Lake Duck

Characterized as one of the most distinctive diving waterfowl of the Southern Cone, this small-sized member of the Anatidae family features a total body length of 36 to 46 centimeters and an average weight ranging from 500 to 600 grams. It exhibits pronounced seasonal sexual dimorphism. During the breeding season, the adult male displays a striking nuptial plumage, showcasing a bright reddish-brown body that contrasts sharply with its jet-black head and neck. The most diagnostic feature of the breeding male is its intense powder-blue bill. In contrast, the female, as well as non-breeding males in eclipse plumage, is much more cryptically colored, presenting a mottled grayish-brown plumage characterized by two prominent pale horizontal stripes on the face (one running across the cheek below the eye and another along the throat line). Both sexes possess a rigid, spiny tail of dark feathers that is frequently held erect while floating. However, the most extraordinary anatomical feature of this taxon is internal: males possess an extraordinarily long, corkscrew-shaped phallus that can measure up to 42.5 centimeters when fully extended, which is longer than the bird´s actual body length, representing the longest phallus relative to body size of any vertebrate.

Geographical distribution: Native to and widely distributed across the southern regions of South America. Its primary range encompasses central and southern Chile (from the Coquimbo region down to Tierra del Fuego) and most of Argentina, extending eastward into Uruguay and the southernmost tip of Brazil (mainly within the state of Rio Grande do Sul). During the austral winter, northern populations may undertake short-distance migrations, reaching southern Paraguay, with accidental records documented as far south as the Falkland Islands.

Habitat: Closely associated with lentic freshwater and brackish aquatic environments. It strongly prefers shallow lakes, marshes, reservoirs, swamps, and slow-flowing rivers that feature a dense cover of emergent and floating vegetation along their margins, particularly bulrushes (Schoenoplectus) and cattails (Typha). It generally avoids deep open waters or fast-moving currents due to its specialized benthic foraging habits.

Feeding: Exhibits an omnivorous diet highly adapted to the benthos of limnic ecosystems. It obtains food primarily by diving in shallow waters, filtering the bottom sediment through its bill. It consumes seeds of aquatic plants, algae, and tender shoots, supplementing this plant matter with a diverse array of animal protein, including aquatic insect larvae (especially chironomids), small mollusks, crustaceans, and water snails.

Behavior: Highly aquatic and an exceptional diver, it is structurally adapted to swimming with its legs set far back on its body, which makes it extremely clumsy and vulnerable on land. It is a generally quiet and solitary species, often found in pairs, though it can form loose, small flocks during the non-breeding season. Males perform complex courtship displays that involve rhythmic head-shaking, splashing water forward with their bills, and emitting low-frequency acoustic hisses.

Nesting: The breeding season takes place between October and January. It constructs a well-concealed nest hidden deep within dense marsh vegetation, positioned just a few inches above the water level or floating semi-submerged while anchored to sturdy reeds. The nest is a semi-spherical cup constructed from dry stems and reed leaves, lined internally with a fine layer of soft down feathers. Females lay a clutch of 3 to 5 exceptionally large white or cream-colored eggs, which they incubate alone for a period of 23 to 25 days. Facultative brood parasitism has been occasionally observed in this species.

Conservation status: Currently classified under the status of Least Concern (LC) on the IUCN Red List of Threatened Species. Although its global population is considered stable and its geographical range is vast, localized populations face threats due to wetland loss and degradation driven by agricultural expansion, water pollution from chemical runoff, and the introduction of invasive predatory fish.