blooded, oviparous, mainly characterized by having penas.As birds vary greatly in size, from tiny hummingbirds to large species such as ostrich and emu.
* Note that all birds are birds, but not all birds are birds.
* The birds are included in the order Passeriformes, being the richest order, ie with the highest number of species within the group of birds.