Behavior

Locomotion

Walking, Hopping, Climbing

Highly aquatic, awkward on land. Generally avoid walking; females will lead broods overland at least 1.2 km to water from upland nest sites or when moving between wetlands (McGilvrey 1966).

Flight

Take flight by running across water. Rapid, ceaseless wingbeats in flight, only glide when landing. Birds landing at high speed; with feet extended forward, “ski” across water surface to a stop.

Swimming And Diving

In contrast to dabbling ducks, swimming mergansers present a low profile. Well-adapted for diving with legs placed relatively far back under the body; birds propel themselves underwater using palmate feet and lobed hallux, while holding wings close to the body (Brooks 1945).

Self-Maintenance

Preening

Little information available. Birds remain on water or use dry sites such as rocks, floating logs, and river banks for comfort activities (LHF, M. L. Mallory pers. comm.).

Sleeping And Roosting

Gather at roost sites beginning at or shortly after sunset during fall and winter, arriving singly, in pairs, or small groups of < 20 (Barbour and DeGrange 1982, LHF). Roost sites in Missouri are typically located in scrub/shrub and flooded dead timber habitats (LHF). A Florida roost, used only by Hooded Mergansers, was on a pond 45 m in diameter located within a large pine-palmetto flatwoods. Fifty percent of the pond surface was covered with maidencane (Panicum hemitomon) and pickerel weed (Pontedaria lanceolata). The roost was used by 100 to 223 birds with an average of 175 birds in Jan (Barbour and DeGrange 1982).

Daily Time Budget

Little information available. Behavior and habitats used during breeding are difficult to sample and pre-breeding females are sensitive to disturbance; 35 h of time/activity budget data gathered on pre-breeding birds in Missouri found birds spent approximately 45% of their time foraging, 15% swimming, 17% resting, 16% preening, stretching and bathing, and 7% courting, being alert, or involved in aggressive interactions (LHF).

Agonistic Behavior

Male-male chasing commonly observed at 1 winter roost (Barbour and DeGrange 1982), but aggressive interactions between paired males comprised < 1% of the activities of pre-breeding birds in se. Missouri (LHF).

Spacing

Territoriality

No information available.

Dominance Hierarchies

No specific information, although information from other waterfowl species indicate paired birds are dominant over unpaired birds. Yearlings do not acquire definitive Alternate plumage until their second year and usually do not breed until this time; thus yearling birds are probably subordinate to older individuals.

Sexual Behavior

Mating System

Only monogamy reported.

Sex Ratio

Little known. In Missouri, day-old duckling sex ratio 55% males, 45% females, not significantly different from 1:1 (P > 0.10, n = 240 ducklings from 25 complete clutches; LHF). Only published estimate for adults is 1:1 at a winter roost in Florida (n = 175; Barbour and DeGrange 1982).

Courtship Displays

Courtship occurs in small groups consisting of at least one female and several males. No extensive information available on these behaviors in wild birds. Information and terminology for all displays and behaviors is summarized from Johnsgard (1961b, 1965) who made extensive observations on captive and some wild birds. He notes that in addition to their unique displays, Hooded Mergansers perform several courtship and copulatory displays similar to closely related Bucephala and Mergus .

Males have elaborate courtship behaviors which include Crest-raising, Head-shaking, Head-throws with Turn-the-back-of-the-head, Head-pumping, Upward-stretch, Upward-stretch with Wing-flap, and ritualized Drinking (Fig. 3). Crest-raising may occur separately or in conjunction with Head-shaking which together are often performed 3–4 times as a precursor to Head-throws. Head-throws, the most elaborate display, are usually performed with the male parallel to the intended female. With crest raised, males bring their head abruptly backward touching their back. A rolling frog-like crraaa-crrrooooo call is given as the head is returned to the upright position and turned away from the intended female. Sometimes after a Head-shake, no Head-throw is given, instead males extend their neck, open their bill and give a hollow pop call. Pumping involves an upward and outward motion of the head, with the bill tracing ellipses in space. Upward-stretch is a head shaking stretch performed with crest raised and appears to have evolved through ritualization of daily comfort movements. This behavior is sometimes accompanied with Wing-flaps. Drinking is a ritualized behavior that can be distinguished from normal drinking motions by the strongly depressed crest and almost vertical orientation of the bill.

Female courtship displays include Bobbing, where the head moves up and down in rapid, jerky motion with bill pointed downward, uttering a hoarse gack . More common is Head-pumping in response to the same behavior by males.

Copulation And Copulatory Displays

Copulation occurs on the water. Sequences begin with Drinking displays by both sexes as the male swims around the female with depressed crest. Following several repetitions of this display, a female solicits copulations by assuming a prone posture, holding her head just above and laying her tail flat on the water surface. The male immediately begins making jerky back and forth movements with his head, frequently followed by Drinking movements and commonly an Upward-stretch, with or without Wing-flapping. Abruptly, the male performs a Water-twitch (or Jab) by dipping his bill in the water while laterally shaking his head. This behavior is performed up to 8 times before the male suddenly stops, performs an Upward-stretch, with or without Wing-flaps, Preens-behind-the-wing on the side directed toward the female, and begins swimming in jerky movements toward the female. Rather than swim directly toward the female, males zigzag or tack, alternately presenting both sides of his erect crest. Once reaching the female, the male attempts to mount, raising his crest and Flicking-the-wing while treading. In 5 cases observed, the male successfully mounted twice. Mounting lasts at least 10 s with the male grasping the female’s nape.

Following copulation, the male slips off the female, retaining hold of her nape, and both birds rotate nearly a full turn. The male then releases the female and swims away in a straight line (“Steams”) in the Crest-raised posture for several meters. Males may or may not dive after Steaming. Both sexes bathe following copulation, females immediately after being released, males after steaming away from females.

Pair Bond Maintenance Displays

Pair bond maintenance seems to be associated with male Tail-cocking, Crest-depressed-and-directed-towards-female, and Post-humeral (tertial) Lifting Displays. Tail-cocking entails the male swimming ahead of the female with tail held at upward 45° angle. Crest-depressed-and-directed-toward-female Display is distinguished from a normal resting bird by the erect forehead feathers in contrast to the strongly depressed crest. Post-humeral Lifting is a subtle, often repeated lifting of the ornamental tertial feathers performed in conjunction with both displays above.

Duration Of Pair Bond

Pairs bonds seasonal; duration uncertain. Pairs have been observed in mid-Nov in se. Missouri; most birds migrating north through se. Missouri, beginning late Jan, are paired, but courting groups are not uncommon (LHF). Uncertain if courting birds are strictly migrants to northern areas or young birds. In all cases, males apparently abandon females immediately after females begin incubation.

Extra-Pair Copulations

No data available, but forced copulations known to occur in many waterfowl species.

Social And Interspecific Behavior

Degree Of Sociality

Most commonly observed in pairs or groups of < 40 individuals during migration and winter, unless at winter roosts. See Migration; also Behavior: self-maintenance/sleeping and roosting.

Play

No information.

NonprEdatory Interspecific Interactions

Generally avoids other species. May occupy winter roost sites with Wood Ducks. See Systematics: subspecies/related species, Breeding: nest site/nest site competition and brood parasitism.

Predation

Incubating females reported killed by raccoons (Procyon lotor), mink (Mustela vison), and black rat snakes (Elaphe obsoleta obsoleta; Bellrose 1976, Fendley 1980, LHF). Recorded egg predators include these same species plus black bear (Ursus minor), pine marten (Martes americanus), European Starling (Sturnus vulgaris), Northern Flicker (Colaptes auratus), and Red-headed and Red-bellied woodpecker (Melanerpes erythrocephalus, Melanerpes carolinus; Kennamer et al. 1988, Zicus 1990, D. K. McNicol and M. L. Mallory unpubl. data, LHF). Black rat snakes account for one-third of all depredated nests in se. Missouri (Hansen and Fredrickson 1990). Upon being disturbed at a nest as early as mid-incubation, at later incubation stages, or with ducklings females will perform Broken Wing Distraction Display (Mallory et al. 1998), propelling herself across the water with her wings in an attempt to lure the predator away, sometimes uttering a hoarse guttural gaaack.