Stevens et al. (2005) described in detail the following behaviors for male and female Crested Duck (and compared them to those of other ducks):
Male displays include: Head-shake, head-flick, body-shake, backward-swim, double-grunt whistle, head-back/Tail-up + Turn head towards female, preen-behind-wing, prolonged dabble, bill-up call, chin-lift, chattering call, open-bill threat, and alarm calls.
Female displays: inciting, open-bill threat, decrescendo, low-swim, preen-behind-wing, prolonged dabble, threat calls.
Many of the displays of this species are conspicuous and striking, and females have loud calls. Male courtship displays have pronounced orientation components with respect to the target female. The long tail is often conspicuously raised, exposing the black undertail coverts, and the male’s crest is often erected during displays.
Two displays are unique to Lophonetta: the Backward-swim and the Bill-up Call. Backward-swim is a conspicuous display in the crested duck repertoire. Males frequently perform this movement during courting bouts, particularly in large mixed-sex groups. It appears to function to maintain broadside orientation to the courted female, and other displays may be given while the male swims in this unusual manner. The Bill-up Call and other displays incorporating an exaggerated vertical movement of the bill (Decrescendo, Head-shake) are also unique to this species. No species of Anas have been observed performing such exaggerated head movements (bill lifted 90 ̊ above horizontal) during vocalisations, nor do Anas females tend to perform exaggerated movements during Decrescendo calls in the manner of crested ducks.
Crested Ducks are notoriously non-gregarious and tend to be highly territorial. Flocks only develop in areas of unusually high food supplies, and in general, pairs will expel others of their own as well as alien species from their foraging areas (Johnsgard 1978).
This section is modified from Stevens et al. (2005).
Pre-copulatory Pumping: The head movements made during Pre-copulatory Pumping are very Anas-like (Johnsgard 1965).
Copulation: The male dabbled at the female’s back prior to mounting. The male wags his tail repeatedly after mounting the prone female, then moves the tail to the side (to right and left sides equally) for intromission and immediately dismounts. Duration of copulation, from mount to dismount, averages 8.25 s (± 2.63 s).
Post-copulatory Display: After copulation, the male dismounts and gives a Head-back/Tail-up display. On some occasions, he followed the display with Turn head towards female, then maintained the erect-neck, tail-up position while swimming in front of the female. The male’s head was turned to the side, as if to maintain position relative to the female. Unless disturbed by other birds, the male continues leading the female in this way for 14–17 s before returning to a normal swimming posture. The female alternates between bathing and Inciting as she follows the male during this display.
Social and interspecific behavior
Crested Ducks are markedly aggressive towards own species and many other bird species when breeding. In intraspecific disputes, male and female may chase whichever member of another family is closest. Pairs nesting on plateau lakes in Patagonia Argentina have been observed chasing large waterfowl such as Flying Steamer-Duck (Tachyeres patachonicus) and Upland Goose (Chloephaga picta) (Buitron and Nuechterlein 1989).
Likely predators include Chloephaga geese, steamer-ducks (Tachyeres spp.), Peregrine Falcon (Falco peregrinus), Aplomado Falcon (Falco femoralis), and Kelp Gull (Larus dominicanus), among others.