Like most members of the Anatidae family, long-tailed ducks are socially monogamous. Long-tailed ducks may breed in single pairs or loose groups. Breeding pairs can form as early as individuals reach the breeding grounds. Pairs can re-form for several years or individuals may select new mates each mating season. Breeding may be initiated before spring breeding plumage develops, but in most cases, breeding occurs after.
Long-tailed ducks engage in an elaborate courtship process, though sexual selection has only been studied superficially. Males will approach available females with an upright tail and bill held outwards, a few inches from the surface of the water. When closer to his potential mate, the male will bow and then pull his head back with his bill held upward. As he is lowering his head, he will emit calls. A series of four or five calls with deep notes have been observed. These calls often attract other males and they often physically fight and chase each other for the available female. Females call in response to initial calls from the males and hold their head close to their body to indicate availability. Females will then lead males to a mating location.
Mating System: monogamous
Breeding can begin as early as May, but varies depending on the location of the breeding ground and the presence of mates. Long-tailed ducks can begin mating as early as their second year after birth. They mate near open water, either freshwater or marine, and try to nest on dry ground hidden among rocks or under plant growth. Nests are bowl-shaped and constructed by the female. They consist of nearby grasses and females pluck down from their own bodies to line the nest.
Females usually lay 6 to 8 eggs: on average, laying one egg per day. Clutch sizes of up to 17 have been recorded, but this is likely the result brood parasitism as some females will lay eggs in other's nests. Females will raise one brood per season, but can lay eggs several times if unsuccessful. Since fall migration occurs relatively late, long-tailed ducks have a long breeding season and can attempt raising a brood several times. Once eggs are laid, the incubation period lasts from 24 to 30 days. Young ducklings remain in the nest until they fledge after 35 to 40 days. The fledglings form groups of 3 to 4 broods that are tended by older females.
Breeding interval: Long-tailed ducks breed once yearly.
Breeding season: Breeding usually occurs between May and July.
Range eggs per season: 5 to 11.
Range time to hatching: 24 to 30 days.
Range fledging age: 35 to 40 days.
Range age at sexual or reproductive maturity (female): 2 (high) years.
Range age at sexual or reproductive maturity (male): 2 (high) years.
Key Reproductive Features: seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate)
While eggs are being laid, the male will reside in the open water and help defend the nest. During the incubation period between late June and early September, the male will leave and begin molting. The newly laid eggs are then incubated and defended by the female for 24 to 30 days. Although newly hatched young can feed themselves, they are fed and closely tended by their mother. When the young begin walking, the mother leads her brood over to the water and teaches them to dive for food. First flight can occur anywhere between 35 to 40 days old. Anywhere between August and October, the mothers will leave their young to molt and ducklings will gather into large groups in and around the water. These groups are often tended by slightly older females.
According to a study of body mass dynamics in adult females during incubation, females lose proportionately less mass and rely less on endogenous reserves to lay and incubate eggs than other diving ducks. Specifically, females lose approximately 7% of their mass during incubation: average weight is 618 g at clutch completion and then drops down to 575 g at hatching. Because females are relatively smaller than other waterfowl breeding in the tundra and have access to high-quality nutrients, long-tailed ducks are able to maintain high nesting attendance rates and constant incubation without losing too much of their endogenous reserves.
Parental Investment: precocial ; female parental care ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Male, Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Provisioning: Female, Protecting: Female)