According to BOW:
Intraspecific aggression (threatening posture, rushing, chasing, biting, bill grabbing, pushing, and pursuit flights) is a common component of courtship, pair formation, and territorial defense. Most aggressive encounters on the wintering grounds, during migration, and early in breeding season occur during courtship and pair formation between conspecifics (Wishart 1983b). In coastal N. Carolina during winter, 87% of aggressive interactions are between conspecifics (n = 99): 51.1% male:male; 22.0% male:female; 11.6% female:female; and 15.1% female:male; males dominant to females when pair status identical; paired females dominant over unpaired males (n = 86; Hepp and Hair 1984).
Birds wintering on the Yucatan Peninsula, Mexico, spent <1.0% of day in aggressive behavior; 86.0% of all aggressive encounters are intraspecific (n = 143); supplant (one individual moves into an area and other moves out without confrontation) 7.8%; threat (performed with body low, tail straight, head and neck stretched low and parallel to water with the bill open) 74.5%; chase (one bird rushing another, often nipping it on the tail, causing it to move rapidly away) 16.7%; and fight (grabbing feathers with bill, pecking, and beating with wings) 1.0% (Thompson and Baldassarre Thompson and Baldassarre 1991, Thompson and Baldassarre 1992).
Jump-flights (male making short flight from one side of group of courting males to the other; see Sexual behavior: courtship displays) and pursuit flights reported for birds wintering on southern high plains of Texas (Soutiere et al. 1972); group flights, often associated with social displays, observed throughout winter in British Columbia and early Apr in Saskatchewan (Wishart 1983b).
Paired males do not tolerate conspecifics on or flying close over their breeding territories. Territorial defense is primarily by group flights: flight initiated when resident male rapidly swims toward and flushes trespasser from territory, engaging it in flight and physically attacking it in the air by biting at its tail. Group flights sometimes preceded by bouts of ritualized Tandem-swimming: both males swim rapidly with heads erect, aggressor close behind the trespasser, pecking at its tail, lunging at it or occasionally beating it with its wings. On breeding grounds in Saskatchewan, most common mid-Apr to early Jun (Wishart 1983b).
Interspecific aggression between American Wigeon and other species reported on wintering grounds, breeding grounds, and during migration. During migration in mixed flocks of waterfowl and American Coots, 4.0% (n = 51) of interactions between American Wigeon and American Coots were aggressive (Eddleman et al. 1985b). In Yucatan, Mexico, 14.0% (n = 143) of aggressive interactions involving American Wigeon interspecific; Northern Shoveler, 12.6%; Blue-winged Teal, 1.4% (Thompson and Baldassarre 1992).
In Saskatchewan (Wishart 1983b), 84.0% (n = 666) of all interspecific interactions observed among waterbirds involved American Wigeon which, according to their abundance, interacted less than expected with Mallard, Lesser Scaup, and Northern Shoveler; more than expected with Blue-winged Teal, Gadwall, and American Coot; and at expected levels with Northern Pintail. Dominated all species it interacted with except Mallard, Canvasback, and American Coot; aggressive behaviors included chase, fights, and pursuit flights.
From Wishart 1983b. On arrival at breeding grounds, pair members remain closely associated while in flocks; other conspecifics not tolerated closer than 2–3 m without aggression. Male communicative interactions include threats and rushes; female interactions involve Chin-lifting and Inciting behaviors. Threatening component of Inciting behavior consists of a posture with head lowered, neck stretched forward, bill open and head repeatedly drawn back and thrust up and out while uttering Inciting Call. In a modified version, the head is stretched back instead of forward. Over-the-shoulder Inciting is performed by females threatened by courting males that follow (this behavior observed on land and during pursuit flights). Chin-lifting behavior involves the head drawn back and upward repeatedly, and is directed toward favored male between bouts of threatening other males.
In Saskatchewan in early spring, pairs form small flocks that move widely over the breeding area; home range size averages 25.3 ha; mid-May pairs disassociate from conspecifics and establish territories. Territories during pre-laying consist of 1–3 potholes and surrounding uplands and average 7.8 ha ± 4.8 SD (n = 6; Wishart 1983b). Most wetlands and adjacent uplands are used exclusively by one pair; if a pothole is used by >1 pair, each is restricted to its part of water surface but both pairs use adjacent areas. There is sequential use of some territories by different pairs.
Tend to be spaced out, a single pair to a marsh-bordered pond; actively defend pond surface and adjacent nesting area; may defend loafing and feeding areas in adjacent uplands. Prior to establishment of territories and breeding, aggression occurs among pairs coming closer than 2–3 m (Wishart 1983b).
Pair formation begins before arrival on wintering grounds. Skewed sex ratio (see Demography) makes competition for mates on the wintering grounds intense; males compete for females through overt aggression and ritualized displays that highlight their plumage patterns (see Courtship displays). At height of courtship a mass chase of a female occurs with males attempting to grab or mount the female; female responds either by diving or by taking flight; if female flushes, courting males follow and a rapid group flight ensues. On landing, chasing and courtship resume until either a pair is formed or the group disbands. Although some early male:female associations are ephemeral, bonds generally persist and strengthen through the winter; birds pairing early have an opportunity to test the quality of a mate. In Texas, complete copulation sequences have been observed in paired birds. Such copulations, including mutual pre- and postcopulatory displays by the male and female, may be a test of mate quality and serve to strengthen the pair bond. Dominant males that had completed prealternate molt pair more successfully (Johnsgard 1960d, Wishart Wishart 1983b, Wishart 1983a, Wishart 1985). Male qualities (persistence, aggressiveness, and flying abilities) in winter courtship are the same qualities required for successful defense of a breeding territory. Concurrently, courtship flights and attempts at copulation during courtship test a female's ability to avoid aggressive males. Courtship behavior accounts for <1% of activity in fall and winter, and does not differ among months (Hepp and Hair 1983, Turnbull and Baldassarre 1987, Thompson and Baldassarre 1991).
By arrival in mid-Apr at Moose Jaw, Saskatchewan, all females are paired, including first year birds. Most pairs show a persistent pair bond, males accompanying their females closely and defending them when approached or harassed by other males. While on the water, female swims ahead with male following within 0.2–1.5 m in alert posture. Male also follows closely when walking through nesting cover or while feeding in stubble fields. When a female is at the nest, the paired male spends a large portion of his time alert on the water, intolerant of conspecifics entering the territory; when separated, the male vocalizes continuously.
As incubation progresses, the stability of the pair bond weakens and the male spends less time on territory. In Idaho, males abandon females by day 8 of incubation, (17 d after onset of egg-laying; n = 5; Oring 1964a); in Saskatchewan, males abandon females on average by 25 Jun, 26.6 d after the onset of egg-laying (n = 7; Wishart 1983b). Occasionally males are observed tending broods (Mcclanahan 1942; Wishart 1983b).
Pair bond dissolution occurs once the female is no longer fertile or vulnerable to predators. By dissolving the pair bond at this point the female increases her investment in parental care, and the male increases his fitness by undergoing molt and beginning competition for a new mate for the ensuing year (Wishart 1983b).
Courtship displays follow Wishart (Wishart 1983b, Wishart 1983a) except where noted (see Figure 3).
Swimming-Shake. A ritualized form of the Swimming-Shake is performed by American Wigeon as a comfort movement, and by many dabbling duck species as a preamble to a sequence of other displays (e.g., Introductory-shake). In American Wigeon it is a major display with no introductory function. It is preceded by rapid Tail-wagging; prior to completion of Tail-wagging the head and neck are thrust forward and upward. As the anterior portion of the breast is elevated out of the water, the head and neck further extended up and forward, and several rapid body shakes and head rotations are performed. As shakes end, the neck is pulled into the body and the breast lowered forward onto the water; neck and bill are then tucked into the breast with crown erect; this display terminated with another rapid Tail-wagging. Full display including Tail-wags averages 3.5 s ± 0.87 SD (n = 19). Display most often performed within 1 m of the female (70.2%) while the male is aligned parallel to her (62.5%; n = 104). Shaking movements accentuate the black-and-white bands on the rump, and the colorful bill and head markings, and function to draw the attention of the female to the adult male in full alternate plumage.
Bathe and Wing-Flap. Although commonly performed by American Wigeon as a comfort movement, this behavior apparently has a secondary function in courtship, as it is generally performed immediately after aggressive encounters while courting, by males parallel to (60%) and within 1 m of female (76%; n = 25). Bathing consists of a series of 2–6 head-dippings accompanied by rapid wing-shuffling. Bouts average 6.08 s ± 2.70 SD (n = 10); 96.4% (n = 28) of bathing bouts are followed by Wing-flap. Wing-flap requires 2.16 s ± 0.57 SD (n = 31) and the number of wing beats in sequence average 5.3 ± 1.5 SD (n = 23); this is occasionally followed by pronounced Tail-wagging. This behavior draws attention to the performer both visually and acoustically; while wings are open, the white upperwing-patch denoting age is visible (Wishart 1981); rearing out of the water and opening the wings increases the apparent size of an individual and may assist in establishing dominance.
Burp. Performed by the male by stretching the head and neck up in an alert posture, erecting the crown feathers, opening the bill, and emitting a Slow Whistle vocalization (see Vocalizations: vocal array); 90.9% are given within 1.3 m of female, 9.1% within 1.3–2.3 m (n = 143). Performed ahead of, beside, and behind the female; often repeated 2–3 times by a courting individual and 75.2% (n = 143) are given concurrently by other males in group. The Burp is performed in the context of other behaviors, such as: Head-shake, Wings-up, Wing-flap, Swimming-shake, Tail-wagging, and/or Bathe. By accentuating the striking head and bill colors of the mature male, the Burp appears to be primarily an attention-getting display performed to influence female behavior.
Turn-Back-of-Head. Previously described by Johnsgard (Johnsgard 1965) for male Eurasian Wigeon as a means of leading the female away from other courting males, this behavior is often performed by American Wigeon males. During this display the male swims alertly ahead of the female with his head tilted to one side observing her movements, as well as those of other males, while advertising his own striking head plumage. While following, female frequently performs Inciting and Chin-lifting over shoulder at other males. If the female does not follow, or is impeded by other males, the male ends the display and aggression may occur between the males.
Jump-Flight. Described by Soutiere et al. (Soutiere et al. 1972) for American Wigeon, this behavior is similar to that described for Mallard and Northern Shoveler. Performed by the male on the water left behind by a courtship group: male flies up and over group, landing ahead of a swimming female so that it may perform Turn-back-of-head Display. Flight is short, 3–5 m, and lacking any ritualized posturing; functions to attract attention of female. Males performing Jump-flights usually elicit Inciting behavior from a female and aggressive threats from other males; frequently ends in a courtship flight.
Facing. Common display performed mutually by both sexes during courtship but usually initiated by the male. Described by Johnsgard (Johnsgard 1965) and others for Eurasian Wigeon as resembling the Triumph Ceremony of geese. In the American Wigeon, often follows Turn-back-of-head when the female does not follow or is prevented from doing so by other courting males. The performing male swims back to the female and faces her alertly breast-to-breast; from this position he attempts to herd her away from other suitors.
This strongly directional display seems to be a direct assertion of a male's choice of mate. The female frequently performs Chin-lifting and Inciting movements at other males from this position, but the male does not perform Chin-lift as described by Johnsgard (Johnsgard 1965) for Eurasian Wigeon. However, he often performs Head-shake and Bill-dip and regularly rotates around quickly to threaten or make aggressive attacks on other males. This activity usually ends with a bout of preening or with the male resuming Turn-back-of head and leading the female away.
Wings-Up. One of most frequently performed displays by males during courtship in winter. Wings are arched over the back with primaries crossed; degree of arching is related to the intensity of the display, as is the rapidity of Tail-wagging that often occurs concurrently. Usually during this display the head is held out and compressed back against the neck and Fast Whistle is given repeatedly.
The display usually occurs in an aggressive context during the most vigorous stages of social courtship. It is usually given when a male is within 0.5 m of a female while side-on to her field of vision; occasionally given as a male is Facing, prior to swimming aggressively at other males; aggressive chases often lead to a female flushing into a courtship-pursuit-flight. Wings-up is also observed on breeding grounds where it is generally performed quickly prior to chase or fight.
Once territories are established, Wings-up is given only briefly by paired males when they trespass onto a territory and are threatened by a resident male prior to pursuit flight. Later in spring, territorial males also perform this display when lone males trespass; often followed by a bout of Tandem-swimming and then a pursuit flight between the two males. In performing this aggressive courtship display, the male dramatically increases his apparent body size, which assists in establishing dominance over other males. With wings raised, the white upperwing-patch, indicative of age (Wishart 1981), is displayed; and Tail-wagging draws attention to the black-and-white rump bands indicative of stage of molt.
Copulation And Copulatory Displays
Precopulatory Head-pumping -- in which the head is held alertly, then elevated by stretching the neck up slowly, with a short pause, and then a more rapid lowering by retracting the neck -- precedes copulation of birds of known breeding status. This is performed while birds are either swimming or stationary on the water. It is usually given by both members of a pair and is generally of short duration (mean = 4.7 s ± 3.2 SD; n = 9); most frequently initiated by female.
In copulations preceded by Head-pumping, the female stops Head-pumping and assumes a Prone position prior to a deliberate, but slow mount from the side by the male, while grasping the female's nape in his bill. Once mounted, the male continues Head-pumping, forcing the female's head up and down in water and causing her to elevate her tail. The male spends an average of 23.4 s ± 12.4 SD (n = 22) on top of the female.
Following copulation the male dismounts and generally assumes an Alert position (93% of the time), and the female performs Wing-flap and Bathe 96% of the time (n = 27). Preening and Scratching are also primary post-copulatory activities of females while Facing and Slow Whistle vocalizations are common postcopulatory activities of males (Wishart 1983b).
Extra-Pair Mating Behavior
Forced copulation occurs occasionally early in breeding season; generally either without Precopulatory Head-pumping or with Head-pumping initiated by male; typical response of female is to move into cover and hide. Infrequent during late laying and incubation (Wishart 1983b).
Social and Interspecific Behavior
Degree Of Sociality
Often congregates in large flocks on fall/wintering grounds, especially for feeding. During the breeding season, found typically in small groups, pairs, or individuals. During fall and spring migrations, generally travels in small, single-species flocks (2–10), or mingles in small flocks with Gadwalls, Mallards, American Coots, and various diving ducks. Postbreeding males, during molt migration, congregate in flocks of various sizes with both dabbling and diving ducks, and American Coots; flocks are often large (>1,000; Wishart 1983b, Eddleman et al. 1985b). Upon arrival on breeding grounds in s.-central Saskatchewan in mid-Apr, individuals remain in small groups of 2–15 pairs and lone (unpaired) males until territories are established; pairs remain closely associated while in flocks and other conspecifics are not tolerated closer than 2–3 m. By prelaying, territories are well established, and individuals very intolerant of trespassers; 100% of pairs were disassociated from conspecifics by 21 May–14 Jun at Moose Jaw, Saskatchewan (n = 48; Wishart 1983b).
No play activities observed.
Nonpredatory Interspecific Interactions
See Agonistic Behavior: physical interactions. Occurs in mixed flocks on open water. Feeds on plant matter churned up by American Coots, Gadwalls, Canvasbacks, Lesser Scaup, Northern Pintails, Redheads, Brant, and swans; occasionally robs food from American Coots (see Food Habits: feeding; food capture and consumption). Spatial overlap and commensal feeding between American Wigeon and American Coot increases through fall into winter as sources of preferred foods become less accessible and/or available (Eddleman et al. 1985b)."