Anseriformesducks, geese, swans, and relatives

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Anseriformes comprises three families, Anhimidae (screamers), Anatidae (geese, swans and ducks), and Anseranatidae (magpie goose), with 48 genera and 161 species.

Anseriform taxa are distributed worldwide, except for the Antarctic region. Anhimids are restricted to South America and magpie geese (Anseranatidae) are found in Australia and New Guinea.

Anseriform birds inhabit aquatic environments including lakes, ponds, streams, rivers, swamps and marshes. Some taxa are found in marine environments outside of the breeding season.

Anseriform incubation lasts from 22-47 days. Young are precocial, hatching with down and eyes open. Young generally forage for themselves shortly after hatching. Fledging occurs at about 5-10 weeks. Age at first reproduction varies with species, ranging from one to five years of age.

Anseriform birds are medium to large birds (30-180 cm; 230 g -22.5 kg). The plumage varies from gray or brown to black and white. Screamers are noted for head and neck ornaments, while anatids may have brightly colored speculums (patch of color on secondaries) in green, bronze, or blue. Juveniles have similar, yet duller plumage. In anhimids the bill is short and hooked, while anatid bills are broad and rounded. Most species have lamellate interior (reduced in anhimids). The palate is desmognathous. Front toes are webbed, with long non-elevated hallux (ahimids), or absent or small and elevated (anatids). Male anatids have copulatory organ and partly or completely ossified tracheal and syringeal bullae. Anhimids lack uncinate processes on ribs and have pneumatic dermal layer beneath skin.

Some anseriform birds associate with other bird species during the breeding season.

Anseriform birds are herbivorous and feed primarily on leaves, stems, flowers, roots, seeds of aquatic vegetation. They may also forage for insects, plankton, mollusks, crustaceans, and small fish.

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

Most anseriform taxa are considered seasonally monogamous, although multiple partner copulations within a breeding season may occur. Duration of pair bond may last for several years or more in some species. Pair bond formation involves complex courtship displays often entailing body posturing and vocalizations. Most anatids copulate on the water while anhimids copulate on land.

Anhimids are solitary nesters while anatids range from highly territorial to colonial. Most anseriform birds breed seasonally, although tropical taxa may breed year round. Nests are commonly located on or near water and are constructed of plant material. Clutch size ranges form 2-13 eggs. Anhimid egg-laying intervals are about two days, while anatids lay every 24 hours.

Male and female anhimids share incubation for a 42-45 day period, while anatid females incubate alone for a period of 22-40 days. Anseriform parents generally accompany young while feeding, providing predator protection and perhaps pointing out food items. Parental care sometimes continues beyond fledging for several weeks.

Many anatids are migratory while anhimids are predominantly sedentary with post-breeding dispersal of juveniles. Anhimids are noted for vocalizations, soaring, and long wing-sprus used in intraspecific agonistic interactions. Anatids are known for their flock formations, which sometimes number in the hundreds of thousands of individuals. While anatids spend a great deal of time in the water, anhimids are rarely seen swimming.

Anseriform birds often flock together outside the breeding season and may form groups ranging in size from a few individuals to many thousands. Anatids feed, roost, and migrate in flocks.

Screamers (anhimids) get their common name from their extremely loud, far ranging cries. Anatids vocalize vociferously during the breeding season. Anhimid vocalizations range from trumpeting to drumming while anatids whistle, honk, grunt or quack.

Humans hunt many anseriform species for sport or consumption. Some species have been domesticated for flesh, liver, and egg production. Feathers of several species are collected for use in textile industries.

Large flocks of anseriform birds may damage agricultural crops including: rice, winter wheat and barley, or potatoes.

Thirty-nine anseriform 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) and seven are listed as 'Endangered' (Anas bernieri, Anas chlorotis, Anas melleri, Anas wyvilliana, Anser cygnoides, Cairina scutulata, Oxyura leucocephala). Major threats include: introduced species, hunting and collecting, habitat destruction and agrochemical use.

Current morphological, behavioral and molecular analyses fail to refute the hypothesis of the monophyly of Anserifomes. Within Anseriformes, Anhimidae appears basal relative to Anatidae. The evolutionary relationships within Anatidae remain unclear, with the monophyly of several subfamilies and tribes vigorously debated. The evolutionary relationships between Anseriformes and other bird taxa also remain unresolved. There appears to be support for several different sister group hypotheses: anseriforms sister to galliforms (gamebirds); anseriforms sister to ciconiiforms (herons, ibises, storks); or anseriforms sister to phoenicopteriforms (flamingos).

Several Paleocene fossils are considered anseriform ancestors: Presbyornis pervetus from Utah and Mongolia; Telmabates antiquus from Argentina; P. isoni from Marlyand.

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. Anhimid fossil remains from Argentina date to the 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