Naturally, for creatures who move in a fundamentally more fully three dimensional universe than we do a good sense of balance is very important. Birds start using calls early in their lives, in some species even before they are hatched. Quail chicks use calls to communicate with each other and their mother from inside their eggs. They are able this way to synchronise their hatching so that they all emerge from the eggs within the space of a couple of hours. Pelican chicks tell their mum if they are too hot or cold from inside the eggs.
Chicks also listen to their parents while inside the eggs.
This way they come to recognise their parents even before emerging form the eggs. Some birds such as Mallards have special maternal calls that they give while incubating the eggs so that after hatching the mother only has to give this call to have the chicks rush to her for protection. Sound is often more important than sight in parent-offspring recognition. Experiments have also shown that, in colony nesting birds at least young birds can recognise their own parents by their calls alone, though they all sound the same to us. Not all young birds learn to recognise their parents or vice versa immediately.