What if? You can't really do anything, just don't mess with the eggs or nest.
A Cukoo Bird builds it's nest in a chimney
if you like bird feces
nest
cattle bird
The Weaver builds a nest out of grasses, with the entrance at the bottom.
Hummingbirds. The nest of the bee hummingbird, the smallest bird in the world, is only 3cm in diameter.
an eagle builds a nest called an aerie
# it takes about 1-2months for a baby bird leaves its nest.
penguins don't build nests
Yes, mockingbirds do lay eggs. Typically, a female mockingbird will lay a clutch of 2-6 eggs in a nest that she builds to incubate them.
The cow bird. The cow bird lays it's eggs in another birds nest, and then when the cow bird's eggs begin to hatch, the baby cow birds will push the other birds out of the nest.