Is the birds born?

Bird is not born, but oyster.Birds, such animals, are very single. The current known birds are basically eggs, and no one is viviparous.There are generally two characteristics of eggs. One is that all nutrients during the incubation of the chicks are absorbed through the yolk, and they will be fed by pro -birds after hatching.The other is that the incubation requires a certain temperature and time, otherwise the birds cannot be born.