The hole is the door of the nest. A third bird is called the oven bird. The oven bird makes a nest that is very solid. The nest is made of mud. The oven bird forms the mud into the shape of an oven and then lets it dry in the sun. The sun bakes the mud, making it very hard. Not all birds make their homes in branches. Some birds build their nests on the ground, while others bury their eggs under the ground. And some birds do not build nests at all. So when you look for nests and eggs in the branches of the trees and bushes, remember that some nests may be right under your feet.