Tachyeres brachypterus

The Flightless Steamer Duck is a large, robust bird, with adult males typically weighing up to 6 kilograms. Adult plumage is characterized by a grayish body, with lighter underparts, and a distinctly white eye-ring and cheek patch that stand out against the darker head. Females are slightly smaller and have a more muted coloration, often with a brownish hue. Juveniles resemble females but are more uniformly brown with less distinct markings. In terms of field marks, this species is unmistakable due to its sheer size and flightless nature. Unlike other ducks that may take to the air when disturbed, the Flightless Steamer Duck remains on the water, where it demonstrates its 'steaming' behavior. This bird's silhouette is bulky, with a long neck and a heavy body that sits low in the water. When perching, it often assumes a relaxed posture on rocks or shores, with its body aligned horizontally. Despite their unique adaptations, these ducks can be confused with the Flying Steamer Duck (Tachyeres patachonicus), although the latter is capable of flight and generally displays a more streamlined form.

The Flightless Steamer Duck's diet is primarily composed of marine invertebrates. Mollusks, such as mussels and clams, are staple food items, which the duck expertly pries open with its powerful bill. Crustaceans, including crabs and shrimp, supplement its diet, particularly during the warmer months when these prey items are more abundant. The duck forages by diving, often to substantial depths, using both its wings and feet to maneuver underwater. It typically feeds during daylight hours, although peak feeding activity often occurs during early morning and late afternoon when tides are favorable in exposing or submerging coastal food resources. Seasonal variations in diet are relatively minimal, given the bird's consistent coastal habitat, though shifts in prey type abundance can influence specific dietary patterns.

Socially, the Flightless Steamer Duck exhibits a largely solitary or paired lifestyle, particularly during the breeding season when pairs aggressively defend territorial boundaries. The courtship displays of this species involve elaborate head movements and vocalizations, with males often seen chasing rival suitors away from their territory. Outside of breeding, these ducks may form small, loose groups, although their inherently aggressive nature often leads to skirmishes even in non-breeding contexts. When faced with predators, such as gulls or skuas, the ducks exhibit defensive behaviors that include loud vocalizations and group mobbing if in company. Daily activity patterns see the ducks resting during midday, with increased activity in morning and evening. Despite their flightlessness, they remain vigilant, using both visual and auditory cues to detect threats.

Nesting for the Flightless Steamer Duck occurs in secluded coastal locations. Nests are typically constructed on sheltered rocky islets or in dense vegetation near the shoreline. The nest itself is a simple scrape lined with feathers and down. Clutch size generally ranges from 5 to 9 eggs, with incubation performed solely by the female over a period of about 30 to 40 days. Once hatched, the ducklings are precocial, leaving the nest shortly after to follow the mother to water, where they begin foraging under her watchful eye. Both parents play roles in defending the young from predators, though the female assumes the primary role in caring for the ducklings. Typically, only one brood is raised per year, though occasionally, a second clutch may be laid if the first is lost early in the season.

The primary vocalization of the Flightless Steamer Duck is a harsh, grating call that serves both as a territorial marker and an alarm signal. This call is typically a series of rapid, throaty notes that can carry across long distances. During courtship, males produce softer, more rhythmic quacking sounds that contrast with their usual harsh vocalizations. Alarm calls are sharper and more urgent, often prompting a defensive response from nearby ducks. While not known for a melodic dawn chorus, the species is nonetheless vocal throughout the day, especially during breeding and territory disputes.

• 1The Flightless Steamer Duck weighs up to 6 kg, making it one of the heaviest ducks that cannot fly.
• 2Their name comes from their unique way of using wings and feet to 'steam' across the water.
• 3Despite their flightlessness, these ducks are exceptionally strong swimmers and divers.
• 4The Flightless Steamer Duck can fend off predators with powerful wing beats and aggressive behavior.
• 5They are one of only four species in the genus Tachyeres, three of which are flightless.
• 6Steamer Ducks are known to engage in fierce territorial battles, often resulting in injury or death.
• 7These ducks are an excellent example of island gigantism, a phenomenon where species evolve larger sizes on islands.

Currently, the IUCN lists the Flightless Steamer Duck as Least Concern, though its population trends warrant monitoring due to potential threats from human activity, particularly fishing and coastal development. The species has historically maintained stable populations, but localized threats such as oil spills, pollution, and habitat disturbance pose significant risks. Conservation efforts focus on habitat protection and monitoring population health. Being a regionally confined species, the Flightless Steamer Duck serves as an indicator of the ecological health of the southern South American coastal ecosystems.