Males of most temperate-zone ducks have bright, species-specific plumages, quite different from the drab plumages of females, many of which look very similar to one another. But these bright feathers are displayed from fall to early summer, and they are replaced during midsummer by a dull, female-like basic plumage (often called “eclipse” plumage). Displaying “breeding” plumage in fall, winter and spring and “nonbreeding” plumage in summer seems quite reversed from the situation in other birds, and in fact it is.
Almost as soon as the flocks arrive on their wintering grounds, the urge to mate kicks in, and the males begin to court the females. Those that arrive early wait until they have molted, but those that arrive late can begin the process immediately. Male ducks all have distinctive displays, which, coupled with their bright, species-specific colors, produce a dazzling show. Behavior involved in mating, both aggression and courtship display, is at its best in groups, with multiple individuals of both sexes.
Most male dabbling ducks have bright, contrasting markings around the head and breast and additional bright markings around their rear end. As soon as you see them display, you realize these color patterns are incorporated into the display. The displays are quite stereotyped, male Mallards, for example incorporating distinct display behaviors called Grunt-Whistle, Head-Up-Tail-Up, and Down-Up. Distinct behaviors are usually capitalized when written about in scientific literature.
Female Mallards perform head movements, bill-jabbing behavior, and characteristic vocalizations to indicate interest in copulating with a particular male. Females of most species will show aggression to males other than their mates. Copulation between pairs starts in the fall and continues through the winter into spring, when the birds return to their breeding grounds. Maintaining the pair bond seems to be the important function of this activity, which of course does not result in eggs being formed.
Displays in goldeneyes and mergansers are among the fanciest. In male goldeneyes, the head is thrown back almost onto the back, with a big splash when the feet kick back and an accompanying throaty note. In Red-breasted Mergansers, the male ends its display with tail down, back up, breast sinking into the water and neck extended upward with open beak, the whole thing reminiscent of some reptilian ancestor.
Some ducks rush along the water or fly short distances in their courtship. Buffleheads bob their heads violently up and down, fly just over the female and land by skiing on their bright pink feet, and cock both wings forward, exposing their big white patches. As part of their display, male Black Scoters also rush along the surface but with head down. A male Surf Scoter flies for 20-30 feet, wings whistling loudly, then drops feet-first into the water with wings raised. These display components are stereotyped in form and the order in which they are presented.
Because there is heavier predation on females when they are nesting, there are more male than female ducks in winter. Thus by spring there are still many unmated males. Courtship becomes even more intense, as gangs of male ducks roam around trying to find unmated females and spending much time harassing pairs to try to separate them (usually unsuccessfully). A lone female may be harassed by numerous males, and forced copulations are common at that time.
Finally, it’s time to make something of all that time spent mating. The pair heads off to wherever it is they breed, still maintaining that bond. They arrive, and the male has a fresh bunch of rivals to deter. The female quickly constructs a nest and lays her clutch of eggs, all the while shadowed by her mate. As soon as she begins to incubate, he leaves the scene and begins to hang out with other males in the same state. They typically move out into deeper water, begin their molt into basic plumage, and drop their flight feathers in preparation for growing a new set. It’s a new year in the odd annual cycle of a male duck.