Answer:
The birds are oviparous in nature and produces eggs that are hatched later by the parent. the egg hatching require proper heat and protection from the external enemy.
The egg shell is the hard covering of the egg of the bird that is made of the calcium. The egg shell protect the egg from the external environment. The calcium layer for the egg shell formation is obtained by the oseteoclast property of the cells.
The environment would probably be a grass land or rich forest
