The clusterduck is a waterfowl that is capable of making local, temporary, quantum clones of itself. These quantum ducks are indistinguishable from ordinary ducks, but they randomly come into existence and snuff out of existence.
It appears that the number of quantum ducks is tied to the mental state of the clusterduck. There are more when it is stressed or disturbed, and fewer when it is content. Breeding clusterducks tend not to generate quantum clones, as ducklings imprinting on them are easily confused.
Clusterducks tend to form pair bonds for life, and the drake will generate more quantum clones when his hen is raising ducklings. It is still extremely unclear how food ingested by the quantum clones winds up in the stomach of the clusterduck prime, but extensive lab testing has proven this to be so.