Meaning of quack that usually use by ducks and geese

I just want to share about why the ducks and geese always quack at sky or during flying. Firstly, these animals want to communicate with other ducks and geese. The typical quack we associate with ducks is only made by female mallards and a few other duck species. Other than that, the males (drakes) make quieter, rasping sounds and do not quack. Whatever names the human give name to them, these calls are used mostly to keep family together or call ducklings closer. This is true whether the birds are on land, on water or flight. So that why the ducks and geese always quack at sky or during flying.