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42-479: A covert feather or tectrix on a bird is one of a set of feathers , called coverts (or tectrices ), which cover other feathers. The coverts help to smooth airflow over the wings and tail. The ear coverts are small feathers behind the bird's eye which cover the ear opening (the ear of a bird has no external features). The uppertail and undertail coverts cover the base of the tail feathers above and below. Sometimes these coverts are more specialised. The "tail" of

84-454: A peacock is made of elongated uppertail coverts. The upperwing coverts fall into two groups: those on the inner wing, which overlay the secondary flight feathers , known as the secondary coverts, and those on the outer wing, which overlay the primary flight feathers , the primary coverts. Within each group, the feathers form a number of rows. The feathers of the outermost, largest, row are termed greater (primary-/secondary-) coverts; those in

126-1242: A phylogenetic tree of the Neoptera (note that many non-subsocial groups are omitted): Embioptera (webspinners) Blattodea (cockroaches, inc. eusocial termites ) Mantodea (mantises) Orthoptera (grasshoppers, crickets) Dermaptera (earwigs) Zoraptera (angel insects) Thysanoptera (thrips) Membracidae (treehoppers, thorn bugs) Pentatomidae (shield bugs) Reduviidae (predatory bugs) Tingidae (lace bugs) Psocoptera (bark lice) Staphylinidae (rove beetles) Silphidae (carrion beetles) Passalidae (bessbugs) Scarabaeidae (scarabs) Tenebrionidae (leaf/flower beetles) Erotylidae (pleasing fungus beetles) Chrysomelidae (leaf beetles) Raphidioptera (snakeflies) Neuroptera (lacewings, alderflies, and allies) Antliophora (true flies, scorpionflies, fleas) Trichoptera (caddisflies) Lepidoptera (butterflies and moths) Hymenoptera (sawflies, wasps, ants, bees) (apart from eusocial species) Solitary-but-social animals forage separately, but some individuals sleep in

168-695: A better sense of smell. A third stage of bird evolution starting with Ornithothoraces (the "bird-chested" avialans) can be associated with the refining of aerodynamics and flight capabilities, and the loss or co-ossification of several skeletal features. Particularly significant are the development of an enlarged, keeled sternum and the alula , and the loss of grasping hands. † Anchiornis † Archaeopteryx † Xiaotingia † Rahonavis † Jeholornis † Jixiangornis † Balaur † Zhongjianornis † Sapeornis † Confuciusornithiformes † Protopteryx † Pengornis Ornithothoraces † Enantiornithes Social animal Sociality

210-453: A classification system for presociality in 1969, building on the earlier work of Suzanne Batra (who coined the words eusocial and quasisocial in 1966). Michener used these terms in his study of bees, but also saw a need for additional classifications: subsocial , communal , and semisocial . In his use of these words, he did not generalize beyond insects . E. O. Wilson later refined Batra's definition of quasisocial . Subsociality

252-473: A definition similar to "all theropods closer to birds than to Deinonychus ", with Troodon being sometimes added as a second external specifier in case it is closer to birds than to Deinonychus . Avialae is also occasionally defined as an apomorphy-based clade (that is, one based on physical characteristics). Jacques Gauthier , who named Avialae in 1986, re-defined it in 2001 as all dinosaurs that possessed feathered wings used in flapping flight , and

294-442: A group called Paraves . Some basal members of Deinonychosauria, such as Microraptor , have features which may have enabled them to glide or fly. The most basal deinonychosaurs were very small. This evidence raises the possibility that the ancestor of all paravians may have been arboreal , have been able to glide, or both. Unlike Archaeopteryx and the non-avialan feathered dinosaurs, who primarily ate meat, studies suggest that

336-439: A high metabolic rate, a four-chambered heart , and a strong yet lightweight skeleton . Birds live worldwide and range in size from the 5.5 cm (2.2 in) bee hummingbird to the 2.8 m (9 ft 2 in) common ostrich . There are over 11,000 living species and they are split into 44 orders . More than half are passerine or "perching" birds. Birds have wings whose development varies according to species;

378-562: A meta-class: the parasocial . The two commonalities of parasocial taxa are the exhibition of parental investment, and socialization in a single, cooperative dwelling . Communal, quasisocial, and semisocial groups differ in a few ways. In a communal group, adults cohabit in a single nest site, but they each care for their own young. Quasisocial animals cohabit, but they also share the responsibilities of brood care . (This has been observed in some Hymenoptera and spider taxa, as well as in some other invertebrates .) A semisocial population has

420-570: A single reproductive queen; they usually live in harsh or limiting environments. A study conducted by O'Riain and Faulkes in 2008 suggests that, due to regular inbreeding avoidance , mole rats sometimes outbreed and establish new colonies when resources are sufficient. Eusociality has arisen among some crustaceans that live in groups in a restricted area. Synalpheus regalis are snapping shrimp that rely on fortress defense. They live in groups of closely related individuals, amidst tropical reefs and sponges . Each group has one breeding female; she

462-406: A sister group, the order Crocodilia , contain the only living representatives of the reptile clade Archosauria . During the late 1990s, Aves was most commonly defined phylogenetically as all descendants of the most recent common ancestor of modern birds and Archaeopteryx lithographica . However, an earlier definition proposed by Jacques Gauthier gained wide currency in the 21st century, and

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504-512: A solitary but social behavior, that is, they live apart from their own species but interact with humans. This behavior has been observed in species including bottlenose dolphin , common dolphin , striped dolphin , beluga , Risso's dolphin , and orca . Notable individuals include Pelorus Jack (1888–1912), Tião (1994–1995), and Fungie (1983–2020). At least 32 solitary-sociable dolphins were recorded between 2008 and 2019. Sociobiologists place communal, quasisocial, and semisocial animals into

546-717: A time, sometimes for years, and rarely for life. Other species have breeding systems that are polygynous (one male with many females) or, rarely, polyandrous (one female with many males). Birds produce offspring by laying eggs which are fertilised through sexual reproduction . They are usually laid in a nest and incubated by the parents. Most birds have an extended period of parental care after hatching. Many species of birds are economically important as food for human consumption and raw material in manufacturing, with domesticated and undomesticated birds being important sources of eggs, meat, and feathers. Songbirds , parrots, and other species are popular as pets. Guano (bird excrement)

588-483: Is eusociality . A eusocial taxon is one that exhibits overlapping adult generations , reproductive division of labor , cooperative care of young, and—in the most refined cases—a biological caste system . One characteristic of social animals is the relatively high degree of cognitive ability. Social mammal predators such as spotted hyena and lion have been found to be better than non-social predators such as leopard and tiger at solving problems that require

630-436: Is a survival response to evolutionary pressures . For example, when a mother wasp stays near her larvae in the nest, parasites are less likely to eat the larvae. Biologists suspect that pressures from parasites and other predators selected this behavior in wasps of the family Vespidae . This wasp behaviour evidences the most fundamental characteristic of animal sociality: parental investment . Parental investment

672-462: Is a taxon's most social behaviour, then members of those populations are said to be solitary but social . See Wilson (1971) for definitions and further sub-classes of varieties of subsociality. Choe & Crespi (1997) and Costa (2006) give readable overviews. Subsociality is widely distributed among the winged insects, and has evolved independently many times. Insect groups that contain at least some subsocial species are shown in bold italics on

714-635: Is alive at the same time, and that the older generations also care for the newest offspring. Eusocial societies have overlapping adult generations, cooperative care of young, and division of reproductive labor. When organisms in a species are born with physical characteristics specific to a caste which never changes throughout their lives, this exemplifies the highest acknowledged degree of sociality. Eusociality has evolved in several orders of insects. Common examples of eusociality are from Hymenoptera ( ants , bees , sawflies , and wasps) and Blattodea (infraorder Isoptera , termites), but some Coleoptera (such as

756-471: Is any expenditure of resources (time, energy, social capital ) to benefit one's offspring . Parental investment detracts from a parent's capacity to invest in future reproduction and aid to kin (including other offspring). An animal that cares for its young but shows no other sociality traits is said to be subsocial . An animal that exhibits a high degree of sociality is called a social animal . The highest degree of sociality recognized by sociobiologists

798-533: Is called ornithology . Birds are feathered theropod dinosaurs and constitute the only known living dinosaurs . Likewise, birds are considered reptiles in the modern cladistic sense of the term, and their closest living relatives are the crocodilians . Birds are descendants of the primitive avialans (whose members include Archaeopteryx ) which first appeared during the Late Jurassic . According to recent estimates, modern birds ( Neornithes ) evolved in

840-409: Is common in the animal kingdom. In subsocial taxa , parents care for their young for some length of time. Even if the period of care is very short, the animal is still described as subsocial. If adult animals associate with other adults, they are not called subsocial, but are ranked in some other classification according to their social behaviours. If occasionally associating or nesting with other adults

882-429: Is harvested for use as a fertiliser. Birds figure throughout human culture. About 120 to 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. Recreational birdwatching is an important part of the ecotourism industry. The first classification of birds

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924-503: Is not considered a direct ancestor of birds, though it is possibly closely related to the true ancestor. Over 40% of key traits found in modern birds evolved during the 60 million year transition from the earliest bird-line archosaurs to the first maniraptoromorphs , i.e. the first dinosaurs closer to living birds than to Tyrannosaurus rex . The loss of osteoderms otherwise common in archosaurs and acquisition of primitive feathers might have occurred early during this phase. After

966-516: Is synonymous to Avifilopluma. † Scansoriopterygidae † Eosinopteryx † Jinfengopteryx † Aurornis † Dromaeosauridae † Troodontidae Avialae Based on fossil and biological evidence, most scientists accept that birds are a specialised subgroup of theropod dinosaurs and, more specifically, members of Maniraptora , a group of theropods which includes dromaeosaurids and oviraptorosaurs , among others. As scientists have discovered more theropods closely related to birds,

1008-530: Is used by many scientists including adherents to the PhyloCode . Gauthier defined Aves to include only the crown group of the set of modern birds. This was done by excluding most groups known only from fossils , and assigning them, instead, to the broader group Avialae, on the principle that a clade based on extant species should be limited to those extant species and their closest extinct relatives. Gauthier and de Queiroz identified four different definitions for

1050-715: The Late Cretaceous and diversified dramatically around the time of the Cretaceous–Paleogene extinction event 66 million years ago, which killed off the pterosaurs and all non- ornithuran dinosaurs. Many social species preserve knowledge across generations ( culture ). Birds are social, communicating with visual signals, calls, and songs , and participating in such behaviour as cooperative breeding and hunting, flocking , and mobbing of predators. The vast majority of bird species are socially (but not necessarily sexually) monogamous , usually for one breeding season at

1092-660: The Tiaojishan Formation of China, which has been dated to the late Jurassic period ( Oxfordian stage), about 160 million years ago. The avialan species from this time period include Anchiornis huxleyi , Xiaotingia zhengi , and Aurornis xui . The well-known probable early avialan, Archaeopteryx , dates from slightly later Jurassic rocks (about 155 million years old) from Germany . Many of these early avialans shared unusual anatomical features that may be ancestral to modern birds but were later lost during bird evolution. These features include enlarged claws on

1134-428: The appearance of Maniraptoromorpha, the next 40 million years marked a continuous reduction of body size and the accumulation of neotenic (juvenile-like) characteristics. Hypercarnivory became increasingly less common while braincases enlarged and forelimbs became longer. The integument evolved into complex, pennaceous feathers . The oldest known paravian (and probably the earliest avialan) fossils come from

1176-632: The beetle Austroplatypus incompertus ), Hemiptera (bugs such as Pemphigus spyrothecae ), and Thysanoptera (thrips) are described as eusocial. Eusocial species that lack this criterion of morphological caste differentiation are said to be primitively eusocial . Two potential examples of primitively eusocial mammals are the naked mole-rat and the Damaraland mole-rat ( Heterocephalus glaber and Fukomys damarensis , respectively). Both species are diploid and highly inbred , and they aid in raising their siblings and relatives, all of whom are born from

1218-509: The birds that descended from them. Despite being currently one of the most widely used, the crown-group definition of Aves has been criticised by some researchers. Lee and Spencer (1997) argued that, contrary to what Gauthier defended, this definition would not increase the stability of the clade and the exact content of Aves will always be uncertain because any defined clade (either crown or not) will have few synapomorphies distinguishing it from its closest relatives. Their alternative definition

1260-665: The earliest members of Aves, is removed from this group, becoming a non-avian dinosaur instead. These proposals have been adopted by many researchers in the field of palaeontology and bird evolution , though the exact definitions applied have been inconsistent. Avialae, initially proposed to replace the traditional fossil content of Aves, is often used synonymously with the vernacular term "bird" by these researchers. † Coelurus † Ornitholestes † Ornithomimosauria † Alvarezsauridae † Oviraptorosauria   Paraves Most researchers define Avialae as branch-based clade, though definitions vary. Many authors have used

1302-426: The features of communal and quasisocial populations, but they also have a biological caste system that delegates labor according to whether or not an individual is able to reproduce. Beyond parasociality is eusociality. Eusocial insect societies have all the characteristics of a semisocial one, except overlapping generations of adults cohabit and share in the care of young. This means that more than one adult generation

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1344-451: The first avialans were omnivores . The Late Jurassic Archaeopteryx is well known as one of the first transitional fossils to be found, and it provided support for the theory of evolution in the late 19th century. Archaeopteryx was the first fossil to display both clearly traditional reptilian characteristics—teeth, clawed fingers, and a long, lizard-like tail—as well as wings with flight feathers similar to those of modern birds. It

1386-418: The next row are the median (primary-/secondary-) coverts, and any remaining rows are termed lesser (primary-/secondary-) coverts. The underwing has corresponding sets of coverts (the names upperwing coverts and underwing coverts are used to distinguish the corresponding sets). In addition, the front edge of the wing is covered with a group of feathers called the marginal coverts. Within each group of wing coverts,

1428-523: The only known groups without wings are the extinct moa and elephant birds . Wings, which are modified forelimbs , gave birds the ability to fly, although further evolution has led to the loss of flight in some birds , including ratites , penguins , and diverse endemic island species. The digestive and respiratory systems of birds are also uniquely adapted for flight. Some bird species of aquatic environments, particularly seabirds and some waterbirds , have further evolved for swimming. The study of birds

1470-402: The outermost half) can be seen in the evolution of maniraptoromorphs, and this process culminated in the appearance of the pygostyle , an ossification of fused tail vertebrae. In the late Cretaceous, about 100 million years ago, the ancestors of all modern birds evolved a more open pelvis, allowing them to lay larger eggs compared to body size. Around 95 million years ago, they evolved

1512-528: The previously clear distinction between non-birds and birds has become blurred. By the 2000s, discoveries in the Liaoning Province of northeast China, which demonstrated many small theropod feathered dinosaurs , contributed to this ambiguity. The consensus view in contemporary palaeontology is that the flying theropods, or avialans , are the closest relatives of the deinonychosaurs , which include dromaeosaurids and troodontids . Together, these form

1554-417: The rows of feathers overlap each other like roof tiles (the greater coverts are overlain by the median coverts, which in turn are overlain by the outermost row of lesser coverts, and so on). Bird Birds are a group of warm-blooded vertebrates constituting the class Aves ( Latin: [ˈaveːs] ), characterised by feathers , toothless beaked jaws, the laying of hard-shelled eggs,

1596-452: The same biological name "Aves", which is a problem. The authors proposed to reserve the term Aves only for the crown group consisting of the last common ancestor of all living birds and all of its descendants, which corresponds to meaning number 4 below. They assigned other names to the other groups.   Lizards & snakes   Turtles   Crocodiles   Birds Under the fourth definition Archaeopteryx , traditionally considered one of

1638-517: The same location or share nests. The home ranges of females usually overlap, whereas those of males do not. Males usually do not associate with other males, and male offspring are usually evicted upon maturity. However, this is opposite among cassowaries , for example. Among primates , this form of social organization is most common among the nocturnal strepsirrhine species and tarsiers . Solitary-but-social species include mouse lemurs , lorises , and orangutans . Some individual cetaceans adopt

1680-545: The second toe which may have been held clear of the ground in life, and long feathers or "hind wings" covering the hind limbs and feet, which may have been used in aerial maneuvering. Avialans diversified into a wide variety of forms during the Cretaceous period. Many groups retained primitive characteristics , such as clawed wings and teeth, though the latter were lost independently in a number of avialan groups, including modern birds (Aves). Increasingly stiff tails (especially

1722-464: The use of innovation. Solitary animals such as the jaguar do not associate except for courtship and mating . If an animal taxon shows a degree of sociality beyond courtship and mating, but lacks any of the characteristics of eusociality, it is said to be presocial . Although presocial species are much more common than eusocial species, eusocial species have disproportionately large populations. The entomologist Charles D. Michener published

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1764-461: Was developed by Francis Willughby and John Ray in their 1676 volume Ornithologiae . Carl Linnaeus modified that work in 1758 to devise the taxonomic classification system currently in use. Birds are categorised as the biological class Aves in Linnaean taxonomy . Phylogenetic taxonomy places Aves in the clade Theropoda as an infraclass or a subclass, more recently a subclass. Aves and

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