Duck appears 64 times at rank 1607 on male pets, and this is almost certainly a registry artifact category. Most dogs named Duck were not deliberately named Duck — someone called a waddling puppy "the little duck" as an observation, and that observation became the permanent registered name before anyone chose something more formal.
The Observation-to-Name Pipeline
Duck as a dog name follows the same logic as Penguin, Waddles, and Goose — animal-comparison nicknames applied to puppies whose gait, shape, or behavior reminded the owner of another animal. A puppy that runs with splayed feet or sits with an awkward posture might get called "duck" affectionately, and the name sticks. The paperwork catches it before the formal name is decided.
When Duck Is a Real Choice
Some owners do name dogs Duck intentionally — particularly in duck-hunting households where the name is a tribute to the dog's working purpose rather than its appearance. Labrador Retrievers and Chesapeake Bay Retrievers are bred for waterfowl retrieval, and Duck on a working retriever is a genuine inside joke among hunting communities. Compare with Drake in the waterfowl naming set.
The Counter-Reading
Duck requires almost no defense in a hunting household. Elsewhere, it reads as either a charming story of accidental naming or a deliberate absurdist choice. Both are legitimate, and both are more interesting than the name suggests at first glance.