Anatidaeducks, geese, and swans

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Anatidae comprises 49 genera in 5 subfamilies: Anatinae, Anserinae, Dendrocygninae, Stictonettinae, and Tadorninae. The largest subfamily, Anatinae, includes eight groups: Tadornini (shelducks and allies: five genera, 14 species); Tachyerini (steamer ducks: one genus, four species); Cairini (perching ducks and allies: nine genera, 13 species); Merganettini (Torrent Duck (Merganetta armata)); Anatini (dabbling ducks: four genera, 40 species); Aythyini (pochards: two genera, 15 species); Mergini (mergansers and allies: seven genera, 18 species); and Oxyurini (stifftails: 3 genera, eight species).

Anatids are distributed worldwide, except for the Antarctic region.

Anatids inhabit aquatic habitats such as lakes, ponds, streams, rivers and marshes. Some taxa inhabit marine environments outside of the breeding season.

Eggs are incubated for 22-40 days and hatching is synchronous within 24 hours. Several days prior to hatching young chicks start calling from inside the egg. Chicks are precocial (nidifugous), born with down and eyes open. Chicks can walk and swim within hours of hatching. Chicks forage for themselves while staying in close proximity of the mother. Fledging occurs at 5-10 weeks. In some species young of the year will return to the breeding grounds with parents for one or two years. Adult plumage acquisition may take one to three years. Most ducks are sexually mature at one or two years of age, whereas geese and swans may mature at five years. Life expectancy in the wild for individuals surviving their first year may be one or two additional years for ducks and four or more for geese and swans.

Anatids are medium to large birds (30-180 cm; 230 g -22.5 kg). The plumage of Anseranatinae and Anserinae taxa is generally sexually monomorphic, whereas Anatinae plumage is sexually dimorphic. Plumage varies from brown, gray or white, to black and white combinations. Some anatid males and some females may have a brightly colored speculum (patch of color on the secondaries) in metallic green, bronze or blue. Juvenile plumage is duller, but often similar to adult plumage. The neck is relatively long and the head is small. Wings are short and well -developed wing muscles insert on a deeply keeled sternum. The tail may be short and rounded or longer and narrow. The bill is broad with lamellate interior in many species. In some taxa the bill has a conspicuous horny or fleshy knob-like projection. Male bill color may be bright color at onset of breeding season. The palate is desmognathous. All species have salt glands above the eye. Legs are set far back on the body, the front three toes are webbed and the hallux is either absent or small and elevated. Male copulatory organ is present. Males also have partly or completely ossified tracheal and syringeal bullae. Oil gland is feathered.

Some anatids may breed alongside conspecifics, congeners or other bird species such as Peregrine Falcons (Falco peregrinus) or Rough-legged Buzzards (Buteo lagopus).

Anatidae taxa are herbivorous, although may also forage for aquatic invertebrates. Many anatids eat the seeds, roots, stems, leaves and flowers of aquatic vegetation. Some taxa feed on plankton or algae. Other food items taken include: mollusks, aquatic insects, crustaceans and small fish.

Mammalian predators of anatids include: humans, red fox (Vulpes vulpes), striped skunk (Mephitis mephitis), raccoon (Procyon lotor), badger (Taxidea taxus), coyote (Canis latrans), weasels and minks. Avian predators include: American Crow (Corvus brachyrhynchos), Black-billed Magpie (Pica pica), skuas(Catharacta), and owls

Most species of anatids are considered seasonally monogamous, although multiple partner copulations within a breeding season may occur in some species. Some anatids are polygynous. Mates may change from year to year in some species, or may be maintained for multiple years in other species. Pair formation often begins during the nonbreeding season. Courtship displays include head and wing movements, vocalizations and swimming patterns. Almost all species copulate on the water. In most species, the female constructs the nest while the male defends the feeding territory and guards the female as she forages.

Some anatids are aggressively territorial while others are colonial nesters. Colonies are generally small in size ranging from several dozen to over a hundred pairs. Anatids breed seasonally although some species maintain territories year round. Nest sites vary from shallow scrapes on land, mounds of plant material on land or water, to nest holes in trees. Nesting material includes vegetation and feathers. Clutch size ranges from 4-13 eggs with an egg-laying interval of 24 hours. Females of some species will deposit eggs in other female's nests. Some species are parasitic and will lay eggs in other species' nests.

In most species females begin incubation after the last egg has been laid and continue to incubate for 22-40 days. Males generally do not incubate, but will guard the female and defend the territory. Females may cover eggs with down when they leave the nest. After hatching, the female leads chicks on foraging forays, sometimes pointing out food items and always guarding the young. Males will sometimes accompany the young and provide predator protection. Generally females guard chicks until they fledge at about five to ten weeks.

Many anatids are migratory, although tropical and subtropical species remain close to breeding grounds during non-breeding season. Anatids are known for their flock formations, which may serve to provide predator protection or to facilitate locating abundant food sources. Anatids may form mixed or monotypic flocks. Anatids spend copious amounts of time in the water and spend a great deal of time on preening and feather maintenance. They use their bills to coat (and waterproof) their feathers with oil from the uropygial gland. Some taxa may be forage or conduct courtship displays at night and may be seen roosting during the day. Anatids often form small groups to roost either on the water or on land. When on the water, a sleeping bird will tuck its bill under its wing; on land birds may stand on one leg.

Anatids may form small flocks or groups of up to several hundred thousand individuals. Anatids appear socially active while feeding, roosting, and migrating. Pair formation and courtship displays frequently occur in groups. Flock formation occurs predominantly outside the breeding season, although some species are colonial breeders. And some species retain cohesive family groups year round.

Anatids vocalize markedly during the breeding season, as many vocalizations are integral to courtship, territoriality and brood care. Most species exhibit sexual variation in vocalizations with male vocalizations often more high-pitched than female vocalizations. In general, vocalizations are varied and include: trumpeting, whistles, twitters, honks, barks, grunts, quacks, croaks and growls.

Humans exploit anatids extensively. Anatids are hunted for sport and for subsistence. Many species have been domesticated for egg, meat and liver production. Eiders are raised for down (feathers) which is noted for its excellent insulating properties and is used in comforters, mattresses, pillows, and sleeping bags. Some anatids are used as 'watchdogs' as the birds are alert and provide loud alarm calls when disturbed, thereby providing property protection.

When foraging in large flocks, some anatids can cause damage to agricultural crops including: potatoes, carrots, and winter wheat and barely.

Thirty-eight anatid taxa are listed in the IUCN Red List of Threatened Species. Five taxa are listed as 'Extinct' (Alopochen mauritianus, Anas marecula, A. theodori, Camptorhynchus labradorius, Mergus australis). Five taxa are listed as 'Critically Endangered' (Anas nesiotis, Aythya innotata, Mergus octosetaceus, Rhodonessa caryophyllacea, Tadorna cristata). Other anatids include seven listed as 'Endangered', 14 as 'Vulnerable', and seven as 'Lower Risk'. Major threats include: introduced species, human hunting and collection, habitat destruction (drainage of wetlands) and agrochemical use.

The evolutionary relationships of Anatidae are vigorously debated. Generally, Anatidae is considered sister to Anhimidae (screamers) and taken together these groups form Anseriformes. Within Anatidae the monophyly of subfamilies and tribes are strongly contested. Morphological and behavioral evidence supports three subfamily divisions (Anseranatinae, Anserinae, Anatinae) within Anatidea. Anseranatinae (Magpie Goose) is hypothesized as most basal within Anatidae, and sister to the group comprising Anserinae (swans and geese) and Anatinae (ducks). Within Anserinae monophyly of the tribe Dendrocygnini is questioned. Differing hypotheses of relationships suggest the White-backed Duck (Thalassornis leuconotus) as sister to whistling ducks (Dendrocygnini), or as sister to stifftails (Oxyurini), or supports recognition of the species as a monospecific tribe (Thalassorini) or subfamily (Thalassorinae). The Cape Barren Goose (Cereopsis novaehollandiae) is commonly recognized as the sole species within tribe Cereopsini, although there remains support for its inclusion within Tadorini or Anserini. Within Anatinae, the composition of tribes Tadorini and Cairini have also been frequently revised. Traditional hierarchies included steamer ducks and Torrent Duck (Merganetta armata) within tribe Tadorini, although current evidence suggests steamer ducks be recognized as tribe Tachyerini with tribe Merganettini comprising the single species of Torrent Duck. Tribe Cairini has been described as a heterogeneous group arguably united due to similarities in behavior and breeding biology.

The oldest anatid remains may be wing fragments of Eonessa from Eocene deposits in North America. Ramainvillia and Cygnopterus fossils have been dated from the early Oligocene in France and Belguim. From France, Anas blanchardi has been dated to the Miocene, and Dendrochen and Mergus are known from the early and middle Miocene respectively. Tadorna fossils have been recovered from the middle Miocene in Germany and the Pleistocene in North America. Paranyroca magna dates from early Miocene of South Dakota. In North America, anatid fossils are common in freshwater deposits of the Pliocene and Pleistocene.

Campbell, B., and E. Lack, editors. 1985. A Dictionary of Birds. Buteo Books, Vermillion, SD.

del Hoyo, J., Elliott, A. & Sargatal, J. (eds.) 1992. Handbood of the Birds of the World. Vol. 1. Lynx Edicions, Barcelona.

Ericson Per G P. 1997. Systematic relationships of the palaeogene family Presbyornithidae (Aves: Anseriformes). Zoological Journal of the Linnean Society. 121(4). 429-483.

Feduccia, A. 1999. The Origin and Evolution of Birds, 2nd edition. Yale University Press New Haven.

Livezey Bradley C. 1997. A phylogenetic analysis of basal Anseriformes, the fossil Presbyornis, and the interordinal relationships of waterfowl. Zoological Journal of the Linnean Society. 121(4). 361-428.

Sibley, C. G. & J. E. Ahlquist. 1990. Phylogeny and Classification of Birds, A Study in Molecular Evolution. Yale Univ. Press.

Contributors

Laura Howard (author), Animal Diversity Web.

Glossary

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate

visual

uses sight to communicate