To "have one's ducks in a row" means that the person is doing a good job and has all of his or her duties taken care of in an efficient and timely manner. Phrases involving our web-footed friends, including "nice day for a duck" (meaning rainy weather) and "like water off a duck's back" (meaning having no effect), have been common in English for hundreds of years. "To have one's ducks in a row," however, seems to be a fairly recent coinage. The first appearance of the phrase noted in Random House Historical Dictionary of American Slang is in 1979, in Stephen King's novel "The Stand." The related "line up one's ducks" appears only a year earlier, in 1978.
But why a duck? to echo the Marx Brothers. It's possible that the phrase began as a reference to the lines of little metal ducks used as targets in carnival shooting galleries. A more benevolent explanation would be that "to have one's ducks in a row" refers to the common sight of a mother duck leading a troop of her ducklings in an orderly row.
- The Word Detective