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Bird

2007 Schools Wikipedia Selection. Related subjects: Birds

   iBirds

                    Fossil range: Late Jurassic - Recent

   Superb Fairy-wren, Malurus cyaneus, juvenile
   Superb Fairy-wren, Malurus cyaneus, juvenile
                Scientific classification

   Kingdom:   Animalia
   Phylum:    Chordata
   Subphylum: Vertebrata
   (unranked) Archosauria
   Class:     Aves
              Linnaeus, 1758

                                   Orders

   Many - see section below.

   Birds are bipedal, warm-blooded, oviparous vertebrate animals
   characterized primarily by feathers, forelimbs modified as wings, and
   (in most) hollow bones.

   Birds range in size from the tiny hummingbirds to the huge Ostrich and
   Emu. Depending on the taxonomic viewpoint, there are about 8,800–10,200
   living bird species (and about 120–130 that have become extinct in the
   span of human history) in the world, making them the most diverse class
   of terrestrial vertebrates.

   Birds feed on nectar, plants, seeds, insects, fish, mammals, carrion,
   or other birds.

   Most birds are diurnal, or active during the day, but some birds, such
   as the owls and nightjars, are nocturnal or crepuscular (active during
   twilight hours), and many coastal waders feed when the tides are
   appropriate, by day or night.

   Many birds migrate long distances to utilise optimum habitats (e.g.,
   Arctic Tern) while others spend almost all their time at sea (e.g. the
   Wandering Albatross). Some, such as Common Swifts, stay aloft for days
   at a time, even sleeping on the wing.

   Common characteristics of birds include a bony beak with no teeth, the
   laying of hard-shelled eggs, high metabolic rate, a 4-chambered heart,
   and a light but strong skeleton. Most birds are characterised by
   flight, though the ratites are flightless, and several other species,
   particularly on islands, have also lost this ability. Flightless birds
   include the penguins, ostrich, kiwi, and the extinct Dodo. Flightless
   species are vulnerable to extinction when humans or the mammals they
   introduce arrive in their habitat. The Great Auk, flightless rails, and
   the moa of New Zealand, for example, all became extinct due to human
   influence.

   Birds are among the most extensively studied of all animal groups.
   Hundreds of academic journals and thousands of scientists are devoted
   to bird research, while amateur enthusiasts (called birdwatchers,
   twitchers or, more commonly, birders) probably number in the millions.

High-level taxonomy

   Birds are categorised as a biological class, Aves. The earliest known
   species of this class is Archaeopteryx lithographica, from the Late
   Jurassic period. Modern phylogenies place birds in the dinosaur clade
   Theropoda. According to the current consensus, Aves and a sister group,
   the order Crocodilia, together are the sole living members of an
   unranked "reptile" clade, the Archosauria.

   Phylogenetically, Aves is usually defined as all descendants of the
   most recent common ancestor of modern birds (or of a specific modern
   bird species like Passer domesticus), and Archaeopteryx.

   Modern birds are divided into two superorders, the Paleognathae (mostly
   flightless birds like ostriches), and the wildly diverse Neognathae,
   containing all other birds.

Bird orders

   Relationships between bird orders according the Sibley-Ahlquist
   taxonomy. "Galloanseri" is now considered a superorder Galloanserae.
   Enlarge
   Relationships between bird orders according the Sibley-Ahlquist
   taxonomy. "Galloanseri" is now considered a superorder Galloanserae.

   This is a list of the taxonomic orders in the subclass Neornithes, or
   modern birds. The list of birds gives a more detailed summary of these,
   including families.

   SUBCLASS NEORNITHES
   Paleognathae:
     * Struthioniformes, Ostrich, emus, kiwis, and allies
     * Tinamiformes, tinamous

   Neognathae:
     * Anseriformes, waterfowl
     * Galliformes, fowl
     * Gaviiformes, loons
     * Podicipediformes, grebes
     * Procellariiformes, albatrosses, petrels, and allies
     * Sphenisciformes, penguins
     * Pelecaniformes, pelicans and allies
     * Ciconiiformes, storks and allies
     * Phoenicopteriformes, flamingos
     * Accipitriformes, eagles, hawks and allies
     * Falconiformes, falcons
     * Gruiformes, cranes and allies
     * Charadriiformes, gulls, button-quail, plovers and allies
     * Pteroclidiformes, sandgrouse
     * Columbiformes, doves and pigeons
     * Psittaciformes, parrots and allies
     * Cuculiformes, cuckoos, turacos, hoatzin
     * Strigiformes, owls
     * Caprimulgiformes, nightjars and allies
     * Apodiformes, swifts and hummingbirds
     * Coraciiformes, kingfishers
     * Piciformes, woodpeckers and allies
     * Trogoniformes, trogons
     * Coliiformes, mousebirds
     * Passeriformes, passerines

   Note: This is the traditional classification (the so-called Clements
   order). A radically different classification based on molecular data
   has been developed (the so-called Sibley-Monroe classification or
   Sibley-Ahlquist taxonomy). This has influenced taxonomical thinking
   considerably, with the Galloanserae proving well-supported by recent
   molecular, fossil and anatomical evidence. With increasingly good
   evidence, it has become possible by 2006 to test the major proposals of
   the Sibley-Ahlquist taxonomy. The results are often nothing short of
   astounding, see e.g. Charadriiformes or Caprimulgiformes.

Extinct bird orders

   A wide variety of bird groups became extinct during the Mesozoic era
   and left no modern descendants. These include the orders
   Archaeopterygiformes, Confuciusornithiformes, toothed seabirds like the
   Hesperornithes and Ichthyornithes, and the diverse subclass
   Enantiornithes ("opposite birds").

   For a complete listing of prehistoric bird groups, see Fossil birds.
   Shoebill, Balaeniceps rex
   Enlarge
   Shoebill, Balaeniceps rex

Evolution

   There is significant evidence that birds evolved from theropod
   dinosaurs, specifically, that birds are members of Maniraptora, a group
   of theropods which includes dromaeosaurs and oviraptorids, among
   others. As more non-avian theropods that are closely related to birds
   are discovered, the formerly clear distinction between non-birds and
   birds becomes less so. Recent discoveries in northeast the People's
   Republic of China ( Liaoning Province), demonstrating that many small
   theropod dinosaurs had feathers, contribute to this ambiguity.

   The basal bird Archaeopteryx, from the Jurassic, is well-known as one
   of the first "missing links" to be found in support of evolution in the
   late 19th century, though it is not considered a direct ancestor of
   modern birds. Confuciusornis is another early bird; it lived in the
   Early Cretaceous. Both may be predated by Protoavis texensis, though
   the fragmentary nature of this fossil leaves it open to considerable
   doubt if this was a bird ancestor. Other Mesozoic birds include the
   Enantiornithes, Yanornis, Ichthyornis, Gansus and the
   Hesperornithiformes, a group of flightless divers resembling grebes and
   loons.

   The recently discovered dromaeosaur Cryptovolans was capable of powered
   flight, possessed a sternal keel and had ribs with uncinate processes.
   In fact, Cryptovolans makes a better "bird" than Archaeopteryx which is
   missing some of these modern bird features. Because of this, some
   paleontologists have suggested that dromaeosaurs are actually basal
   birds whose larger members are secondarily flightless, i.e. that
   dromaeosaurs evolved from birds and not the other way around. Evidence
   for this theory is currently inconclusive, but digs continue to unearth
   fossils (especially in China) of the strange feathered dromaeosaurs. At
   any rate, it is fairly certain that avian flight existed in the
   mid-Jurassic and was "tried out" in several lineages and variants by
   the mid-Cretaceous.
   Snowy Owl, Bubo scandiacus
   Enlarge
   Snowy Owl, Bubo scandiacus

   Although ornithischian (bird-hipped) dinosaurs share the same hip
   structure as birds, birds actually originated from the saurischian
   (lizard-hipped) dinosaurs (if the dinosaurian origin theory is
   correct), and thus arrived at their hip structure condition
   independently. In fact, the bird-like hip structure also developed a
   third time among a peculiar group of theropods, the Therizinosauridae.

   An alternate theory to the dinosaurian origin of birds, espoused by a
   few scientists (most notably Lary Martin and Alan Feduccia), states
   that birds (including maniraptoran "dinosaurs") evolved from early
   archosaurs like Longisquama, a theory which is contested by most other
   scientists in paleontology, and by experts in feather development and
   evolution such as R.O. Prum. See the Longisquama article for more on
   this alternative.

   Modern birds are classified in Neornithes, which are now known to have
   evolved into some basic lineages by the end of the Cretaceous (see
   Vegavis). The Neornithes are split into the Paleognathae and
   Neognathae. The paleognaths include the tinamous (found only in Central
   and South America) and the ratites. The ratites are large flightless
   birds, and include ostriches, cassowaries, kiwis and emus (though some
   scientists suspect that the ratites represent an artificial grouping of
   birds which have independently lost the ability to fly in a number of
   unrelated lineages). The basal divergence from the remaining Neognathes
   was that of the Galloanseri, the superorder containing the Anseriformes
   ( ducks, geese and swans), and the Galliformes (the pheasants, grouse,
   and their allies). See the chart for more information.

   The classification of birds is a contentious issue. Sibley & Ahlquist's
   Phylogeny and Classification of Birds (1990) is a landmark work on the
   classification of birds (although frequently debated and constantly
   revised). A preponderance of evidence seems to suggest that the modern
   bird orders constitute accurate taxa. However, scientists are not in
   agreement as to the relationships between the orders; evidence from
   modern bird anatomy, fossils and DNA have all been brought to bear on
   the problem but no strong consensus has emerged. More recently, new
   fossil and molecular evidence is providing an increasingly clear
   picture of the evolution of modern bird orders. See also:
   Sibley-Ahlquist taxonomy.
   Anatomy of a typical bird
   Enlarge
   Anatomy of a typical bird

Bird anatomy

   Birds have a body plan that shows so many unusual adaptations (mostly
   aiding flight) that birds have earned their own unique class in the
   vertebrate phylum.

   Unlike mammals, birds don't urinate. Their kidneys extract nitrogenous
   wastes from the bloodstream, but instead of excreting it as urea
   dissolved in urine as we do, they excrete it in the form of uric acid.
   Uric acid has a very low solubility in water, so it emerges as a white
   paste. This material, as well as the output of the intestines, emerges
   from the bird's cloaca. The cloaca is a multi-purpose hole for birds:
   their wastes come out of it, they have sex by putting their cloacas
   together, and females lay eggs out of it.

   Birds have one of the most complex lung system of all organisms. Air
   enters the bird and immediately 75% of the air bypasses the lungs and
   flows directally into a posterior air sac which extends from the lungs
   and connects with air spaces in the bones and fills them with air. When
   the bird exhales the air from the postirior air sac is forced into the
   lungs thus birds receive a supply of air during both inhalation and
   exhalation. The gas exchange then takes place in the capillaries.

   The nervous system relative to the birds size is actually quite large.
   The most developed part of the brain is the one that controls the
   flight related function while the cerebellum coordinates movement and
   the cerebrum controls behaviour patterns, navigation, mating and nest
   building. A birds eyes are developed for taking off, spotting
   landmarks, hunting and feeding. Birds with eyes on the side of their
   head have a wide vision field while birds with eyes on the front of
   their heads like owls have binocular vision and can measure depth.

Nesting

Eggs

   All birds lay amniotic eggs with hard shells made mostly of calcium
   carbonate. Non-passerines typically have white eggs, except in some
   ground-nesting groups such as the Charadriiformes, sandgrouse and
   nightjars, where camouflage is necessary, and some parasitic cuckoos
   which have to match the passerine host's egg. Most passerines, in
   contrast, lay coloured eggs, even if, like the tits they are
   hole-nesters.

   The brown or red protoporphyrin markings on passerine eggs reduce
   brittleness and are a substitute for calcium when that element is in
   short supply. The colour of individual eggs is genetically influenced,
   and appears to be inherited through the mother only, suggesting that
   the gene responsible for pigmentation is on the sex determining W
   chromosome (female birds are WZ, males ZZ).

   The eggs are laid in a nest, which may be anything from a bare cliff
   ledge or ground scrape to elaboratey decorated structures such as those
   of the oropendolas.

Social systems and parental care

   The three mating systems that predominate among birds are polyandry,
   polygyny, and monogamy. Monogamy is seen in approximately 91% of all
   bird species. Polygyny constitutes 2% of all birds and polyandry is
   seen in less than 1%. Monogamous species of males and females pair for
   the breeding season. In some cases, the individuals may pair for life.

   One reason for the high rate of monogamy among birds is the fact that
   male birds are just as adept at parental care as females. In most
   groups of animals, male parental care is rare, but in birds it is quite
   common; in fact, it is more extensive in birds than in any other
   vertebrate class. In birds, male care can be seen as important or
   essential to female fitness. "In one form of monogamy such as with
   obligate monogamy a female cannot rear a litter without the aid of a
   male" .
   These Redwing hatchlings are completely dependent on parental care.
   Enlarge
   These Redwing hatchlings are completely dependent on parental care.

   The parental behaviour most closely associated with monogamy is male
   incubation. Interestingly, male incubation is the most confining male
   parental behaviour. It takes time and also may require physiological
   changes that interfere with continued mating. This extreme loss of
   mating opportunities leads to a reduction in reproductive success among
   incubating males. "This information then suggests that sexual selection
   may be less intense in taxa where males incubate, hypothetically
   because males allocate more effort to parental care and less to mating"
   . In other words, in bird species in which male incubation is common,
   females tend to select mates on the basis of parental behaviors rather
   than physical appearance.

Birds and humans

   Chinstrap Penguin, Pygoscelis antarctica
   Enlarge
   Chinstrap Penguin, Pygoscelis antarctica
   A birdbox is an artificial platform for birds to make a nest
   Enlarge
   A birdbox is an artificial platform for birds to make a nest

   Birds are an important food source for humans. The most commonly eaten
   species is the domestic chicken and its eggs, although geese,
   pheasants, turkeys, and ducks are also widely eaten. Other birds that
   have been utilized for food include emus, ostriches, pigeons, grouse,
   quails, doves, woodcocks, songbirds, and others, including small
   passerines such as finches. Birds grown for human consumption are
   referred to as poultry.

   At one time swans and flamingos were delicacies of the rich and
   powerful, although these are generally protected now.

   Besides meat and eggs, birds provide other items useful to humans,
   including feathers for bedding and decoration, guano-derived phosphorus
   and nitrogen used in fertilizer and gunpowder, and the central
   ingredient of bird's nest soup.

   Humans have caused the disappearance of some bird species. The
   Passenger Pigeon and Dodo were hunted to extinction, and many others
   have become endangered or extinct through habitat destruction (e.g. by
   deforestation or intensive agriculture).

   Some species have come to depend on human activities for food and are
   widespread to the point of being pests. For example, the common pigeon
   or Rock Pigeon (Columba livia) thrives in urban areas around the world.
   In North America, introduced House Sparrows, European Starlings, and
   House Finches are similarly widespread.

   Other birds have long been used by humans to perform tasks. For
   example, homing pigeons were used to carry messages before the advent
   of modern instant communications methods (many are still kept for
   sport). Falcons are still used for hunting, while cormorants are
   employed by fishermen. Chickens and pigeons are popular as experimental
   subjects, and are often used in biology and comparative psychology
   research. As birds are very sensitive to toxins, the Canary was used in
   coal mines to indicate the presence of poisonous gases, allowing miners
   sufficient time to escape without injury.

   Colorful, particularly tropical, birds (e.g. parrots, and mynas) are
   often kept as pets although this practice has led to the illegal
   trafficking of some endangered species; CITES, an international
   agreement adopted in 1963, has considerably reduced trafficking in the
   bird species it protects.

   Bird diseases that can be contracted by humans include psittacosis,
   salmonellosis, campylobacteriosis, Newcastle's disease, mycobacteriosis
   (avian tuberculosis), avian influenza, giardiasis, and
   cryptosporidiosis.

Threats to birds

   According to Worldwatch Institute, bird populations are declining
   worldwide, with 1,200 species facing extinction in the next century.
   Among the biggest cited reasons are habitat loss, predation by
   nonnative species, oil spills and pesticide use, hunting and fishing,
   and climate change.

Trivia

     * To preen or groom their feathers, birds use their bills to brush
       away foreign particles.
     * The birds of a region are called the avifauna.
     * Few birds use chemical defences against predators. Tubenoses can
       eject an unpleasant oil against an aggressor, and some species of
       pitohui, found in New Guinea, secrete a powerful neurotoxin in
       their skin and feathers.
     * The Latin word for bird is avis.

   Retrieved from " http://en.wikipedia.org/wiki/Bird"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
   of authors and sources) and is available under the GNU Free
   Documentation License. See also our Disclaimer.
