During the breeding season, both male and female mallards can become aggressive, driving off competitors to themselves or their mate by charging at them.[83] Males tend to fight more than females, and attack each other by repeatedly pecking at their rival's chest, ripping out feathers and even skin on rare occasions. Female mallards are also known to carry out 'inciting displays', which encourages other ducks in the flock to begin fighting.[84] It is possible that this behaviour allows the female to evaluate the strength of potential partners.[85]
Most people's first observations of duck behavior probably are of Mallard courtship. Mallards perform in the fall and winter as well as the spring, so there is plenty of opportunity to watch their displays. They are also often rather tame, and perform in the open -- this is a good thing since, while frequent, their displays are subtle and brief. Males swimming in the presence of females may be seen shaking their heads (head-shake display) and tails (tail-shake), often doing the former with their breasts held clear of the water and their necks outstretched. They also raise their wingtips, heads and tails briefly and then swim with their necks outstretched and held close to the water (head-up-tail-up). Groups of four to five males may swim around females, arching their necks, whistling, then lowering their bills below the water surface and jerking their bills up to their breasts while spurting water toward the preferred female (water-flick or grunt-whistle). The water-flick may take only a fraction of a second to complete. The drakes in male groups give short, nasal "raeb-raeb" (two-syllable) calls, and short high-pitched whistles.
Female Mallards and other female ducks often demonstrate (inciting displays) and call to provoke males to attack other males or females. In some circumstances these displays may allow the female to observe the performance of males and to evaluate them as potential mates. To elicit displays from a group of males, a female Mallard may swim with her neck outstretched and her head just above the water (nod-swimming). When a strange male approaches a female Mallard, she often will do an inciting display, swimming after her preferred mate while producing a rapid staccato series of quacks and flicking her beak back and downward to the side. As pairs are formed, both sexes may be observed lifting a wing, spreading the feathers to expose the speculum (the patch of bright color at the trailing edge of the wing), and placing the beak behind the raised wing as if preening. Then just before copulation, the male and female typically float face-to-face and pump their heads up and down.
