Roof tiles are designed to keep out rain, are traditionally made from locally available materials such as terracotta or slate. Modern materials such as concrete and plastic are used and some clay tiles have a waterproof glaze. Roof tiles are'hung' from the framework of a roof by fixing them with nails; the tiles are hung in parallel rows, with each row overlapping the row below it to exclude rainwater and to cover the nails that hold the row below. There are roof tiles for special positions where the planes of the several pitches meet, they include ridge and valley tiles. These can either be pointed in cement mortar or mechanically fixed. To roof tiling, tiling has been used to provide a protective weather envelope to the sides of timber frame buildings; these are hung on laths nailed to wall timbers, with tiles specially molded to cover corners and jambs. These tiles are shaped at the exposed end to give a decorative effect. Another form of this is the so-called mathematical tile, hung on laths and grouted.
This form of tiling gives an imitation of brickwork and was developed to give the appearance of brick, but avoided the brick taxes of the 18th century. Slate roof tiles were traditional in some areas near sources of supply, gave thin and light tiles when the slate was split into its natural layers, it is no longer a cheap material, is now less common. A large number of shapes of roof tiles have evolved; these include: Flat tiles -- the simplest type. An example of this is the clay-made "beaver-tail" tile, common in Southern Germany. Flat roof tiles are made of clay but may be made of stone, plastic, concrete, or solar cells. Imbrex and tegula – an ancient Roman pattern of curved and flat tiles that make rain channels on a roof. Roman tiles – flat in the middle, with a concave curve at one end and a convex curve at the other, to allow interlocking. Pantiles – with an S-shaped profile, allowing adjacent tiles to interlock; these result in a ridged pattern resembling a ploughed field. An example of this is the "double Roman" tile, dating from the late 19th century in England and US.
Monk and Nun tiles called mission or barrel tiles – semi-cylindrical tiles laid in alternating columns of convex and concave tiles. They were made by forming clay around a curved surface a log or the maker's thigh. Today barrel tiles are mass-produced from clay, concrete or plastic. Interlocking roof tiles – similar to pantiles with side and top locking to improve protection from water and wind. Antefixes – vertical blocks which terminate the covering tiles of a tiled roof. Tiled roofs first replaced thatched roofs in ancient Mesopotamia. Fired roof-tiles occur from as early as the 3rd millennium BC in the Early Helladic House of the tiles in Lerna, Greece. Debris found at the site contained thousands of terracotta tiles. In the Mycenaean period, roof tiles are documented for Midea; the earliest finds of roof tiles in archaic Greece are documented from a restricted area around Corinth, where fired tiles began to replace thatched roofs at two temples of Apollo and Poseidon between 700 and 650 BC.
Spreading roof tiles were within fifty years in evidence at a large number of sites around the Eastern Mediterranean, including Mainland Greece, Western Asia Minor, Southern and Central Italy. Early roof-tiles showed an S-shape, with the cover tile forming one piece, they were rather bulky affairs, weighing around 30 kg apiece - more expensive and labour-intensive to produce than thatch. Their introduction has been explained by their enhanced fire-resistance, which gave desired protection to the costly temples; the spread of the roof-tile technique has to be viewed in connection with the simultaneous rise of monumental architecture in ancient Greece. Only the newly appearing stone walls, which were replacing the earlier mudbrick and wood walls, were strong enough to support the weight of a tiled roof; as a side-effect, it has been assumed that the new stone and tile construction ushered in the end of'Chinese roof' construction in Greek architecture, as they made the need for an extended roof as rain protection for the mudbrick walls obsolete.
Production of Dutch roof tiles started in the 14th century when city rulers required the use of fireproof materials. At the time, most houses were made of wood and had thatch roofing, which would cause fires to spread quickly. To satisfy demand, many small roof-tile makers began to produce roof tiles by hand. Many of these small factories were built near rivers where there was a ready source of clay and cheap transport. Tilehanging or vertical tiling is the construction of a building with roof tiles hung vertically on the sides of the building, it is a popular style used in neo-vernacular architecture in Britain. In China, roof tiles are in use throughout the country on temples and village houses. Both imbrex and tegula and mission tiles are used. Temples use glazed ornate tiles and antefixes; the most common traditional colour is orange-yellow. Old buildings have simple, clay tiles that have been fired in a kiln. Tiled roofs, while once ubiquitous in China, are now used less. One reason for this is that the majority of new houses and apartment buildings in China are built with flat roofs.
Dow Chemical Company began producing solar roof tiles in 2005, several other manufacturers followed suit. They are similar in design to conventional roof tiles but with a photovoltaic cell within in order to generate renewable electricity. A collaboration between the companies SolarCity and Tesla produced
Peafowl is a common name for three species of birds in the genera Pavo and Afropavo of the Phasianidae family, the pheasants and their allies. Male peafowl are referred to as peacocks, female peafowl as peahens; the two Asiatic species are the blue or Indian peafowl of the Indian subcontinent, the green peafowl of Southeast Asia. Male peafowl are known for their extravagant plumage; the latter is prominent in the Asiatic species, which have an eye-spotted "tail" or "train" of covert feathers, which they display as part of a courtship ritual. The functions of the elaborate iridescent colouration and large "train" of peacocks have been the subject of extensive scientific debate. Charles Darwin suggested they served to attract females, the showy features of the males had evolved by sexual selection. More Amotz Zahavi proposed in his handicap theory that these features acted as honest signals of the males' fitness, since less-fit males would be disadvantaged by the difficulty of surviving with such large and conspicuous structures.
The Indian peacock has iridescent blue and green plumage metallic blue and green, but the green peacock has green and bronze body feathers. In both species, females lack the train and the head ornament; the peacock "tail", known as a "train", consists not of tail quill feathers, but elongated upper tail coverts. These feathers are marked with best seen when a peacock fans his tail. Both sexes of all species have a crest atop the head; the Indian peahen has a mixture of dull grey and green in her plumage. The female displays her plumage to ward off female competition or signal danger to her young. Green peafowl differ from Indian peafowl in that the male has green and gold plumage and black wings with a sheen of blue. Unlike Indian peafowl, the green peahen is similar to the male, only having shorter upper tail coverts, a more coppery neck, overall less iridescence; the Congo peacock male does not display his covert feathers, but uses his actual tail feathers during courtship displays. These feathers are much shorter than those of the Indian and green species, the ocelli are much less pronounced.
Females of the Indian and African species brown. Chicks of both sexes in all the species are cryptically coloured, they vary between yellow and tawny with patches of darker brown or light tan and "dirty white" ivory. Hybrids between Indian and Green peafowl are called Spaldings, after the first person to hybridize them, Mrs. Keith Spalding. Unlike many hybrids, spaldings are fertile and benefit from hybrid vigor. Plumage varies between individual spaldings, with some looking far more like green peafowl and some looking far more like blue peafowl, though most visually carry traits of both. In addition to the wild-type "blue" colouration, several hundred variations in colour and pattern are recognized as separate morphs of the Indian Blue among peafowl breeders. Pattern variations include solid-wing/black shoulder, white-eye, silver pied. colour variations include white, Buford bronze, midnight, charcoal and taupe, as well as the sex-linked colours purple, cameo and Sonja's Violeta. Additional colour and pattern variations are first approved by the United Peafowl Association to become recognized as a morph among breeders.
Alternately-coloured peafowl are born differently coloured than wild-type peafowl, though each colour is recognizable at hatch, their peachick plumage does not match their adult plumage. Peafowl appear with white plumage. Although albino peafowl do exist, this is quite rare, all white peafowl are not albinos. Leucistic peafowl can produce pigment but not deposit the pigment to their feathers; this results in the complete lack of colouration in their blue-grey eye colour. Pied peafowl are affected by partial leucism, where only some pigment cells fail to migrate, resulting in birds that have colour but have patches absent of all colour. By contrast, true albino peafowl would have a complete lack of melanin, resulting in irises that look red or pink. Leucistic peachicks are born yellow and become white as they mature; as with many birds, vibrant iridescent plumage colours are not pigments, but structural colouration. Optical interference Bragg reflections, based on regular, periodic nanostructures of the barbules of the feathers, produce the peacock's colours.
Slight changes to the spacing of these barbules result in different colours. Brown feathers are a mixture of red and blue: one colour is created by the periodic structure and the other is created by a Fabry–Pérot interference peak from reflections from the outer and inner boundaries; such structural colouration causes the iridescence of the peacock's hues. Interference effects depend on light angle rather than actual pigments. Charles Darwin suggested in On the Origin of Species that the peafowl's plumage had evolved through sexual selection, he expanded upon The Descent of Man and Selection in Relation to Sex. The sexual struggle is of two kinds.
The alula, or bastard wing, is a small projection on the anterior edge of the wing of modern birds and a few non-avian dinosaurs. The word is Latin and means "winglet"; the alula is the moving first digit, a bird's "thumb", bears three to five small flight feathers, with the exact number depending on the species. There are minor covert feathers overlying the flight feathers. Like the larger flight feathers found on the wing's trailing edge, these alula feathers are asymmetrical, with the shaft running closer to anterior edge. In most situations, the alula is held flush against the wing; when flying at slow speeds or landing, the bird moves its alula upwards and forward, which creates a small slot on the wing's leading edge. This functions in the same way as the slats on the wing of an aircraft, allowing the wing to achieve a higher than normal angle of attack – and thus lift – without resulting in a stall; the tip of the alula forms a tiny vortex. During stretching of the wing down toward the ground, the alula is abducted from the wing and can be viewed.
In falcons, the alula is more prominent, provides a degree of control when the wing is cupped or tucked in a dive/stoop. The Alulae are notable in Peregrine falcons; the presence of an alula has been confirmed in several now-extinct ancient relatives of modern birds, including Eoalulavis hoyasi and the earlier Protopteryx fengningensis. Since these species are not related to modern birds, either the alula evolved twice, or it did so more than 130 million years ago. Bird flight Alular digit homology Leading edge slot, the man-made equivalent on fixed-wing aircraft Ehrlich, Paul R; the Birdwatcher's Handbook, Oxford University Press, ISBN 0-19-858407-5 Sanz, J. L.. "An Early Cretaceous bird from Spain and its implications for the evolution of avian flight", Nature, 382: 442–445, doi:10.1038/382442a0 Zhang, Fucheng.
Birds known as Aves, are a group of endothermic vertebrates, characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, a strong yet lightweight skeleton. Birds range in size from the 5 cm bee hummingbird to the 2.75 m ostrich. They rank as the world's most numerically-successful class of tetrapods, with ten thousand living species, more than half of these being passerines, sometimes known as perching birds. Birds have wings which are less developed depending on the species. Wings, which evolved from forelimbs, gave birds the ability to fly, although further evolution has led to the loss of flight in flightless birds, including ratites and diverse endemic island species of birds; the digestive and respiratory systems of birds are uniquely adapted for flight. Some bird species of aquatic environments seabirds and some waterbirds, have further evolved for swimming; the fossil record demonstrates that birds are modern feathered dinosaurs, having evolved from earlier feathered dinosaurs within the theropod group, which are traditionally placed within the saurischian dinosaurs.
The closest living relatives of birds are the crocodilians. Primitive bird-like dinosaurs that lie outside class Aves proper, in the broader group Avialae, have been found dating back to the mid-Jurassic period, around 170 million years ago. Many of these early "stem-birds", such as Archaeopteryx, were not yet capable of powered flight, many retained primitive characteristics like toothy jaws in place of beaks, long bony tails. DNA-based evidence finds that birds diversified around the time of the Cretaceous–Palaeogene extinction event 66 million years ago, which killed off the pterosaurs and all the non-avian dinosaur lineages, but birds those in the southern continents, survived this event and migrated to other parts of the world while diversifying during periods of global cooling. This makes them the sole surviving dinosaurs according to cladistics; some birds corvids and parrots, are among the most intelligent animals. Many species annually migrate great distances. Birds are social, communicating with visual signals and bird songs, participating in such social behaviours as cooperative breeding and hunting and mobbing of predators.
The vast majority of bird species are monogamous for one breeding season at a time, sometimes for years, but for life. Other species have breeding systems that are polygynous or polyandrous. Birds produce offspring by laying eggs, they are 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 when not fertilised, though unfertilised eggs do not produce offspring. 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 and feathers. Songbirds and other species are popular as pets. Guano is harvested for use as a fertiliser. Birds prominently figure throughout human culture. About 120–130 species have become extinct due to human activity since the 17th century, 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 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 in use. Birds are categorised as the biological class Aves in Linnaean taxonomy. Phylogenetic taxonomy places Aves in the dinosaur clade Theropoda. Aves and a sister group, the clade Crocodilia, contain the only living representatives of the reptile clade Archosauria. During the late 1990s, Aves was most 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, is used by many scientists including adherents of the Phylocode system. 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, assigning them, instead, to the Avialae, in part to avoid the uncertainties about the placement of Archaeopteryx in relation to animals traditionally thought of as theropod dinosaurs.
Gauthier identified four different definitions for the same biological name "Aves", a problem. Gauthier 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, he assigned other names to the other groups. Aves can mean all archosaurs closer to birds than to crocodiles Aves can mean those advanced archosaurs with feathers Aves can mean those feathered dinosaurs that fly Aves can mean the last common ancestor of all the living birds and all of its descendants (a "c
The eye-ring of a bird is a ring of tiny feathers that surrounds the orbital ring, a ring of bare skin surrounding a bird's eye. The eye-ring is decorative, its colour may contrast with adjoining plumage; the ring of feathers is sometimes incomplete. In the absence of a conspicuous eye-ring, the orbital ring of a bird is referred to as the eye-ring; the bare orbital ring may form an eye-wattle. These are useful field marks in many bird species, the eye-ringed flatbill, eye-ringed tody-tyrant and eye-ringed thistletail are examples of species named for either of these. Eye-rings are believed to convey various types of signals between individual birds; some eye-rings appear only at sexual maturity, while others suggest the individual's age or health status. Individual birds may be included or excluded from reproductive capability due to signals conveyed by the eye-ring. Red carotenoid-based colors of the orbital rings of pheasants are known to be related to health; the function of the white eye-rings in white-eyes is unknown.
It is suspected that they may serve to highlight infestations of small ectoparasites around the eyes. Untainted white eye-rings may express vigorous health. In addition they may signal membership of a particular group or population, as different species and populations may have rings of differing colour, shape or completeness; these recognition signals could play a role in reproductive isolation and speciation. Glossary of bird terms Iris List of terms used in bird topography Sclerotic eye-ring
Flight feathers are the long, asymmetrically shaped, but symmetrically paired pennaceous feathers on the wings or tail of a bird. The primary function of the flight feathers is to aid in the generation of both thrust and lift, thereby enabling flight; the flight feathers of some birds have evolved to perform additional functions associated with territorial displays, courtship rituals or feeding methods. In some species, these feathers have developed into long showy plumes used in visual courtship displays, while in others they create a sound during display flights. Tiny serrations on the leading edge of their remiges help owls to fly silently, while the extra-stiff rectrices of woodpeckers help them to brace against tree trunks as they hammer on them. Flightless birds still retain flight feathers, though sometimes in radically modified forms; the moult of their flight feathers can cause serious problems for birds, as it can impair their ability to fly. Different species have evolved different strategies for coping with this, ranging from dropping all their flight feathers at once to extending the moult over a period of several years.
Remiges are located on the posterior side of the wing. Ligaments attach the long calami to the wing bones, a thick, strong band of tendinous tissue known as the postpatagium helps to hold and support the remiges in place. Corresponding remiges on individual birds are symmetrical between the two wings, matching to a large extent in size and shape, though not in pattern, they are given different names depending on their position along the wing. Primaries are connected to the manus; these feathers are important for flapping flight, as they are the principal source of thrust, moving the bird forward through the air. The mechanical properties of primaries are important in supporting flight. Most thrust is generated on the downstroke of flapping flight. However, on the upstroke, the primaries are separated and rotated, reducing air resistance while still helping to provide some thrust; the flexibility of the remiges on the wingtips of large soaring birds allows for the spreading of those feathers, which helps to reduce the creation of wingtip vortices, thereby reducing drag.
The barbules on these feathers, friction barbules, are specialized with large lobular barbicels that help grip and prevent slippage of overlying feathers and are present in most of the flying birds. Species vary somewhat in the number of primaries they possess; the number in non-passerines varies between 9 and 11, but grebes and flamingos have 12, ostriches have 16. While most modern passerines have ten primaries, some have only nine; those with nine are missing the most distal primary, very small and sometimes rudimentary in passerines. The outermost primaries—those connected to the phalanges—are sometimes known as pinions. Secondaries are connected to the ulna. In some species, the ligaments that bind these remiges to the bone connect to small, rounded projections, known as quill knobs, on the ulna. Secondary feathers remain close together in flight and help to provide lift by creating the airfoil shape of the bird's wing. Secondaries tend to be shorter and broader with blunter ends, they vary in number from 6 in hummingbirds to as many as 40 in some species of albatross.
In general and longer-winged species have a larger number of secondaries. Birds in more than 40 non-passerine families seem to be missing the fifth secondary feather on each wing, a state known as diastataxis. In these birds, the fifth set of secondary covert feathers does not cover any remiges due to a twisting of the feather papillae during embryonic development. Loons, pelicans and eagles, sandpipers, gulls and owls are among the families missing this feather. Tertials arise in the brachial region and are not considered true remiges as they are not supported by attachment to the corresponding bone, in this case the humerus; these elongated "true" tertials act as a protective cover for all or part of the folded primaries and secondaries, do not qualify as flight feathers as such. However, many authorities use the term tertials to refer to the shorter, more symmetrical innermost secondaries of passerines in an effort to distinguish them from other secondaries; the term humeral is sometimes used for birds such as the albatrosses and pelicans that have a long humerus.
The calami of the flight feathers are protected by a layer of non-flight feathers called covert feathers or tectrices, at least one layer of them both above and beneath the flight feathers of the wings as well as above and below the rectrices of the tail. These feathers may vary in size — in fact, the upper tail tectrices of the male peafowl, rather than its rectrices, are what constitute its elaborate and colorful "train"; the outermost primaries of large soaring birds ra
The supercilium is a plumage feature found on the heads of some bird species. It is a stripe which runs from the base of the bird's beak above its eye, finishing somewhere towards the rear of the bird's head. Known as an "eyebrow", it is distinct from the eyestripe, a line which runs across the lores, continues behind the eye. Where a stripe is present only above the lores, does not continue behind the eye, it is called a supraloral stripe or supraloral. On most species which display a supercilium, it is paler than the adjacent feather tracts; the colour, shape or other features of the supercilium can be useful in bird identification. For example, the supercilium of the dusky warbler, an Old World warbler species, can be used to distinguish it from the similar Radde's warbler; the dusky warbler's supercilium is demarcated and narrow in front of the eye, becoming broader and more buffy towards the rear, whereas that of the Radde's warbler is diffusely defined and broadest in front of the eye, becoming narrower and more whitish toward the rear.
The supercilium of the northern waterthrush, a New World warbler, differs subtly from that of the related Louisiana waterthrush. The Louisiana has a bicoloured supercilium which widens behind the eye, while the northern has an evenly buffy eyebrow, either the same width throughout or narrower behind the eye. A split supercilium divides above the lores. In some species, such as the jack snipe, the divided stripes reconnect again behind the eye. In others, such as the broad-billed sandpiper, the divided stripes remain separate. A supercilium drop is a feature found on some pipits. Dunn, Jon L.. Field Guide to the Birds of North America. Washington, D. C.: National Geographic Society. ISBN 0-7922-5314-0. Hayman, Peter. Shorebirds. Breckenham, UK: Croom Helm. ISBN 0-7099-2034-2