Anatidae

"Waterbird" redirects here. See also shorebirds and seabirds.
Ducks, geese and swans
Black-bellied Whistling Duck (Dendrocygna autumnalis)
Black-bellied Whistling Duck (Dendrocygna autumnalis)
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Subclass: Neornithes
Infraclass: Neognathae
Superorder: Galloanserae
Order: Anseriformes
Family: Anatidae
Vigors, 1825
Subfamilies

Anatinae
Anserinae
Aythyinae
Dendrocygninae
Merginae
Oxyurinae
Plectropterinae
Stictonettinae
Tadorninae
Thalassorninae
and see text

Anatidae is the biological family that includes the ducks, geese and swans. The family has a cosmopolitan distribution, occurring on all the world's continents except Antarctica and on most of the world's islands and island groups. These are birds that are evolutionarily adapted for swimming, floating on the water surface, and in some cases diving in at least shallow water. (The Magpie-goose is no longer considered to be part of the Anatidae, but is placed in its own family Anseranatidae.) The family contains around 146 species in 40 genera. They are generally herbivorous, and are monogamous breeders. A number of species undertake annual migrations. A few species have been domesticated for agriculture, and many others are hunted for food and recreation. Five species have become extinct since 1600, and many more are threatened with extinction.

Contents

Description and ecology

The ducks, geese and swans are small to large sized birds that have a general body plan that is broad and elongated.[1] Diving species vary from this in being rounder. Extant species range in size from the Cotton Pygmy Goose, at as little as 26.5 cm (10.5 inches) and 164 grams (5.8 oz), to the Trumpeter Swan, at as much as 183 cm (6 ft) and 17.2 kg (38 lb). The wings are short and pointed, and supported by strong wing muscles that generate rapid beats in flight. They typically have long necks, although this varies in degree between species. The legs are short and strong and set far to the back of the body, more so in the more aquatic species. Combined with their body shape this can make some species awkward on land, but they are stronger walkers than other marine and water birds such as grebes or petrels. They have webbed feet. The bills of most species are flattened to a greater or lesser extent. These contain serrated lamellae which are particularly well defined in the filter-feeding species.[1]

Their feathers are excellent at shedding water due to special oils. Many of the ducks display sexual dimorphism, with the males being more brightly coloured than the females (although the situation is reversed in species like the Paradise Shelduck). The swans, geese and whistling-ducks lack sexually dimorphic plumage. Anatids are vocal birds, producing a range of quacks, honks, squeaks, and trumpeting sounds, depending on species; the female often has a deeper voice than the male[2].

Anatids are generally herbivorous as adults, feeding on various water-plants, although some species also eat fish, molluscs, or aquatic arthropods. One group, the mergansers, are primarily piscivorous, and have a serrated bill to help them catch fish. In a number of species, the young include a high proportion of invertebrates in their diet, but become purely herbivorous as adults[2].

Breeding

The anatids are generally seasonal and monogamous breeders. The level of monogamy varies within the family, many of the smaller ducks only maintain the bond for a single season and find a new partner the following year, whereas the larger swans, geese and some of the more territorial ducks maintain pair bonds over a number of years. Anatidae are remarkable for being one of the few families of birds that possess a penis;[3] most species are adapted for copulation on the water only. They construct simple nests from whatever material is close to hand, often lining them with a layer of down plucked from the mother's breast. In most species, only the female incubates the eggs. The young are precocial, and are able to feed themselves from birth[2]. One aberrant species, the Black-headed Duck, is an obligate brood parasite, laying its eggs in the nests of gulls and coots. While this species never raises its own young, a number of other ducks will occasionally lay eggs in the nests of conspecifics (members of the same species) in addition to raising their own broods.

Relationship with humans

Duck, eider, and goose feathers and down have long been popular for bedspreads, pillows, sleeping bags and coats. The members of this family also have long been used for food.

Humans have had a long relationship with ducks, geese and swans; they are important economically and culturally to humans, and several duck species have benefited from an association with people. On the flip side some anatids are damaging agricultural pests, and have acted as vectors for zoonosis such as avian influenza.

Since 1600 five species of duck have become extinct due to the activities of humans, and subfossil remains have shown that humans caused numerous extinctions in prehistory. Today many more are considered threatened. Most of the historic and prehistoric extinctions were insular species, these species were vulnerable due to small populations (often endemic to a single island), and island tameness. Evolving on islands that lacked predators these species lost anti-predator behaviours as well as the ability to fly, and were vulnerable to human hunting pressure and introduced species. Other extinctions and declines are attributable to overhunting, habitat loss and modification, as well as hybridisation with introduced ducks (for example the introduced Ruddy Duck swamping the White-headed Duck in Europe). Numerous governments, conservation and hunting organisations have made considerable progress in protecting ducks and duck populations through habitat protection and creation, laws and protection, and captive breeding programmes.

Systematics

While the status of the Anatidae as a family is straightforward, and there is little debate about which species properly belong to it, the relationships of the different tribes and subfamilies within it are poorly understood. The listing in the box at right should be regarded as simply one of several possible ways of organising the many species within the Anatidae; see discussion in the next section.

The systematics of the Anatinae is in a state of flux. Previously divided into six subfamilies, a study of anatomical characters by Livezey[4] suggest that the Anatidae are better treated in nine subfamilies. This classification was popular in the late 1980s to 1990s[5]. But mtDNA sequence analyses[6] indicate that for example the dabbling and diving ducks do not belong in the same subfamily. While there are certainly shortcomings in Livezey's analysis, mtDNA is an unreliable source for phylogenetic information in many waterfowl (especially dabbling ducks) due to their ability to produce fertile hybrids[1], in rare cases possibly even beyond the level of genus (see for example the "Barbary Duck"). Due to the small sample size of many molecular studies available to date, mtDNA results must be considered with caution.

But while a comprehensive review of the Anatidae which unites all evidence into a robust phylogeny is still lacking, the reasons for the confusing data are at least clear: As demonstrated by the Late Cretaceous fossil Vegavis iaai — an early modern waterbird which belonged to an extinct lineage — the Anatidae are an ancient group among the modern birds. Their earliest direct ancestors, though not documented by fossils yet, likewise can be assumed to have been contemporaries with the dinosaurs. The long period of evolution and shifts from one kind of waterbird lifestyle to another have obscured many plesiomorphies, while apomorphies apparently are quite often the result of parallel evolution, for example the "non-diving duck" type displayed by such unrelated genera as Dendrocygna, Amazonetta, and Cairina. For the fossil record, see below.

Alternatively[7], the Anatidae may be considered to consist of 3 subfamilies (ducks, geese, and swans, essentially) which contain the groups as presented here as tribes, with the swans separated as subfamily Cygninae, the goose subfamily Anserinae also containing the whistling ducks, and the Anatinae containing all other clades.

Genera

Species known from bones only

From subfossil bones found on Kauaʻi (Hawaiian Islands), two enigmatic waterfowl are known[11]. The living and assignable prehistoric avifauna of the archipelago contains as Anseriformes Branta geese and their descendants, and the moa-nalos as mentioned above. The following taxa, although certainly new species, cannot be assigned even to subfamily; that Kauaʻi is the oldest of the large Hawaiian Islands, meaning the species may have been evolving in isolation for nearly up to 10 mya (since the Late Miocene), does not help in determining their affinities:

Similarly, Wetmore's Goose (Geochen rhuax) from the Big Island of Hawaiʻi, and a gigantic goose-like anatid from Oʻahu are known only from very incomplete and in the former case much damaged bone fragments. The former has been alleged to be a shelduck[12], but this was generally dismissed because of the damage to the material and biogeographic considerations. The long-legged Kauaʻi bird, however, hints at the possibility of a former tadornine presence on the archipelago.

Fossil Anatidae

The fossil record of anatids is extensive, but many prehistoric genera cannot be unequivocally assigned to present-day subfamilies for the reasons given above. Some (such as Eonessa) seem to belong to subfamilies which are completely extinct. For prehistoric species of extant genera, see the respective genus accounts.

Eonessinae - extinct ancient anatids

Dendrocheninae - a more advanced relative of the whistling-ducks or a more ancestral relative of stifftail ducks paralleling whistling-ducks; probably extinct but Malacorhynchus might belong here

Anserinae

Tadorninae

Anatinae

Oxyurinae

incertae sedis

Putative or disputed prehistoric anatids are:

Footnotes

  1. ↑ 1.0 1.1 1.2 Carboneras (1992)
  2. ↑ 2.0 2.1 2.2 Todd, Frank S. (1991). Forshaw, Joseph. ed.. Encyclopaedia of Animals: Birds. London: Merehurst Press. pp. 81-87. ISBN 1-85391-186-0. 
  3. ↑ McCracken, Kevin G. (2000): "The 20-cm Spiny Penis of the Argentine Lake Duck (Oxyura vittata)". The Auk 117(3) p.820–825.
  4. ↑ 4.0 4.1 4.2 4.3 Livezey (1986)
  5. ↑ E.g. Madge & Burn (1987)
  6. ↑ Sraml et al. (1996), Johnson & Sorenson (1999)
  7. ↑ e.g. Terres & NAS (1991)
  8. ↑ Johnson & Sorenson (1999)
  9. ↑ Collar et al. (2001)
  10. ↑ Johnson & Sorenson (1999)
  11. ↑ Burney et al. (2001)
  12. ↑ Short (1970)
  13. ↑ Gál et al. (1998-99)

References

External links