Birds use songs to communicate. Sound waves produced by their calls travel over a long distance. Their songs attract mates or defend their territory. They can warn, point to food, or connect family. Bird calls are short and repetitive.
Each species has its own song. Some songs are intuitive, the birds just know them. Other birds learn their songs from the grown ups. The males do most of the singing.
Bird calls have to match their habitats. Ducks have low calls to be heard through the reeds. Forest birds have high notes. They need to be heard above the tree tops.