bird

Brood parasites

Main article: Brood parasite
Reed warbler raising a common cuckoo, a brood parasite
Brood parasitism, in which an egg-layer leaves her eggs with another individual's brood, is more common among birds than any other type of organism.[245] After a parasitic bird lays her eggs in another bird's nest, they are often accepted and raised by the host at the expense of the host's own brood. Brood parasites may be either obligate brood parasites, which must lay their eggs in the nests of other species because they are incapable of raising their own young, or non-obligate brood parasites, which sometimes lay eggs in the nests of conspecifics to increase their reproductive output even though they could have raised their own young.[246] One hundred bird species, including honeyguides, icterids, and ducks, are obligate parasites, though the most famous are the cuckoos.[245] Some brood parasites are adapted to hatch before their host's young, which allows them to destroy the host's eggs by pushing them out of the nest or to kill the host's chicks; this ensures that all food brought to the nest will be fed to the parasitic chicks.[247]

Sexual selection

The peacock tail in flight, the classic example of a Fisherian runaway
Main article: Sexual selection in birds
Birds have evolved a variety of mating behaviours, with the peacock tail being perhaps the most famous example of sexual selection and the Fisherian runaway. Commonly occurring sexual dimorphisms such as size and colour differences are energetically costly attributes that signal competitive breeding situations.[248] Many types of avian sexual selection have been identified; intersexual selection, also known as female choice; and intrasexual competition, where individuals of the more abundant sex compete with each other for the privilege to mate. Sexually selected traits often evolve to become more pronounced in competitive breeding situations until the trait begins to limit the individual's fitness. Conflicts between an individual fitness and signalling adaptations ensure that sexually selected ornaments such as plumage colouration and courtship behaviour are "honest" traits. Signals must be costly to ensure that only good-quality individuals can present these exaggerated sexual ornaments and behaviours.[249]

Inbreeding depression

Main article: Inbreeding depression
Inbreeding causes early death (inbreeding depression) in the zebra finch Taeniopygia guttata.[250] Embryo survival (that is, hatching success of fertile eggs) was significantly lower for sib-sib mating pairs than for unrelated pairs.[251]
Darwin's finch Geospiza scandens experiences inbreeding depression (reduced survival of offspring) and the magnitude of this effect is influenced by environmental conditions such as low food availability.[252]

Inbreeding avoidance

Main article: Inbreeding avoidance
Incestuous matings by the purple-crowned fairy wren Malurus coronatus result in severe fitness costs due to inbreeding depression (greater than 30% reduction in hatchability of eggs).[253] Females paired with related males may undertake extra pair matings (see Promiscuity#Other animals for 90% frequency in avian species) that can reduce the negative effects of inbreeding. However, there are ecological and demographic constraints on extra pair matings. Nevertheless, 43% of broods produced by incestuously paired females contained extra pair young.[253]
Inbreeding depression occurs in the great tit (Parus major) when the offspring produced as a result of a mating between close relatives show reduced fitness. In natural populations of Parus major, inbreeding is avoided by dispersal of individuals from their birthplace, which reduces the chance of mating with a close relative.[254]
Southern pied babblers Turdoides bicolor appear to avoid inbreeding in two ways. The first is through dispersal, and the second is by avoiding familiar group members as mates.[255]
Cooperative breeding in birds typically occurs when offspring, usually males, delay dispersal from their natal group in order to remain with the family to help rear younger kin.[256] Female offspring rarely stay at home, dispersing over distances that allow them to breed independently, or to join unrelated groups. In general, inbreeding is avoided because it leads to a reduction in progeny fitness (inbreeding depression) due largely to the homozygous expression of deleterious recessive alleles.[257] Cross-fertilisation between unrelated individuals ordinarily leads to the masking of deleterious recessive alleles in progeny.[258][259]

Ecology

Gran Canaria blue chaffinch, an example of a bird highly specialised in its habitat, in this case in the Canarian pine forests
Birds occupy a wide range of ecological positions.[192] While some birds are generalists, others are highly specialised in their habitat or food requirements. Even within a single habitat, such as a forest, the niches occupied by different species of birds vary, with some species feeding in the forest canopy, others beneath the canopy, and still others on the forest floor. Forest birds may be insectivores, frugivores, or nectarivores. Aquatic birds generally feed by fishing, plant eating, and piracy or kleptoparasitism. Many grassland birds are granivores. Birds of prey specialise in hunting mammals or other birds, while vultures are specialised scavengers. Birds are also preyed upon by a range of mammals including a few avivorous bats.[260] A wide range of endo- and ectoparasites depend on birds and some parasites that are transmitted from parent to young have co-evolved and show host-specificity.[261]
Some nectar-feeding birds are important pollinators, and many frugivores play a key role in seed dispersal.[262] Plants and pollinating birds often coevolve,[263] and in some cases a flower's primary pollinator is the only species capable of reaching its nectar.[264]
Birds are often important to island ecology. Birds have frequently reached islands that mammals have not; on those islands, birds may fulfil ecological roles typically played by larger animals. For example, in New Zealand nine species of moa were important browsers, as are the kererū and kokako today.[262] Today the plants of New Zealand retain the defensive adaptations evolved to protect them from the extinct moa.[265]
Many birds act as ecosystem engineers through the construction of nests, which provide important microhabitats and food for hundreds of species of invertebrates.[266][267] Nesting seabirds may affect the ecology of islands and surrounding seas, principally through the concentration of large quantities of guano, which may enrich the local soil[268] and the surrounding seas.[269]
A wide variety of avian ecology field methods, including counts, nest monitoring, and capturing and marking, are used for researching avian ecology.[270]

Relationship with humans

Main article: Human uses of birds
Industrial farming of chickens
Since birds are highly visible and common animals, humans have had a relationship with them since the dawn of man.[271] Sometimes, these relationships are mutualistic, like the cooperative honey-gathering among honeyguides and African peoples such as the Borana.[272] Other times, they may be commensal, as when species such as the house sparrow[273] have benefited from human activities. Several bird species have become commercially significant agricultural pests,[274] and some pose an aviation hazard.[275] Human activities can also be detrimental, and have threatened numerous bird species with extinction (hunting, avian lead poisoning, pesticides, roadkill, wind turbine kills[276] and predation by pet cats and dogs are common causes of death for birds).[277]
Birds can act as vectors for spreading diseases such as psittacosis, salmonellosis, campylobacteriosis, mycobacteriosis (avian tuberculosis), avian influenza (bird flu), giardiasis, and cryptosporidiosis over long distances. Some of these are zoonotic diseases that can also be transmitted to humans.[278]

Economic importance

See also: Pet § Birds
The use of cormorants by Asian fishermen is in steep decline but survives in some areas as a tourist attraction.
Domesticated birds raised for meat and eggs, called poultry, are the largest source of animal protein eaten by humans; in 2003, 76 million tons of poultry and 61 million tons of eggs were produced worldwide.[279] Chickens account for much of human poultry consumption, though domesticated turkeys, ducks, and geese are also relatively common.[280] Many species of birds are also hunted for meat. Bird hunting is primarily a recreational activity except in extremely undeveloped areas. The most important birds hunted in North and South America are waterfowl; other widely hunted birds include pheasants, wild turkeys, quail, doves, partridge, grouse, snipe, and woodcock.[citation needed] Muttonbirding is also popular in Australia and New Zealand.[281] Although some hunting, such as that of muttonbirds, may be sustainable, hunting has led to the extinction or endangerment of dozens of species.[282]
Other commercially valuable products from birds include feathers (especially the down of geese and ducks), which are used as insulation in clothing and bedding, and seabird faeces (guano), which is a valuable source of phosphorus and nitrogen. The War of the Pacific, sometimes called the Guano War, was fought in part over the control of guano deposits.[283]
Birds have been domesticated by humans both as pets and for practical purposes. Colourful birds, such as parrots and mynas, are bred in captivity or kept as pets, a practice that has led to the illegal trafficking of some endangered species.[284] Falcons and cormorants have long been used for hunting and fishing, respectively. Messenger pigeons, used since at least 1 AD, remained important as recently as World War II. Today, such activities are more common either as hobbies, for entertainment and tourism,[285]
Amateur bird enthusiasts (called birdwatchers, twitchers or, more commonly, birders) number in the millions.[286] Many homeowners erect bird feeders near their homes to attract various species. Bird feeding has grown into a multimillion-dollar industry; for example, an estimated 75% of households in Britain provide food for birds at some point during the winter.[287]

In religion and mythology

The 3 of Birds by the Master of the Playing Cards, 15th-century Germany
Birds play prominent and diverse roles in religion and mythology. In religion, birds may serve as either messengers or priests and leaders for a deity, such as in the Cult of Makemake, in which the Tangata manu of Easter Island served as chiefs[288] or as attendants, as in the case of Hugin and Munin, the two common ravens who whispered news into the ears of the Norse god Odin. In several civilisations of ancient Italy, particularly Etruscan and Roman religion, priests were involved in augury, or interpreting the words of birds while the "auspex" (from which the word "auspicious" is derived) watched their activities to foretell events.[289]
They may also serve as religious symbols, as when Jonah (Hebrew: יונה, dove) embodied the fright, passivity, mourning, and beauty traditionally associated with doves.[290] Birds have themselves been deified, as in the case of the common peacock, which is perceived as Mother Earth by the people of southern India.[291] In the ancient world, doves were used as symbols of the Mesopotamian goddess Inanna (later known as Ishtar),[292][293] the Canaanite mother goddess Asherah,[292][293][294] and the Greek goddess Aphrodite.[292][293][295][296][297] In ancient Greece, Athena, the goddess of wisdom and patron deity of the city of Athens, had a little owl as her symbol.[298][299][300] In religious images preserved from the Inca and Tiwanaku empires, birds are depicted in the process of transgressing boundaries between earthly and underground spiritual realms.[301] Indigenous peoples of the central Andes maintain legends of birds passing to and from metaphysical worlds.[301]

In culture and folklore

Further information: Birds in Meitei culture
Painted tiles with design of birds from Qajar dynasty
Birds have featured in culture and art since prehistoric times, when they were represented in early cave painting[302] and carvings.[303] Some birds have been perceived as monsters, including the mythological Roc and the Māori's legendary Pouākai, a giant bird capable of snatching humans.[304] Birds were later used as symbols of power, as in the magnificent Peacock Throne of the Mughal and Persian emperors.[305] With the advent of scientific interest in birds, many paintings of birds were commissioned for books.[citation needed]
Among the most famous of these bird artists was John James Audubon, whose paintings of North American birds were a great commercial success in Europe and who later lent his name to the National Audubon Society.[306] Birds are also important figures in poetry; for example, Homer incorporated nightingales into his Odyssey, and Catullus used a sparrow as an erotic symbol in his Catullus 2.[307] The relationship between an albatross and a sailor is the central theme of Samuel Taylor Coleridge's The Rime of the Ancient Mariner, which led to the use of the term as a metaphor for a 'burden'.[308] Other English metaphors derive from birds; vulture funds and vulture investors, for instance, take their name from the scavenging vulture.[309] Aircraft, particularly military aircraft, are frequently named after birds. The predatory nature of raptors make them popular choices for fighter aircraft such as the F-16 Fighting Falcon and the Harrier Jump Jet, while the names of seabirds may be chosen for aircraft primarily used by naval forces such as the HU-16 Albatross and the V-22 Osprey.[310]
The flag of Dominica prominently features the Sisserou Parrot, its national bird.
Perceptions of bird species vary across cultures. Owls are associated with bad luck, witchcraft, and death in parts of Africa,[311] but are regarded as wise across much of Europe.[312] Hoopoes were considered sacred in Ancient Egypt and symbols of virtue in Persia, but were thought of as thieves across much of Europe and harbingers of war in Scandinavia.[313] In heraldry, birds, especially eagles, often appear in coats of arms[314] In vexillology, birds are a popular choice on flags. Birds feature in the flag designs of 17 countries and numerous subnational entities and territories.[315] Birds are used by nations to symbolize a country's identity and heritage, with 91 countries officially recognizing a national bird. Birds of prey are highly represented, though some nations have chosen other species of birds with parrots being popular among smaller, tropical nations.[316]

In music

Main article: Birds in music
In music, birdsong has influenced composers and musicians in several ways: they can be inspired by birdsong; they can intentionally imitate bird song in a composition, as Vivaldi, Messiaen, and Beethoven did, along with many later composers; they can incorporate recordings of birds into their works, as Ottorino Respighi first did; or like Beatrice Harrison and David Rothenberg, they can duet with birds.[317][318][319][320]
A 2023 archaeological excavation of a 10000-year-old site in Israel yielded hollow wing bones of coots and ducks with perforations made on the side that are thought to have allowed them to be used as flutes or whistles possibly used by Natufian people to lure birds of prey.[321]

Threats and conservation

Main article: Bird conservation
See also: Late Quaternary prehistoric birds, List of extinct birds, and Raptor conservation
The California condor once numbered only 22 birds, but conservation measures have raised that to over 500 today.
Human activities have caused population decreases or extinction in many bird species. Over a hundred bird species have gone extinct in historical times,[322] although the most dramatic human-caused avian extinctions, eradicating an estimated 750–1800 species, occurred during the human colonisation of Melanesian, Polynesian, and Micronesian islands.[323] Many bird populations are declining worldwide, with 1,227 species listed as threatened by BirdLife International and the IUCN in 2009.[324][325]
The most commonly cited human threat to birds is habitat loss.[326] Other threats include overhunting, accidental mortality due to collisions with buildings or vehicles, long-line fishing bycatch,[327] pollution (including oil spills and pesticide use),[328] competition and predation from nonnative invasive species,[329] and climate change.
Governments and conservation groups work to protect birds, either by passing laws that preserve and restore bird habitat or by establishing captive populations for reintroductions. Such projects have produced some successes; one study estimated that conservation efforts saved 16 species of bird that would otherwise have gone extinct between 1994 and 2004, including the California condor and Norfolk parakeet.[330]
Human activities have allowed the expansion of only a few species, such as the barn swallow and European starling.

See also

• Avian sleep
• Biodiversity loss
• Climate change and birds
• Glossary of bird terms
• List of individual birds
• Ornithology

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