Body language, the splashing of water, nipping, and quacking.
Quacking at eachother
you can communicate by mailing letters and the Internet
In what way? Do you mean in duck language? Please clarify the question. Sure they can. Hang around a group long enough and they will recognize you. Feed them and they will love you. You can communicate with a duck by watching their body language and you communicate back by using your body language.
To communicate, lions sniff each other and roar.
to communicate with others
No.
Respectfully
A duck's sound is often referred to as a "quack." Ducks communicate with a variety of vocalizations, including quacks, squawks, and whistles. The quack is the most recognizable sound associated with ducks.
the ability to communicate with others
so you can communicate with others
to be able to communicate with others
It means that you can communicate with others with your mind.