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. In Herring Gulls, about 5 days pass before this recognition takes place, while Kittiwakes take up to 5 weeks for recognition to register.
Birds also distinguish their mates by call.
Birds use sounds other than those created by their vocal chords. Sounds can be created by stamping as in Coots, or by clacking the mandibles together as in Frigate birds, Albatrosses and Storks. Birds also use their wings to create sounds, simply by clapping them together as the wood pigeon or by having modified feathers which vibrate at a set frequency when exposed. Snipe use this during courting. Two feathers on either side of the tail vibrate as the bird falls out of the sky.