View source for Bird

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{{Automatic taxobox
|name = Birds
| fossil_range = <br />{{fossilrange|160|0|[[Lower Cretaceous]]–[[Holocene|present]], 160 mya – present| | earliest=160.8}}
<imagemap>
File:Bird Diversity 2013.png|300px
rect 0 0 333 232 [[Red-crested turaco]]
rect 0 232 333 470 [[Steller's sea eagle]]
rect 0 696 333 470 [[Rock dove]]
rect 0 928 333 700 [[Southern cassowary]]
rect 0 1160 333 930 [[Gentoo penguin]]
rect 0 1392 333 1160 [[Bar-throated minla]]

rect 666 0 333 232 [[shoebill]]
rect 666 232 333 470 [[grey crowned crane]]
rect 666 696 333 470 [[Anna's hummingbird]]
rect 666 928 333 700 [[rainbow lorikeet]]
rect 666 1160 333 930 [[grey heron]]
rect 666 1392 333 1160 [[Eurasian eagle-owl]]

rect 999 0 333 232 [[white-tailed tropicbird]]
rect 999 232 333 470 [[Indian peafowl]]
rect 999 696 333 470 [[Atlantic puffin]]
rect 999 928 333 700 [[American flamingo]]
rect 999 1160 333 930 [[blue-footed booby]]
rect 999 1392 333 1160 [[keel-billed toucan]]
</imagemap>
|image_caption = Examples of various avian orders.
Row 1: [[Red-crested turaco]], [[shoebill]], [[white-tailed tropicbird]]<br />Row 2: [[Steller's sea eagle]], [[grey crowned crane]], [[common peafowl]]<br />Row 3: [[Great hornbill]], [[Anna's hummingbird]], [[Atlantic puffin]]<br />Row 4: [[Southern cassowary]], [[rainbow lorikeet]], [[American flamingo]]<br />Row 5: [[Gentoo penguin]], [[grey heron]], [[blue-footed booby]]<br />Row 6: [[Bar-throated minla]], [[Eurasian eagle-owl]], [[keel-billed toucan]]
|taxon = Aves
|authority = [[Carl Linnaeus|Linnaeus]], [[10th edition of Systema Naturae|1758]]<ref name=brands>{{cite web| url= http://taxonomicon.taxonomy.nl/TaxonTree.aspx?id=80129&tree=0.1| title=Systema Naturae 2000 / Classification, Class Aves | accessdate=11 June 2012 | last=Brands | first=Sheila | date=14 August 2008 | work=Project: The Taxonomicon }}</ref>
|subdivision_ranks = Living [[Order (biology)|Orders]]
|subdivision =
| synonyms =
* Neornithes <small>Gadow, 1883</small>
}}
[[File:Birdmorphology.svg|thumb|upright=1.35|alt= |right|External anatomy of a bird (example: [[yellow-wattled lapwing]]): 1 Beak, 2 Head, 3 Iris, 4 Pupil, 5 Mantle, 6 Lesser [[covert (feather)|coverts]], 7 Scapulars, 8 Median coverts, 9 Tertials, 10 Rump, 11 Primaries, 12 [[Cloaca#Birds|Vent]], 13 Thigh, 14 Tibio-tarsal articulation, 15 Tarsus, 16 Foot, 17 Tibia, 18 Belly, 19 Flanks, 20 Breast, 21 Throat, 22 Wattle, 23 Eyestripe]]

[[File:BirdBeaksA.svg|thumb|right|230px|Bird [[beak]]s as [[adaptations]]]]

'''Birds''' ('''Aves''') are a group of [[vertebrate|animals with backbone]]s which [[evolved]] from [[dinosaur]]s. Technically speaking, they are dinosaurs.<ref>Chiappe L.M. & Dyke G.J. 2002. The Mesozoic radiation of birds. ''Annual Review of Ecology and Systematics'' '''33''':91{{ndash}}124.</ref> 

Birds are [[Thermoregulation|endothermic]]. The heat loss from their bodies is slowed down by their [[feather]]s.<ref>McNeil Alexander R. 1975. ''The Chordates''. Cambridge University Press. ISBN 0 521 20472 0. Chapter 11: Birds.</ref><ref>Prum, Richard O. 1999. Development and evolutionary origin of feathers. ''Journal of Experimental Zoology'' Part B: Molecular and Developmental Evolution. '''285''' (4): 291–306. [https://web.archive.org/web/20110409103417/http://ncsce.org/PDF_files/feathers/Prum%20feather.pdf]</ref> 
Modern birds are [[Tooth|toothless]]: they have [[Beak|beaked]] [[jaw]]s. They [[Oviparous animals|lay]] [[cleidoic egg|hard-shelled]] eggs. They have a high [[metabolic rate]], a four-chambered [[heart]] and a strong yet lightweight [[skeleton]].

Birds live all over the world. They range in size from the 5 cm (2 in) [[bee hummingbird]] to the 2.70 m (9 ft) [[ostrich]]. They are the [[tetrapods]] with the most living species: about ten thousand. More than half of these are [[passerine]]s, sometimes known as perching birds.

Birds are the closest living relatives of the [[Crocodilia]]. This is because they are the two main survivors of a once huge group called the [[Archosaurs]].<ref name=Benton>Benton M.J. 4th ed. ''Vertebrate palaeontology''. Wiley-Blackwell, p154 ''et seq''.</ref> 

Modern birds are ''not'' descended from ''[[Archaeopteryx]]''. According to [[DNA]] evidence, ''modern'' birds (Neornithes) evolved in the long [[Upper Cretaceous]] period.<ref name=Lee>Lee, Michael SY; Cau, Andrea; Darren, Naish; Gareth J. & Dyke 2014. Morphological clocks in paleontology, and a mid-Cretaceous origin of crown Aves. ''Systematic Biology''. '''63''' (1): 442–449.</ref> More recent estimates showed that  modern birds originated early in the Upper Cretaceous.

Primitive bird-like dinosaurs are in the broader group [[Avialae]].<ref>{{Cite book|last=Gauthier |first=Jacques|editor=Kevin Padian |title=The origin of birds and the evolution of flight|series= Memoirs of the California Academy of Science '''8'''|year=1986|pages=1–55|chapter=Saurischian monophyly and the origin of birds |isbn=0-940228-14-9 |publisher=Published by California Academy of Sciences |location=San Francisco, CA}}</ref> They have been found back to the [[Middle Jurassic|mid-Jurassic]] period, around 170 million years ago. Many of these early "stem-birds", such as ''[[Anchiornis]]'', were not yet capable of fully powered flight. Many had [[primitive]] characteristics like teeth in their jaws and long bony tails.<ref name=Lee/><ref name=Benton/><sup>p274</sup>

The [[Cretaceous–Palaeogene extinction event]] 66 million years ago killed off all the non-avian dinosaur lines. Birds, especially those in the southern continents, survived this event and then migrated to other parts of the world.<ref>Influence of Earth's history on the dawn of modern birds. www.sciencedaily.com. ''American Museum of Natural History'' 2015. [https://www.sciencedaily.com/releases/2015/12/151211145038.htm]</ref> Diversification occurred around the [[Cretaceous–Palaeogene extinction event]].<ref name=cracraft>{{cite journal |last1=Claramunt |first1=S. |last2=Cracraft |first2=J. |title=A new time tree reveals Earth history's imprint on the evolution of modern birds |journal=Sci Adv |date=2015 |volume=1 |issue=11 |doi=10.1126/sciadv.1501005 |pmc=4730849 |pmid=26824065 |page=e1501005|bibcode=2015SciA....1E1005C }}</ref> 

Birds have wings which are more or less developed depending on the species. The only known groups without wings are the extinct [[moa]] and [[elephant bird]]s. Wings, which evolved from forelimbs, gave birds the ability to fly. Later, many groups evolved with reduced wings, such as [[ratites]], [[penguins]] and many island species of birds. The digestive and [[respiratory system]]s of birds are also adapted for flight. Some bird species in aquatic environments, particularly [[seabirds]] and some waterbirds, have evolved as good swimmers.

In general, birds are effective, and [[heredity|inherit]] their behaviour almost entirely. The key elements of their life are inherited.<ref>Huxley, Julian 1930. ''Bird-watching and bird behaviour''. London: Chatto & Windus, p83 et seq.</ref> It was a great discovery that birds never learn to fly.<ref>Spalding D.A. 1872. Instinct in young birds. ''Nature'' '''6''', 485–6.</ref><ref> Spalding D.A. 1873. ''Macmillan's Magazine'' '''27''', 282–293. Popular Science Monthly gives the same content: [https://en.wikisource.org/wiki/Popular_Science_Monthly/Volume_2/March_1873/Instinct_in_Young_Birds]</ref><ref>Spalding D.A. 1876. Instinct and Acquisition. ''Popular Science Monthly'' '''8'''.</ref><ref>Craig W. 1918. Appetites and aversions as constituents of instincts. ''Biol. Bull''. '''34''': 91–107.</ref><ref>Gray P.H. 1961. Verification of Spalding's method for controlling visual experience by hooding chicks in the shell. ''Proc. Montana Acad. Sci''. '''21''', 120–3.</ref><ref>Lorenz, Konrad 1966, Chapter 7. ''Evolution and modification of behaviour''. London: Methuen.</ref> 
So it is quite wrong to say, when a chick waves its wings in the nest "It's learning to fly". What the chick is doing is exercising its muscles. They develop the ability to fly ''automatically'' (assuming they are species that do fly). And if they are species which [[migrate]], that behaviour is also inherited. Many species [[migrate]] over great distances each year. Other main features of their life may be inherited, though they can and do learn. Birds have good memories which they use, for example, when they search for food.

Several bird species make and use tools. Some social species pass on some knowledge across generations, a form of [[culture]]. Birds are social. They communicate with visual signals, calls and [[bird song]]s. Most of their social behaviours are inherited, such as cooperative breeding and hunting, flocking and [[mobbing]] of predators.<ref>Burton R. 1985. ''Bird behavior''. Alfred A. Knopf. ISBN 0-394-53957-5</ref><ref name=David>Attenborough, David 1998. ''The Life of Birds''. Princeton: Princeton University Press. ISBN 0-691-01633-X</ref>

Most bird species are socially [[Monogamy|monogamous]], usually for one breeding season at a time, sometimes for years, but rarely for life. Other species are [[Polygyny|polygynous]] (one male with many females) or, rarely, [[Polyandry|polyandrous]] (one female with many males). Birds produce offspring by laying eggs which are fertilised by [[sexual reproduction]]. They are often laid in a nest and incubated by the parents. Most birds have an extended period of parental care after hatching. Some birds, such as hens, lay eggs even when not fertilised, though unfertilised eggs do not produce offspring.

Many species of birds are eaten by humans. Domesticated and undomesticated birds are sources of eggs, meat, and feathers.  In English, domesticated birds are often called [[poultry]], undomesticated birds are called [[game bird|game]]. Songbirds, parrots and other species are popular as [[Pet|pets]]. [[Guano]], which is bird [[manure]], is harvested for use as a [[fertiliser]]. Birds figure throughout human culture. About 120–130 species have become [[extinct]] due to human activity since the 17th century and hundreds more before then. Human activity threatens about 1,200 bird species with extinction, though efforts are underway to protect them.<ref>Norris K. & Pain D. (eds) 2002. ''Conserving bird biodiversity: general principles and their application''. Cambridge University Press. ISBN 978-0-521-78949-3</ref> Recreational [[bird-watching]] is an important part of the ecotourism industry.

== Bird colours ==
[[File:Male and female pheasant.jpg|thumb|230px|Female (left) and male common [[pheasant]], illustrating the difference in colour (and also size)]]

Birds come in a huge range of colours.<ref>Lysaght A.M. 1975. ''The book of birds: five centuries of bird illustrations''. New York: Phaidon. ISBN 0 7148 1667 1.</ref> These colours can be useful to a bird in two ways. [[Camouflage]] colours help to hide the bird, and bright colours identify the bird to others of the same species. Often the male is brightly coloured while the female is camouflaged. The logic is as follows: the female carries the "precious package" of developing eggs. The male has to defend a [[Territory (animal)|territory]], and the function of his colour and song is to let others know that "this place is occupied".<ref>Cott, Hugh B. 1940. ''Adaptive colouration in animals''. London: Methuen, part II: Advertisement.</ref>

=== Bird camouflage ===
[[File:Perdix perdix (Marek Szczepanek).jpg|thumb|right|230px|Grey [[partridge]]s can hide in grass easily]]
[[Image:African Scops owl.jpg|thumb|right|230px|This Scops [[owl]] is almost invisible against the tree]]

Many birds are brown, green or grey. These colours make a bird harder to be seen: they [[camouflage]] the bird.<ref name=Cott>Cott, Hugh B. 1940. ''Adaptive colouration in animals''. London, Methuen.</ref> Brown is the most common colour. Brown birds include: [[sparrow]]s, [[Emu|emus]], [[Turdidae|thrushes]], [[Lark|larks]], [[Eagle|eagles]] and [[Falcon|falcons]] and the female birds of many species such as: [[Wren|wrens]], [[Duck|ducks]], [[Blackbird|blackbirds]] and [[Peafowl|peafowls]]. When a brown bird is in long grass or among tree trunks or rocks, it is ''camouflaged''.<ref>Forbes P. 2009. ''Dazzled and deceived: mimicry and camouflage''. New Haven. Yale University Press. ISBN 978-0-300-12539-9</ref> Birds that live in long grass often have brown feathers streaked with black which looks like shadows. A [[bittern]] is almost invisible in long reeds because its camouflage is helped by its posture (beak and head pointed upwards). Other birds, including [[starling]]s and [[myna]]s, are quite dark in colour, but are flecked with little spots that look like raindrops on leaves. Bird may also camouflage their nests.

Many birds from hot countries are green or have some green feathers, particularly [[parrot]]s. Birds that live in green trees often have green backs, even if they have bright-coloured breasts. From the back, the birds are camouflaged. This is very useful when sitting on a nest.<ref>Wolf, Art 2005. ''Vanishing act''. New York: Bullfinch. ISBN 0-8212-5750-1</ref> The bird's bright-coloured breast is hidden. [[Budgerigar]]s are bred in different colours such as blue, white and mauve, but in the wild, they are nearly all green and yellow. Even though they fly very well, they normally spend a lot of time on the ground, eating [[grass]] seeds. Their yellow and black striped back helps to hide them in the shadows made by long dry grass, while their green breasts are a similar colour to the leaves of [[gum tree]]s.

Grey birds include most [[pigeon]]s and [[dove]]s, [[Crane (bird)|cranes]], [[stork]]s and [[heron]]s. Grey birds are often rock-living birds like pigeons or birds that sit on dead tree trunks looking like a broken branch. Water birds like herons often have a pale grey colour which makes it harder for a fish to notice that the bird is standing, looking down for something to catch. Water birds, no matter what colour they are on top, are often white underneath, so that when a fish looks up, the bird looks like part of the sky.

Black birds include [[crow]]s, [[raven]]s and male [[blackbird]]s. Some birds that are dark colours spend quite a lot of time on the ground, hopping around in the shadows under bushes. Among these birds are the male blackbird and the [[satin bowerbird]] which is not black but very dark blue. Crows and ravens often perch high on bare trees in the winter, where their black shape against the sky looks like the dark bare branches.

=== Noticeable colours ===
[[File:Pair of mandarin ducks.jpg|thumb|right|250px|Pair of [[mandarin duck]]s. A good example of a general rule: male birds are the showy ones, females are dowdy]]

Many birds are not [[camouflaged]], but stand out with vivid colours. They are usually male birds whose females are dull and camouflaged. The function of the colours is two-fold.<ref name=Cott/> First, the colours help them get mates, and second, the colours identify them to other males of the same species. Many birds are territorial, especially in the nesting season. They give out territory sounds and are easily seen. This lets other males know they will defend their territory. It sends out a "look elsewhere" signal to their competitors.

Some birds are famous for their colour and some are named for it, such as the [[bluebird]], the [[azure kingfisher]], the [[golden pheasant]], the [[scarlet macaw]]. The [[European robin]] is known popularly as the red robin.

Many other birds are very brightly coloured, in countless combinations. Some of the most colourful birds are quite common, like pheasants, peacocks, domestic fowl and parrots. Colourful small birds include [[blue tit]]s, the [[goldfinch]]es, [[hummingbirds]], fairy [[wren]]s and bee eaters (which are also called rainbow birds). Some birds, like those of the [[bird of paradise]] in [[Papua New Guinea]] have such beautiful feathers that they have been hunted for them.

The [[peafowl]] is the best example of a display of colour to attract a mate. Also the male domestic fowl and [[junglefowl]] have long shiny feathers above his tail and also long neck feathers that may be a different colour to his wings and body. There are only a few species of birds (such as the [[eclectus parrot]]) where the female is more colourful than the male.
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<nowiki>''Pied birds''</nowiki> are black and white. Black and white birds include [[magpie]]s, pied [[Goose|geese]], [[Pelican|pelicans]] and Australian [[Magpie|magpies]] (which are not really magpies at all). Pied birds often have brightly coloured beaks and legs of yellow or red. The silver pheasant, with its long white tail striped with fine bars of black, has a brightly coloured face.

<gallery>
File:Austkingparrot.jpg|King [[parrot]], [[Australia]]
File:Common.shelduck.2.arp.750pix.jpg|Common shel[[duck]]
File:Alcedo atthis 2 (Lukasz Lukasik).jpg|[[Kingfisher]]
File:Lightmatter flamingo2.jpg|[[Flamingo]]
File:Oriole 2.jpg|Golden [[oriole]].
File:Tarsiger rufilatus - Doi Inthanon.jpg|Himalayan bluetail
File:Hydrornis irena - Sri Phang Nga.jpg|Malayan banded pitta
</gallery>

== Flight ==
Most birds can fly, and if they do, then the ability is inherited, not learnt.<ref>The person who proved this was [[Douglas Spalding]].</ref> They fly by pushing through the air with their wings. The curved surfaces of the wings cause air currents (wind) which lift the bird. Flapping keeps the air current moving to create lift and also moves the bird forward.<ref>Alexander, David E. 2002. ''Nature's flyers: birds, insects, and the biomechanics of flight''. Baltimore: The Johns Hopkins University Press. ISBN 0-8018-6756-8</ref><ref>Baumel J.J. 1993. ''Handbook of Avian Anatomy'': Nomina Anatomica Avium. Cambridge: Nuttall Ornithological Club. pp. 45–46, 128.</ref>

Some birds can glide on air currents without flapping. Many birds use this method when they are about to land. Some birds can also hover in the air. This method is used by birds of prey such as [[falcon]]s that are looking for something to eat. Seagulls are also good at hovering, particularly if there is a strong breeze. The most expert hovering birds are tiny [[Hummingbird|hummingbirds]] which can beat their wings both backwards and forwards and can stay quite still in the air while they dip their long beaks into flowers to feed on the sweet [[nectar]]. 
<gallery>
Image:Flock-of-tundra-swans.jpg| A flock of tundra [[swan]]s fly in V-formation.
Image:OspreyNASA.jpg|This [[osprey]] at Kennedy Space Centre is hovering. 
Image:Wandering Albatross (van Poppel).jpg|A wandering [[albatross]] can sleep while flying.
File:Cathartes aura 2.jpg|The large broad wings of a [[vulture]] allow it to soar without flapping. 
File:Australian barn owl.jpg|The soft feathers of an [[owl]] allow it to fly quietly.
File:California Quail with babies.JPG|Some birds, such as the [[quail]], live mainly on the ground.
File:Casuarius casuarius -Brevard Zoo-8a.jpg|A [[cassowary]] cannot fly but it can defend itself. 
Image:Schwimmender-Pinguin.jpg|[[Penguin]]'s flippers are good for swimming.
</gallery>

=== Types of flight ===
Different types of birds have different needs.<ref>As a matter of fact, we know that dinosaurs developed wings a number of times in their evolution from small dinosaur raptors. Benton, Michael [https://www.youtube.com/watch?v=O9NMQf_RfZw]</ref> Their wings have [[Adaptation|evolved]] to suit their [[lifestyle]].<ref>Videler J.J. 2005. ''Avian flight''. Oxford University Press. ISBN 0-19-856603-4</ref> Large birds of prey, such as [[eagle]]s, spend a lot of time soaring on the wind. They have wings that are large and broad. The main flight feathers are long and wide. They help the eagle to stay on rising air currents without using much energy, while the eagle looks at the ground below, to find the next meal. When the eagle sees some small creature move, it can close its wings and fall from the sky like a missile, opening its great wings again to slow down as it comes to land. The world's largest eagle, the [[Philippine eagle]] has a wingspan of about 2 m (6.7&nbsp;ft) wide.

Birds that live in grassland areas or open forests and feed on fruit, insects and reptiles often spend a lot of time flying short journeys looking for food and water. They have wings that are shaped in a similar way to eagles, but rounder and not as good for soaring. These include many Australian birds like [[cockatoo]]s.<ref name=David/>

Birds such as [[geese]] that migrate from one country to another fly very long distances. Their wings are big and strong, because the birds are large. They stock up on food for the long flight.<ref>Carboneras, Carles 1992. Family Anatidae (ducks, geese and swans). In del Hoyo, Josep; Elliott, Andrew; Sargatal, Jordi (eds) ''Handbook of Birds of the World. Volume 1: Ostrich to Ducks''. Barcelona: Lynx Edicions. pp. 536–629. ISBN 84-87334-10-5</ref> [[Migration|Migrating]] [[water bird]]s usually form family groups of 12{{ndash}}30 birds. They fly very high, making use of long streams of air that blow from north to south in different seasons. They are well organised, often flying in a V pattern. The geese at the back do not have to flap so hard; they are pulled on by the wind of the ones at the front. Every so often, they change the leader so that the front bird, who does most work and sets the pace, can have a rest. Geese and [[swan]]s are the highest-flying birds, reaching 8,000 metres or more when on migration. Geese often ''honk'' loudly while they are flying. It is thought that they do this to support the leader and help the young ones.

Birds that fly very quickly, such as [[swift]]s and [[swallow]]s, have long narrow pointed wings. These birds need great speed because they eat insects, catching most of them while they are flying. These birds also migrate. They often collect in huge flocks of thousands of birds that move together like a whirling cloud.

Birds that live in bushes and branches have triangular wings that help the bird change direction. Many forest birds are expert at getting up speed by flapping and then gliding steadily among the trees, tilting to avoid things as they go. 

Birds such as owls that hunt at night have wings with soft rounded feathers so that they do not flap loudly. Birds that are awake at night are called ''nocturnal'' birds. Birds that are awake during the day are ''diurnal''.

[[Wandering albatross]] might spend several years without coming to land. They can sleep while gliding.<ref>Tickell W.L.N. 2000. ''Albatrosses''. Sussex: Pica Press. ISBN 1-873403-94-1</ref> [[Arctic tern]]s nest every one to three years.<ref>Hatch J.J. Arctic Tern (''Sterna paradisaea''), in Poole A. & Gill F. (eds) ''The Birds of North America''. Philadelphia, PA. </ref>

=== Flocks ===
Flocks of birds can be very highly organised in a way that takes care of all the flock members. Studies of small flocking birds like tree [[Sparrow|sparrows]] show that they clearly communicate with each other, as sometimes thousands of birds may fly in close formation and [[spiral]] patterns without colliding (or flying into each other).<ref> Gill, Frank 2007. ''Ornithology''. New York, NY: W.H. Freeman and Company.</ref>

Two common behaviours in flocking birds are guarding and reconnaissance. When a flock of birds is feeding it is common for one bird to perch on a high place to keep guard over the flock. In the same way, when a flock is asleep, often, one bird will remain awake. It is also common for large flocks to send one or two birds ahead of them when they are flying to a new area. The look-out birds can spy the lie of the land to find food, water and good places to perch.<ref>These two behaviours have often been observed in the Australian sulphur crested cockatoo which may have given its name "Cocky" to the person who keeps a look-out for the police during a [[burglary]].</ref> Mixed feeding flocks occur, and can help to spot predators.<ref>Terborgh J 2005. Mixed flocks and polyspecific associations: costs and benefits of mixed groups to birds and monkeys. ''American Journal of Primatology''. '''21''' (2): 87–100. [https://pubmed.ncbi.nlm.nih.gov/31963979/]</ref>

=== Flightless birds ===
Some birds do not fly.<ref>Roots C. 2006. ''Flightless birds''. Westport: Greenwood Press. ISBN 978-0-313-33545-7</ref> Flightlessness in birds has evolved many times.
These include running birds like [[ostrich]]es and [[emu]]s and ocean-living birds, the large [[penguin]] family. Birds on islands have usually lost the power of flight. This is to their advantage because birds with the power of flight can be blown off their island during a storm. The same ability which got them to the island may later take them away in a storm.<ref name=Savol>Sayol F. et al. 2020. Anthropogenic extinctions conceal widespread evolution of flightlessness in birds. ''Science Advances''. '''6''' (49):eabb6095, DOI: 10.1126/sciadv.abb6095. [https://advances.sciencemag.org/content/6/49/eabb6095/tab-pdf]</ref>

Ostriches and emus do not need to fly because although they feed and nest on the ground, their great size and their speed is their protection. Some other ground-feeding birds have not been so lucky. Some birds such as the [[dodo]] and the kiwi were ground-feeding birds that lived in safety on islands where there was nothing dangerous to eat them. They lost the power of flight. Kiwis are endangered because European settlement to [[New Zealand]] brought animals like [[Cat|cats]], [[Dog|dogs]] and [[Rat|rats]] which kill [[Kiwi|kiwis]] and eat their eggs. However, kiwis and also the rare New Zealand ground parrot have survived. In the case of [[dodo]]s, they were fat and disgusting in taste. All the same, they were killed and eaten by sailors until there was none left. Other flightless birds which have disappeared are the [[great auk]] and the [[moa]].<ref name=Savol/>

Penguins are a very successful group of birds.<ref name=Ksepka>Ksepka D.T; Bertelli, Sara & Giannini, Norberto P. 2006. The phylogeny of the living and fossil Sphenisciformes (penguins). ''Cladistics''. '''22''' (#5): 412–441. </ref> They are a [[clade]]. They spend half their time on land. Their wings are adapted to life in the sea and have become flippers which let them in swim fast. They catch fish at sea, where they are in danger from [[Pinniped|seals]].

=== Preening ===
Preening is how birds keeps their feathers in order. They use their beak to position feathers, interlock feather barbules that have become separated, clean plumage, and keep [[ectoparasite]]s in check. 

Feathers in good shape help the bird's [[insulation]], waterproofing and flight. Their condition is vital to the bid's survival.

== Digestion ==
Modern birds do not have teeth, and many swallow their prey whole. Nevertheless, they must break up food before it is digested. First of all, along their throat ([[oesophagus]]) they have a '''crop'''. This stores food items before [[digestion]]. That way a bird can eat several items, and then fly off to a quiet spot to digest them. 

Their [[stomach]] comes next, with two very different parts. One part is like a straight hollow rod (the ''proventriculus'') which secretes mild [[hydrochloric acid]] and an [[enzyme]] to break down [[protein]]. The other part of the stomach is the [[gizzard]]. This is muscular, and grinds up the contents. In [[herbivorous]] birds the gizzard contains some [[gastrolith]]s (small stones or pieces of grit). Bones of fish will mostly be dissolved by the stomach acid. The partly digested and ground-up food now goes to the intestine, where digestion is completed, and most contents are absorbed. Anything indigestible, for example remains of feathers, is [[regurgitate]]d via the mouth, not the [[cloaca]].<ref>Zaher, Mostafa 2012. Anatomical, histological and histochemical adaptations of the avian alimentary canal to their food habits: I-Coturnix coturnix. ''Life Science Journal'' '''9''': 252–275. [https://www.researchgate.net/publication/281656486_Anatomical_histological_and_histochemical_adaptations_of_the_avian_alimentary_canal_to_their_food_habits_I-Coturnix_coturnix]</ref>

The system is effective, and carnivorous birds can swallow quite large prey. A blue [[heron]] can swallow a fish as large as a [[carp]] successfully.<ref>Blue heron swallows large prey. [https://www.youtube.com/watch?v=1v5w0UK2SvE]</ref> [[Bird of prey|Raptors]] eat by holding the prey down with a foot, and tearing it apart with their [[beak]].

== Reproduction == 
=== Mating ===
Although birds are warm-blooded creatures like [[mammal]]s, they do not give birth to live young. They lay [[cleidoic egg|eggs]] as reptiles do, but the shell of a bird's egg is hard. The baby bird grows inside the egg, and after a few weeks hatches (breaks out of the egg).
[[File:SwansHeart.jpg|thumb|250px|Swans mate for life]]

Birds in cold climates usually have a breeding season once a year in the spring. Migratory birds can have two springs and two mating seasons in a year. 

Ninety-five per cent of bird species are socially [[monogamous]].<ref>Freed, Leonard A. 1987. The long-term pair bond of tropical house wrens: advantage or constraint?. ''The American Naturalist''. '''130''' (4): 507–525. doi:10.1086/284728</ref> These birds pair for at least the length of the breeding season. In some cases this arrangement lasts until the death of one of the pair. Monogamy clearly helps if females need males' help to raise a brood successfully.<ref>{{Cite journal|last=Gowaty|first=Patricia A.|title=Male parental care and apparent monogamy among Eastern Bluebirds (''Sialia sialis'')|url=https://archive.org/details/sim_american-naturalist_1983-02_121_2/page/149|journal=The American Naturalist|volume=121|issue=2|pages=149–160|year=1983|doi=10.1086/284047|s2cid=84258620}}</ref> It has other practical advantages: the nest is never left without defence. Birds are generally small, and they have many potential enemies.

Some birds mate for life, like married couples. These birds include [[pigeon]]s, [[goose|geese]], and cranes. Other birds look for new partners each year. For birds that choose new mates, part of the breeding season is display. The male bird will do all sorts of things to attract females. These include singing, dancing, showing off the feathers and building a beautiful nest. Some male birds have splendid feathers for attracting females. The most famous is the [[peacock]] who can spread the feathers above his tail into a huge fan. 
<gallery>
Image:Pfau imponierend.jpg|A [[peacock]] display  
Image:Sarus.jpg|The [[sarus crane]], like most [[Crane (bird)|cranes]], mates for life and pairs dance 
Image:SperlingG.jpg|A nest of [[house sparrow]]s
Image:Emu Gelege.jpg|[[Emu]] nest 
</gallery>

Other mating systems do occur in some species. [[Polygyny]], [[polyandry]], [[polygamy]], [[polygynandry]], and [[promiscuity]] do happen.<ref name = Gill/> Polygamous breeding systems arise when females are able to raise broods without the help of males.<ref name=Gill>Gill, Frank 1995. ''Ornithology''. New York: Freeman. ISBN 0-7167-2415-4</ref> Some species may use more than one system depending on the circumstances.

=== Nesting ===
Once the birds have found partners, they find a suitable place to lay eggs. The idea of what is a suitable place differs between species, but most build [[bird nest]]s. The bird is driven by a hormone ([[estradiol]] E2) to prepare a place for the eggs to hatch.<ref> Meurisse J. Gonzalez A. Delsol, G. Caba M. Levy F. Poindron P. 2005. Estradiol receptor-α expression in hypothalamic and limbic regions of ewes is influenced by physiological state and maternal experience. ''Hormones and Behavior''. '''48''' (1): 34–43. [https://pubmed.ncbi.nlm.nih.gov/15919383/]</ref> Birds' nests may be up a tree, in a cliff or on the ground according to species. When filled with eggs they are almost always guarded by one of the pair. In fact it is virtually impossible for the eggs to survive if one of the parents dies.

Robins will make a beautiful little round nest of woven grass and carefully line it with feathers, bits of fluff and other soft things. [[Swallow]]s like to nest near other swallows. They make nests from little blobs of clay, often on a beam near the roof of a building where it is well sheltered. Many birds like a hollow tree to nest in. [[Eagle]]'s nests are often just piles of dead wood on the top of the tallest tree or mountain. Scrub [[Turkey (bird)|turkeys]] scratch together a huge pile of leaves that may be 10 metres across. Guillemots lay their eggs on rock shelves with no nest at all. Their eggs are shaped so that they roll around in circles and do not fall off cliffs. A [[cuckoo]] does not make its own nest. It lays its egg in the nest of another bird and leaves it for them to care for. The cuckoo eggs are [[camouflage]]d to look like the host's eggs.

When the nest has been prepared, the birds mate so that the eggs are fertilised and the chicks will start growing. Unlike mammals, birds (and reptiles) only have one opening as the exit hole for body [[fluid]]s, and for [[reproduction]]. The opening is called the [[cloaca]]. A female bird, called a hen, has two ovaries, of which the left one usually produces eggs.

Most male birds have no sex organs that can be seen. But inside the male are two [[testicle|testes]] which produce [[sperm]] which is stored in the cloaca. Birds mate by rubbing their cloacas together, although with some birds, particularly large water birds, the male has a sort of a [[penis]] inside the cloaca.

=== Hatching ===
Once the hen has mated, she produces fertile eggs which have chicks growing inside them. She lays the eggs in the nest. There might be just one egg or a number of them, called a clutch. [[Emu]]s might lay as many as fifteen huge dark green eggs in a clutch. After the eggs are laid, they are incubated, or kept warm so the chicks form inside. Most birds stay together for the whole nesting season, and one advantage is that the work is shared. Many birds take turns sitting on the eggs, so that each adult can feed.

This is not always the case. With emus, the male does all the sitting and all the baby-minding. With [[emperor penguin]]s it is also the male that cares for the egg. There is only one egg, which he keeps on his feet and under his feathers, standing in a big group of males without feeding until the chick is hatched. While the eggs are hatching, the females are at sea, catching fish, so that they can feed the chicks when they return.

Some birds put the eggs inside or on top of the mound of leaves and twigs. The mound acts like a [[compost]] heap. The [[decomposer|decomposition]] of the rotting leaves causes the temperature to rise. This is heat released by the chemical action of [[bacteria]]l and [[fungi|fungal]] [[respiration]]. It is the same reaction as that which keeps mammals and birds at a high temperature. The parents leave the mound. When the chicks hatch, they are able to feed themselves.

Many small birds take 2–4 weeks to hatch eggs. [[Albatross|Albatrosses]] take 80 days. During this time the female loses a lot of her body weight.

The quickest hatching time is for the [[cuckoo]]. Some types of cuckoos take only 10 days. This means that when they hatch in the nest of their <nowiki>''foster parents''</nowiki>, the eggs that the parents have laid are not yet ready. Newborn cuckoos are naked, blind and ugly, but they are strong. They get under any eggs that are in the nest and throw them out before they hatch. That means that the cuckoo has the whole care of both parents. Baby cuckoos grow fast and often get bigger than the parents who feed them.

When baby birds hatch, in most types of birds, they are fed by both parents, and sometimes by older aunts as well. Their mouths are open all the time and are often very brightly coloured, which acts as a ''[[releaser]]'', a trigger which stimulates the parent to feed them. For birds that eat grain and fruit, the parents eat and partly digest the food for the babies. It is then [[vomit|vomi]]ted carefully into the baby's mouth.
  
<gallery>
File:Hausrotschwanz Brutpflege 2006-05-24 211.jpg|A black redstart feeding chicks
File:Cygnus atratus -adult with chicks in Australia-8.jpg|[[Black swan]] and [[cygnet]]s
File:Reed warbler cuckoo.jpg|A reed warbler feeding a baby [[cuckoo]]
File:Yellow-crested Cockatoo.jpg|Two [[sulphur crested cockatoo]]s from a big flock are on the lookout 
</gallery>

=== Families ===
Many birds, particularly those that mate for life, are very sociable and keep together in a family group which might be anything from 4 or 6 adult birds and their young to a very large flock.

As chicks grow they change the fluffy down that covers them as babies for real feathers. At this stage they are called fledglings. Other family members may help care for fledgling chicks, feeding them and protecting them from attack while parents are feeding. When the fledglings have their new feathers, they come out of the nest to learn to fly. In some types of birds, like pigeons, the parents watch over this and as the young ones get stronger, will give them flying lessons, teaching them how to glide, how to fly in spirals and how to land like an expert.

== Communication ==
Most birds are social animals, at least part of the time. They communicate to each other using sounds and [[display (zoology)|displays]].

Almost all birds make [[bird sound|sounds]] to [[Communication|communicate]]. The types of noises that vary greatly. Some birds can sing, and  they are called songbirds or [[passerine]]s. Examples are [[European robin|robins]], [[lark]]s, [[canary|canaries]], [[Turdidae|thrush]]es, [[nightingale]]s. [[Corvid]]s are passerines, but they do not sing. Birds that are not songbirds include: [[pigeon]]s, [[seagull]]s, [[eagle]]s, [[owl]]s and [[ducks]]. [[Parrots]] are not songbirds, even though they can be taught to sing human songs.
<gallery>
File:Erithacus rubecula (Marek Szczepanek).jpg|A favourite songbird, the [[European robin]].
File:Rooster02.jpg|The crow of the [[rooster]] is a familiar bird call.
File:Currawong in peppercorn.jpg|The pied [[currawong]], an outstanding singer.
File:Jackdaw.northdevon.arp-sh.750pix.jpg|The [[jackdaw]]s helped Lorenz to understand bird communication.  
</gallery>

=== Songbirds ===
All birds make noises (<nowiki>''bird vocalisation''</nowiki>), but not all sing. Songbirds are [[passerine]]s, many of which have beautiful melodic songs.<ref>Lucy Hodson [https://www.bbc.co.uk/programmes/articles/34jF1nwh8Z32sbB92dH23yf/listen-and-learn-a-beginner-s-guide-to-identifying-birdsong?xtor=CS8-1000-[Discovery_Cards]-[Multi_Site]-[SL06]-[PS_SOUNDS~N~~A_ABeginnersGuideToBirdSong]</ref> Songs have different functions. Danger cries are different from territorial songs and mating calls are a third type. Fledgling may also have different calls from adults. Recognition calls for partners are quite common.

As to where the song comes from, there are three kinds of [[species]]:
#Those where the song is mainly [[heredity|inherited]], and the bird always sings the same song in the same situations. The capacity is inherited, and only details are learnt from its neighbours.
#Those where the song is partly inherited, but the bird tunes it in by copying others. In this case the slight differences between the calls of different birds may be used by partners for identification.<ref>Thorpe W.H. 1958. The learning of song patterns by birds, with especial reference to the song of the chaffinch ''Fringilla coelebs''. ''Birds'' '''100''', 4, p535-570. [https://onlinelibrary.wiley.com/doi/10.1111/j.1474-919X.1958.tb07960.x]</ref>
#Those where the song is entirely learnt, and the bird often copies sounds from its [[environment]]. Only the capacity to sing is inherited.

Most singing birds that are kept as pets, like canaries, have several tunes and some variations.

The same species of bird will sing different songs in different regions. A good example of this is the [[currawong]]. This is an Australia bird which is like a black and white crow. In the autumn, families get together in large flocks and do a lot of singing. Currawongs from some areas sing much more complex songs than others. Generally, currawongs from the [[Blue Mountains (New South Wales)|Blue Mountains]] are the finest singers. The song of the currawong can be sung as a solo, but is often performed as a [[choir (music)|choir]]. One bird will take the lead and sing "Warble-warble-warble-warble!" All the other birds will join in and sing "Wooooooo!". When all the birds know the song, the choir will sing the "Warble" part and the soloist will sing the "Woo!". The song changes from year to year and from place to place.

=== Lorenz's studies ===
The [[Austria]]n naturalist [[Konrad Lorenz]] studied the way in which birds communicate, or talk to each other. He found that each type of bird had a number of sounds which they made automatically, when ever they felt a certain way. Every sound had an action that went with it. So, if the bird was frightened, it acted frightened and made a frightened sound. This told the other birds around it that something frightening was happening.

If a flock of birds were flying over a field, they would be calling "Fly! Fly!" But a hungry bird, seeing something good to eat down below might start calling "Food! Food!" If other birds were also hungry, they would make the same call until more birds were calling "Food! Food!" than "Fly! Fly!". At this point, the mind of the flock would be changed. Some of the birds would start to yell "Fly downwards! Fly downwards!" as they sank from the sky, until the whole flock was all noisily calling the same thing.

These communication sounds are often short hard sounds like: chirps, squeaks, squawks and twitters. Sometimes the calls are longer and more musical. They include the "Rookety-coo" sound of a pigeon and the "Cockadoodledoo!" of a rooster. The bird cannot change these sounds. They always make them in the same way. The bird is locked into making each sound every time a particular idea comes into its head. The connection between how they feel and how they call is [[innate behaviour|innate]]: they are born with it. Some calls in some species are learnt. Then, it is the tendency to learn which is inherited.

==== The Jackdaw of Altenberg ====
Konrad Lorenz noticed that when birds sing, they often use a lot of their regular calls as part of the song. Lorenz had a flock of [[jackdaw]]s which were scattered during [[World War II]]. One day, an old bird returned. For many months she sat on the chimney singing her song, but in the song she kept making the call which Lorenz knew meant "Come home! Come home!" One day, to the great surprise of Lorenz, a male bird flew from a passing flock and joined her on the chimney. Lorenz was sure that it was her long-lost "husband" who had found his way home at last.<ref>Lorenz, Konrad 1952. ''King Solomon's ring''. London: Methuen, chapter 11 The perennial retainers.</ref>

== Evolution and taxonomy ==
{{Main|Origin of birds}}
[[File:Naturkundemuseum Berlin - Archaeopteryx - Eichstätt.jpg|alt= Slab of stone with fossil bones and feather impressions|thumb|right|''[[Archaeopteryx]]'', the earliest known bird]]
[[File:Confuciusornis sanctus (2).jpg|thumb|alt= White slab of rock left with cracks and impression of bird feathers and bone, including long paired tail feathers|''[[Confuciusornis]]'', a [[Cretaceous]] bird from [[China]]]]
[[Palaeontologists]] have found some exceptional places ([[lagerstätte]]n) where [[fossils]] of early birds are found. The preservation is so good that on the best examples impressions of their feathers can be seen, and sometimes even the remains of meals they have eaten. From these remains we know that birds evolved from small [[carnivorous]] [[dinosaur]]s ([[theropod]]s) in the [[Jurassic]] period.<ref name="Theropoda">{{cite journal  |title=Higher-order phylogeny of modern birds (Theropoda, Aves: Neornithes) based on comparative anatomy. II. Analysis and discussion |journal=Zoological Journal of the Linnean Society |volume=149 |issue=1 |pages=1–95 |doi=10.1111/j.1096-3642.2006.00293.x |pmid=18784798 |last1=Livezey |first1=BC |last2=Zusi |first2=RL |year=2007 |issn=0024-4082 |pmc=2517308}}</ref> They [[adaptive radiation|radiated]] into a huge variety in the [[Lower Cretaceous]]. At the same time, their direct competitors, the [[pterosaur]]s, dwindled in numbers and variety, and became extinct at the end of the [[Mesozoic]].

Birds are classified by [[taxonomy|taxonomists]] as 'Aves' ([[Avialae]]). Birds are the only living descendants of dinosaurs (strictly speaking, they ''are'' dinosaurs). Birds and [[Crocodilia]] are the only living members of the once-dominant [[Archosaur]] [[reptile]]s.

=== Definition ===
The [[class (biology)|class]] Aves is was defined (1990) as all the descendants of the most recent common ancestor of modern birds and ''[[Archaeopteryx|Archaeopteryx lithographica]]''.<ref> Philip J. Currie & Kevin Padian (eds) 1997. "Bird Origins"  
  in ''Encyclopedia of Dinosaurs'', Academic Press, pages 41–96.</ref> But ''Archaeopteryx'' is almost certainly ''not'' the ancestor of modern birds. The transition to flight happened a number of times.<ref name=Gautier+>Gauthier J., and de Queiroz K. 2001. Feathered dinosaurs, flying dinosaurs, crown dinosaurs, and the name Aves. pp. 7–41 in New perspectives on the origin and early evolution of birds: proceedings of the International Symposium in Honor of John H. Ostrom (J.A. Gauthier and L.F. Gall eds). Peabody Museum of Natural History, Yale University, New Haven, CT.</ref> The researchers offered four definitions. Birds can be: <ref name=Gautier+/>
#All archosaurs closer to birds than crocodiles ([[Avemetatarsalia]]).
#Advanced archosaurs with feathers ([[Avofilopluma]]).
#Those feathered dinosaurs that fly (or [[Avialae]])
#Aves can mean the last common ancestor of all living birds and all of its descendants (a "crown group", in this sense synonymous with [[Neornithes]]).

=== The first bird-like creatures ===
''Archaeopteryx'', from the [[Upper Jurassic]] some 150–145 million years ago (mya), was for a long time the earliest known bird which could fly. It is famous, because it was one of the first important fossils found after [[Charles Darwin]] published his ideas about [[evolution]] in the 19th century. By modern standards, ''Archaeopteryx'' could not fly very well.<ref>Senter P. 2006. Scapular orientation in theropods and basal birds and the origin of flapping flight. ''Acta Palaeontologica Polonica''.</ref> Other early fossil birds are, for example, ''[[Confuciusornis]]'', ''[[Anchiornis huxlei]]'' and other [[Paraves]].

Many [[fossil]]s of early birds and small dinosaurs have been discovered in the Liaoning Province of Northeast [[China]]. These include ''[[Anchiornis huxlei]]'', from about 160 mya.<ref>Longrich, Nicholas R. 2012. Primitive wing feather arrangement in ''Archaeopteryx lithographica'' and ''Anchiornis huxleyi''. ''Current Biology'' '''22''', 23, 2262-2267. [https://www.cell.com/current-biology/fulltext/S0960-9822(12)01194-3?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS0960982212011943%3Fshowall%3Dtrue]</ref> The fossils show that most small theropod dinosaurs had feathers. These deposits have preserved them so well that the impressions of their feathers can be clearly seen. This leads us to think that feathers evolved first as heat insulation and only later for flight. The [[origin of birds]] lies in these small [[feathered dinosaur]]s.

[[Palaeontology|Palaeontologists]] now agree that birds are included in [[Maniraptora]] group of [[dinosaur]]s. This explains why we say that birds are living dinosaurs.

=== Evolution of modern birds ===
A leading authority says "Most living birds have fossil representatives in the [[Cenozoic]]"... "Key problems remain in understanding bird phylogeny... we seem to understand as little about the relationships among living birds as among Cretaceous birds".<ref>Benton M.J. 2015. ''Vertebrate palaeontology'', 4th ed. Wiley-Blackwell, p274.</ref> A useful source for modern birds is Clements J. 2007. ''The Clements Checklist of Birds of the World''. Cornel University Press (6th ed).

* [[Origin of birds]]
* [[Paraves]]

== Birds and people ==
<gallery>
File:Rune i bokhyllan 5.JPG|[[Canary|Canaries]] are often kept as pets for their beautiful songs.
File:Congo African Grey pet on a perch.JPG|The African grey [[parrot]] is a renowned talker.
File:Blue-Winged Teal.jpg|Blue-winged teal [[ducks]] used to be shot for sport.
File:Mycteria leucocephala2.jpg|In many countries [[storks]] are thought to bring good luck.  
</gallery>

Some birds are eaten as food. Most usually it is the [[chicken]] and its [[Egg (food)|eggs]], but people often also eat [[goose|geese]], [[pheasant]]s, [[turkey (bird)|turkeys]] and [[duck]]s. Other birds are sometimes eaten are: [[emu]]s, [[ostrich]]es, [[pigeon]]s, [[grouse]], [[quail]]s, [[dove]]s, woodcocks and even [[songbird]]s. Some species have died out because they have been hunted for food, for example the [[dodo]] and the [[passenger pigeon]].

Many species have learned how to get food from people. The number of birds of these species has grown because of it. [[Seagull]]s and [[crow]]s find food from [[garbage]] dumps. The [[feral]] [[pigeon]] (''Columba livia''), [[sparrow]]s (''Passer domesticus'' and [[starling]]s (''Sturnus vulgaris'') live in large numbers in [[town]]s and [[city|cities]] all over the world.

Sometimes people also use working birds. For example, [[pigeon|homing pigeons]] carry messages. Nowadays people sometimes race them for [[sport]]. People also use [[falcon]]s for hunting, and [[cormorant]]s for fishing. In the past, people in [[mining|mines]] often used a [[canary]] to see if there were bad gas [[methane]] in the air.

People often have colorful birds such as [[parrot]]s and mynahs as [[pet]]s. These intelligent birds are popular because they can copy human talking. Because of this, some people trap birds and take them to other countries to sell. This is not usually allowed these days. Most pet birds are specially bred and are sold in pet shops.

People can catch some bird diseases, for example: [[psittacosis]], salmonellosis, [[Campylobacter|campylobacteriosis]], Newcastle's disease, mycobacteriosis, [[influenza]], [[Giardia lamblia|giardiasis]] and cryptosporiadiosis. In 2005, there was an epidemic of bird influenza spreading through some parts of the world, often called [[avian flu]].

Some people have [[birdbox]]es in their gardens to give birds a place to nest and bird tables where birds can get food and water in very cold or very dry weather. This lets people see some small birds close up which are normally hidden away in bushes and trees.


<gallery> 
Image:Blue Tit aka.jpg|Blue tit 
Image:Passer domesticus 02.jpg|Male house sparrow 
Image:Fringilla coelebs chaffinch male edit2.jpg|Male chaffinch 
Image:Sitta-carolinensis-001.jpg|White-breasted nuthatch
</gallery>

== Bird orders ==
The following is a listing of all bird orders:
* Infraclass [[Palaeognathae]]
** Superorder Struthionimorphae
*** [[Struthioniformes]]
** Superorder Notopalaeognathae
*** [[Rhea (bird)|Rheiformes]]
*** [[Tinamiformes]]
*** [[Casuariiformes]]
*** [[Apterygiformes]]
* Infraclass [[Neognathae]]
** Superorder [[Galloanserae]]
*** [[Galliformes]]
*** [[Anseriformes]]
** Superorder [[Neoaves]]
*** [[Phoenicopteriformes]]
*** [[Podicipediformes]]
*** [[Columbiformes]]
*** [[Mesitornithiformes]]
*** [[Pteroclidiformes]]
*** [[Apodiformes]]
*** [[Caprimulgiformes]]
*** [[Cuculiformes]]
*** [[Otidiformes]]
*** [[Musophagiformes]]
*** [[Opisthocomiformes]]
*** [[Gruiformes]]
*** [[Charadriiformes]]
*** [[Gaviiformes]]
*** [[Procellariiformes]]
*** [[Sphenisciformes]]
*** [[Ciconiiformes]]
*** [[Suliformes]]
*** [[Pelecaniformes]]
*** [[Eurypygiformes]]
*** [[Phaethontiformes]]
*** [[Cathartiformes]]
*** [[Accipitriformes]]
*** [[Strigiformes]]
*** [[Coliiformes]]
*** [[Leptosomiformes]]
*** [[Trogoniformes]]
*** [[Bucerotiformes]]
*** [[Coraciiformes]]
*** [[Piciformes]]
*** [[Cariamiformes]]
*** [[Falconiformes]]
*** [[Psittaciformes]]
*** [[Passeriformes]]
== Bird population decreasing ==
A report produced by BirdLife International every five years measures the population of birds worldwide. One in every eight types of birds is now "in decline".<ref>Devokaitis, Marc 2018. [https://www.allaboutbirds.org/2018-global-report-40-of-worlds-birds-are-in-decline/ Global Report: 40% of world’s birds are in decline]  ''All About Birds''</ref>

== Related article ==
* [[Origin of birds]]

== References ==
{{reflist}}

== External links ==
{{commons|Various birds|Aves}}

{{wikispecies}}
* [http://www.bsc-eoc.org/avibase/avibase.jsp?lang=EN&pg=home Avibase - The World Bird Database] {{Webarchive|url=https://web.archive.org/web/20081020193845/http://www.bsc-eoc.org/avibase/avibase.jsp?lang=EN |date=2008-10-20 }}
* [http://www.bird-hybrids.com/engine.php?LA=En Bird Hybrids Database - Search by bird name, use Sibley classification]
* [http://www.i-o-c.org/IOComm/index.htm International Ornithological Committee] {{Webarchive|url=https://web.archive.org/web/20100411072746/http://www.i-o-c.org/IOComm/index.htm |date=2010-04-11 }}

{{vertebrates}}
{{Taxonbar}}
{{authority control}}
[[Category:Basic English 850 words]]
[[Category:Birds| ]]
[[Category:Dinosaurs]]
[[Category:Feathered dinosaurs]]