What birds can fly immediately after being hatched?

The mound builders, a family of birds inhabiting Australia and certain
South Sea Islands, are unique in that the young are hatched fully
feathered and are able to fly and live an independent life from the
moment they emerge from the shell.

These birds are called megapodes because of their large feet. Most
species lay their eggs in large mounds constructed of loose soil,
leaves, grass, twigs, etc. The mounds are ten to twelve feet high and
contain several truckloads of material.

After the eggs are deposited they are left to hatch out by the heat of
the decaying vegetable matter. The brush turkeys are the most common of
the mound builders. One species of megapodes lays its eggs in the sand
on the seashore and leaves them to be hatched by the heat of the sun.