Bird

Birds Temporal range: Upper Cretaceous-Present 72–0 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Ornithurae
Class:	Aves Linnaeus, 1758[1]
Synonyms
Neornithes Gadow, 1883

Birds (Aves) are a group of animals with backbones. They evolved from dinosaurs. Technically, birds are dinosaurs.^[2]

Birds are warm blooded. Their feathers help prevent loss of body heat.^[3][4] Modern birds do not have teeth. They have beaked jaws. Birds lay hard-shelled eggs. They have a high metabolic rate and a strong but lightweight skeleton. Their hearts have four chambers.

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. There are about ten thousand species of birds. More than half of these are passerines, or perching birds.

Birds have wings. The wings develop differently in different species. The only known groups of birds without wings are the extinct moa and the elephant birds. Wings evolved from the forelimbs of birds. They give birds the ability to fly. Over time, many groups of birds evolved with smaller wings. These include ratites, penguins and many island species of birds. The digestive and respiratory systems of birds are also adapted for flight. Some bird species in aquatic environments have evolved as good swimmers. This is seen in seabirds and some waterbirds.

In general, birds inherit their behaviour almost entirely. The key elements of their lives are inherited.^[5] It was a great discovery that birds never learn to fly.^[6][7][8][9] It is wrong to say when a chick waves its wings in the nest that "it is learning to fly". What the chick is doing is exercising its muscles. If they are a species that flies, they develop the ability automatically. If they are species that migrates, 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, An example of this is when they search for food.

Several bird species make and use tools. Some social species pass on some knowledge across generation. This is a form of culture. Birds are social animals. They communicate with visual signals as well as with calls and bird songs. Most of their social behaviours are inherited. Examples of this include flocking, mobbing of predators and cooperative breeding and hunting, ^[10][11]

Most bird species are socially monogamous; they usually mate for one breeding season at a time. They may mate for years. It is rare that these birds will mate for life. Other species are polygynous, in these species, one male will mate with many females. Birds species are rarely polyandrous. In these species, one female will mate with many males. Birds produce offspring by laying eggs. The eggs are fertilised by sexual reproduction. The eggs are often laid in a nest and incubated by the parents. Most birds take care of their offspring after hatching. Some birds, such as chickens, lay eggs even when not fertilised. 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 and undomesticated birds are called game birds. Songbirds, parrots and other types of birds are popular as pets. Guano is bird manure. It is harvested for use as a fertiliser. Birds figure throughout human culture. About 120–130 species of birds have become extinct because of human activity since the 17th century. Many more species had become extinct before then. Human activity threatens about 1,200 bird species with extinction, Things are being done to protect them.^[12] Recreational bird-watching is an important part of the ecotourism industry.

1. ↑ Brands, Sheila (14 August 2008). "Systema Naturae 2000 / Classification, Class Aves". Project: The Taxonomicon. Archived from the original on 5 May 2008. Retrieved 11 June 2012.
2. ↑ Chiappe L.M. & Dyke G.J. 2002. The Mesozoic radiation of birds. Annual Review of Ecology and Systematics 33:91–124.
3. ↑ McNeil Alexander R. 1975. The Chordates. Cambridge University Press. ISBN 0 521 20472 0. Chapter 11: Birds.
4. ↑ Prum, Richard O. 1999. Development and evolutionary origin of feathers. Journal of Experimental Zoology Part B: Molecular and Developmental Evolution. 285 (4): 291–306. [1]
5. ↑ Huxley, Julian 1930. Bird-watching and bird behaviour. London: Chatto & Windus, p83 et seq.
6. ↑ Spalding D.A. 1872. Instinct in young birds. Nature 6, 485–6.
7. ↑ Spalding D.A. 1873. Macmillan's Magazine 27, 282–293. Popular Science Monthly gives the same content: [2] Archived 2021-07-09 at the Wayback Machine
8. ↑ Spalding D.A. 1876. Instinct and Acquisition. Popular Science Monthly 8.
9. ↑ Lorenz, Konrad 1966, Chapter 7. Evolution and modification of behaviour. London: Methuen.
10. ↑ Burton R. 1985. Bird behavior. Alfred A. Knopf. ISBN 0-394-53957-5
11. ↑ Attenborough, David 1998. The Life of Birds. Princeton: Princeton University Press. ISBN 0-691-01633-X
12. ↑ Norris K. & Pain D. (eds) 2002. Conserving bird biodiversity: general principles and their application. Cambridge University Press. ISBN 978-0-521-78949-3