ANATIDAE Ducks, Geese and Swans FAUNA PARAGUAY

ANATIDAE - DUCKS, GEESE AND SWANS

Twenty-one Paraguayan representative of this heterogeneous but instantly-recognisable family of aquatic and semi-aquatic birds. The use of the vernacular terms duck, goose and swan do not necessarily imply close relationships between the species involved. Globally the family can be split into three subfamilies (two in Paraguay): Anserinae is made up of four tribes (two represented in Paraguay), Anatinae consists of eight tribes (six of which occur in Paraguay) and the remaining subfamily Anseranatinae has a single representative confined to the Papuo-Australian region. See below for characteristics of the Paraguayan tribes.
Members of this family have robust, fully-scaled legs. The three front toes are linked with fleshy webs and the hallux is elevated and reduced. The neck is long and the bill in the great majority of species is blunt and spatulate. Bill is lined with serrated lamellae and the upper mandible has, at least temporarily, a horny tip known as a nail. In many species the bill is brightly-coloured. The plumage is thick and there is a well-developed, feathered oil gland. Salt glands are situated above each eye. The body is broad and elongated improving buoyancy, but makes locomotion on land difficult for many aquatic species and gives a characteristic shuffling or waddling gait. Wings are short, strong and pointed and most species re capable of rapid, powerful flight. Wing and chest muscles are pronounced and attach to a highly-keeled sternum which give a barrel-chested aspect. Brightly-coloured speculums are most developed in migratory species and like serve as a signal to maintain flock cohesion in flight. The flight feathers are moulted simultaneously after breeding, resulting in a period of flightlessness. Male ducks (sometimes known as drakes) possess a penis-like sexual organ. All Paraguayan species lay unspotted eggs in ground nests, lined with down feathers. The young are nidifugous and down-covered.

Subfamily Anserinae: Geese, Swans and Whistling-ducks

TRIBE DENDROCYGNINI "WHISTLING-DUCKS" - Three Paraguayan species in the genus Dendrocygna. Long-legged, long-necked, plump-bodied ducks that often perch in trees. Highly gregarious in behaviour though pairs apparently form for life. No sexual dimorphism and both sexes share incubation. Distinctive flight jizz, hump-backed, broad-winged and with drooping neck, the long legs protruding beyond the short tail. Shallow wing beats. Shrill whistling calls are often given in flight.

TRIBE ANSERINI "GEESE AND SWANS" - One Paraguayan species in the genus Coscoroba - an atypical goose-like swan. Long neck and mostly white plumage. Feed by up-ending. Highly gregarious in behaviour though pairs apparently form for life. No sexual dimorphism. Migratory, flying in V-formations.

Subfamily Anatinae: Ducks

TRIBE TADORNINI "SHELDGEESE" - One Paraguayan species in the genus Neochen. Goose-like with an erect stance. Long, thick neck and robust, square head. Broad-based, short bills and short legs. Feed on land by grazing. Male larger than the female.

TRIBE CAIRINI "PERCHING DUCKS" - Four quite different species in separate genera (Cairinia, Sarkidiornis, Amazonetta and Callonetta) forming an ill-defined group of uncertain affinities but linked by their tendency to perch in trees. Sexually dimorphic.

TRIBE ANATINI "DABBLING DUCKS" - Seven species in the genus Anas. Globally this is the largest genus of ducks. Sociable and often migratory species that feed by dabbling on the water surface, upending or grazing. Flight is fast and agile with an explosive take-off not requiring a run-up. They walk on land with a distinct waddle. Most species with a brightly-coloured speculum in the wing. Some species are sexually dimorphic.

TRIBE AYTHYINI "POCHARDS" - One Paraguayan species in the genus Netta, atypical in its tribe and closer to the dabbling ducks in behaviour than typical Pochards. Sleek, large-billed duck with a large, rounded head. Sexually dimorphic.

TRIBE MERGINI "SAWBILLS" - One Paraguayan species in the genus Mergus. A slender, long-billed duck with serrated, tooth-like cutting edges. Long, slender body, long neck and nuchal crest. Flight powerful, rapid and low over water.

TRIBE OXYURINI "STIFFTAILS" - Three Paraguayan species in three genera Oxyura, Nomonyx and the atypical Heteronetta. The former two species are diving ducks with long, stiffened tail feathers often held erect. The large feet are set well back on the body and they are clumsy on land. They fly with rapid beats of short, broad wings following a running take-off. Males of these species have bright blue bills and perform elaborate ritual displays to court females. Atypical Heteronetta is shaped more like a Dabbling Duck and swims with a low-set body. It is dull-coloured, secretive and the only duck species that is a nest parasite. Ducklings hatch quickly and are self-sufficient from the outset.

REFERENCES
Campbell B & Lack E 1985 - A Dictionary of Birds - T & AD Poyser.
Carbaneras C 1992 - Anatidae Handbook of the Birds of the World Volume 1 - Lynx Ediciones.
Madge S & Burn H 1992 - Wildfowl: An Identification Guide to the Ducks, Geese and Swans of the World - Helm.