Anseriformes

Greylag geese (Anser anser )

The geese birds ( Anseriformes ) form an order of birds ( Aves). The group includes, among other things, colloquially referred to as geese, ducks and swans, birds, but also for example the military birds of South America. Anseriformes are among the most important groups of birds in the wetlands of the earth.

Features

Geese birds have a bouncing solid body with a relatively small head, which is often at a long neck in general. The beak is apart from the military birds broad and flattened; at its peak is often a hardening that serves the pluck of plant material, while small at the edges made ​​of horn " teeth ", the blades are, which help filter out edible particles from the water.

Another characteristic feature is the webbing between the three forward-facing toes, which are much reduced form, however, in the military and the birds Spaltfußgans ( Anseranas semipalmata ). As the name suggests, they are used for rapid locomotion in water.

The plumage is waterproof and colorful patterned in many species, especially in the males. There is a constant care undergone by a water-repellent oil secreted by a lying on the body and stimulated by the beak gland and is then distributed by cleaning the feathers over the whole body. In the moulting most species lose all their feathers at the same time; the males show at this time usually a very subtle plumage drawing that serves them in their flightless condition for camouflage from predators. The thermal insulation is ensured by a thick layer of down feathers and a layer of fat located under the skin.

In contrast to other groups of birds in which the males either do not or only have a simply constructed penis are among the geese birds, the copulatory organs very well developed.

Flight

Most geese birds are excellent fliers; the Bar-headed Goose (Anser indicus) is even the highest flying bird ever. Many species lay as migratory birds return long walks between their breeding grounds and wintering areas, which may be thousands of miles long.

Habitat and diet

Geese birds usually live close to the water, in swamps and bogs, estuaries or shorelines of rivers or coastal waters. Some species spend most of their lives on the open sea and only return to breed on land back.

Most seek their food on or near the water surface, others dive for aquatic plants, while notably geese, swans and Screamers also feed on land, among other grasses and herbs that they abäsen. Anseriformes regularly swallow small stones that are used in the muscular stomach as gastroliths for grinding food.

Phylogeny

Although from the Cretaceous fragmentary fossils are known which were sometimes held for Anseriformes, the oldest unequivocal geese bird comes from the Paleocene. It is Presbyornis, which is more closely related than to military birds according to the analyzes of Livezey with the ducks birds. The fossil bird was initially thought to be a relative of the Avocet or the flamingos before Harrison and Walker 1976 placed him in the vicinity of the Anseriformes.

From the Paleocene and Eocene exclusively Presbyornis is known. Only in the Oligocene appear more fossil Anseriformes, but they seem to have been rare in this period. In the Miocene there was an explosive radiation with formation of the currently known types.

System

The monophyly of Anseriformes has been recognized for a long time. That the externally different Screamers belong to this group, was already suspected based on morphological similarities in 1863 by William Kitchen Parker. Subsequent analyzes confirmed this and showed that the Screamers are the sister group of all other extant Anseriformes.

The two ornithologists Storrs Lovejoy Olson and Feduccia took the morphology of fossil Presbyornis as a reason to suspect a relationship of geese birds to the Charadriiformes. Other scientists rejected this theory because it is based on only a single synapomorphy. Other possible relationships have been made ​​to the gallinaceous birds, the walking birds and flamingos. A sister group relationship between geese and chickens birds currently find most supporters, the common taxon is called Galloanserae.

We distinguish ten families of geese birds, seven of which are extinct. Of the remaining three, two, taken together, only four species, and the overwhelming remainder of 169 species belongs to the family Anatidae.

• Screamers ( Anhimidae )
• Spaltfußgänse ( Anseranatidae )
• Ducks ( Anatidae ) with geese, swans and ducks.
• Presbyornithidae with four fossil species of the Paleocene and Eocene, which are counted to the genus Presbyornis. They are the oldest known Anseriformes.
• Romainvillidae, only known species is Romainvillia stehlini from the Eocene / Oligocene, geese large, morphologically mediates between Spaltfuß and Pfeifgänsen.
• Cygnopteridae with three species in the genus from the Oligocene and Miocene Cygnopterus; they were often mistaken for fossil swans, earning the ornithologist Bradley C. Livezey opinion but the rank of a separate family.
• Brontornithidae with the only known genus Brontornis, a giant flightless bird from the Miocene of South America, but the "terror birds " ( Phorusrhacidae ) is assigned in many, especially older publications.
• Paranyrocidae with the only known type Paranyroca magna, a swan large bird of the Miocene of North America.
• Thunder Birds ( Dromornithidae ) giant, flightless birds with seven fossil species from the Oligocene to the Pleistocene of Australia.

Cited sources

The information in this article originate for the most part the limits given in literature sources, in addition, the following sources are cited: