Swimming-bird is a term used to describe a type of bird that is able to swim in water. The most common example of this type of bird is the DUCK, which has four letters in its name. Ducks are aquatic birds that are found in both fresh and saltwater habitats around the world. They are known for their webbed feet, which help them to swim and dive underwater. Ducks are also known for their wide variety of vocalizations, which they use to communicate with each other.