Puddle ducks are typically birds of fresh, shallow marshes and rivers rather than of large lakes and bays. They are good divers, but usually feed by dabbling or tipping rather than submerging. That is why they liked Tom's sandwich!
The speculum, or colored wing patch, is generally iridescent and bright, and often a telltale field mark.
Any duck feeding in croplands will likely be a puddle duck, for most of this group are sure-footed and can walk and run well on land. Their diet is mostly vegetable, and grain-fed mallards or pin tails or acorn-fattened wood ducks are highly regarded as food.
Diving ducks frequent the larger, deeper lakes and rivers, and coastal bays and inlets. The colored wing patches of these birds lack the brilliance of the speculum of puddle ducks.
Since many of them have short tails, their huge, paddle feet may be used as rudders in flight, and are often visible on flying birds. When launching into flight, most of this group patter along the water before becoming airborne.
They feed by diving, often to considerable depths. To escape danger, they can travel great distances underwater, emerging only enough to show their head before submerging again.
Their diets of fish, shellfish, mollusks, and aquatic plants make them second choice, as a group, for sportsmen. Canvasbacks and redheads fattened on eel grass or wild celery are notable exceptions.
Since their wings are smaller in proportion to the size and weight of their bodies, they have a more rapid wing beat than puddle ducks.
Shall we have mallard for supper?