Iridescence is the phenomenon of certain surfaces that appear to change colour as the angle of view or the angle of illumination changes. Examples of iridescence include soap bubbles, butterfly wings and seashells, as well as certain minerals, it is created by structural coloration. Pearlescence is a related effect where some or all of the reflected light is white, where iridescent effects produce only other colours; the term pearlescent is used to describe certain paint finishes in the automotive industry, which produce iridescent effects. The word iridescence is derived in part from the Greek word ἶρις îris, meaning rainbow, is combined with the Latin suffix -escent, meaning "having a tendency toward". Iris in turn derives from the goddess Iris of Greek mythology, the personification of the rainbow and acted as a messenger of the gods. Goniochromism is derived from the Greek words gonia, meaning "angle", chroma, meaning "colour". Iridescence is an optical phenomenon of surfaces in which hue changes with the angle of observation and the angle of illumination.
It is caused by multiple reflections from two or more semi-transparent surfaces in which phase shift and interference of the reflections modulates the incidental light. The thickness of the layers of the material determines the interference pattern. Iridescence can for example be due to thin-film interference, the functional analogue of selective wavelength attenuation as seen with the Fabry–Pérot interferometer, can be seen in oil films on water and soap bubbles. Iridescence is found in plants and many other items; the range of colours of natural iridescent objects can be narrow, for example shifting between two or three colours as the viewing angle changes, or a wide range of colours can be observed. Iridescence can be created by diffraction; this is found in items like DVDs, some types of prisms, or cloud iridescence. In the case of diffraction, the entire rainbow of colours will be observed as the viewing angle changes. In biology, this type of iridescence results from the formation of diffraction gratings on the surface, such as the long rows of cells in striated muscle, or the specialized abdominal scales of peacock spider Maratus robinsoni and M. chrysomelas.
Some types of flower petals can generate a diffraction grating, but the iridescence is not visible to humans and flower-visiting insects as the diffraction signal is masked by the coloration due to plant pigments. In biological uses, colours produced other than with pigments or dyes are called structural coloration. Microstructures multilayered, are used to produce bright but sometimes non-iridescent colours: quite elaborate arrangements are needed to avoid reflecting different colours in different directions. Structural coloration has been understood in general terms since Robert Hooke's 1665 book Micrographia, where Hooke noted that since the iridescence of a peacock's feather was lost when it was plunged into water, but reappeared when it was returned to the air, pigments could not be responsible, it was found that iridescence in the peacock is due to a complex photonic crystal. Pearlescence is an effect has a similar cause. Structures within a surface cause light to be reflected back, but in the case of pearlescence some or all of the light is white.
Artificial pigments and paints showing an iridescent effect are described as pearlescent, for example when used for car paints. Arthropods and molluscs: Chordates: The feathers of birds such as kingfishers, birds-of-paradise, parrots, grackles and peacocks are iridescent; the lateral line on the neon tetra is iridescent. A single iridescent species of gecko, Cnemaspis kolhapurensis, was identified in India in 2009; the tapetum lucidum, present in the eyes of many vertebrates, is iridescent. Plants: Many groups of plants have developed iridescence as an adaptation to use more light in dark environments such as the lower levels of tropical forests; the leaves of Southeast Asia's Begonia pavonina, or peacock begonia, appear iridescent azure to human observers due to each leaf's thinly layered photosynthetic structures called iridoplasts that absorb and bend light much like a film of oil over water. Iridescences based on multiple layers of cells are found in the lycophyte Selaginella and several species of ferns.
Meat: Minerals and compounds: Man-made objects: Nanocellulose is sometimes iridescent, as are thin films of gasoline and some other hydrocarbons and alcohols when floating on water. To create jewelry with crystal glass that lets light refract in a rainbow spectrum, Swarovski coats some of its products with special metallic chemical coatings and for example his Aurora Borealis gives the surface a rainbow appearance. A 2.2 MB GIF animation of a morpho butterfly showing iridescence "Article on butterfly iridescence"
The calliope hummingbird is a small hummingbird native to the United States and Canada and, during winter, Central America. It was considered the only member of the genus Stellula, but recent evidence suggests placement in the genus Selasphorus; this bird was named after the Greek muse Calliope. The former genus name means "little star"; this is the smallest breeding bird found in the United States. The only smaller species found in the U. S. is an accidental vagrant from Mexico. An adult calliope hummingbird can measure 7–10 cm in length, span 11 cm across the wings and weigh 2 to 3 g; these birds have glossy green on the crown with white underparts. Their bill and tail are short; the adult male has wine-red streaks on green flanks and a dark tail. Females and immatures have a pinkish wash on the flanks, dark streaks on the throat and a dark tail with white tips; the only similar birds are the rufous hummingbird and the Allen's hummingbird, but these birds are larger with more distinct and contrasting rufous markings on tail and flanks, longer central tail feathers.
The breeding habitat of calliope hummingbird is varied among open shrub altitudes. Nesting occurs at higher altitudes in the Rocky Mountains. Nests have been observed from as low as 300 m in Washington elevation to the tree line at over 3,000 m. In Montana, the minimum elevation observed. Open montane forest, mountain meadows, willow and alder thickets may variously serve as breeding grounds. During migration and winter, they occur in chaparral, lowland brushy areas and semi-desert regions, they nest in western North America from southern British Columbia and Alberta south to Colorado and southern California. During spring and summer, they move through Arizona and New Mexico and northern Mexico, to winter in southwestern Mexico as well as in Guatemala and Belize. Calliope hummingbirds are a migratory bird leaving their breeding grounds earlier than most birds to take advantage of the late-summer wildflowers in the mountains of western North America, they are believed to be the smallest-bodied long distance migrant in the world.
These birds feed on nectar from flowers using a long extendable tongue, drink sap from holes created by sapsuckers or catch insects on the wing. While collecting nectar, they assist in plant pollination. Plants preferred for pollinating include paintbrush, columbine, trumpet gilia, elephant head, they will occasionally catch and eat small insects and spiders. Adult males arrive on the breeding ground before females, from mid-April to early May; the male vigorously defends a nesting territory in which he will breed with many females. The male takes no part in raising the young and actually vacates the breeding grounds by the time the young hatch; the female builds an open cup nest in a conifer tree under an overhanging branch, though apple and alder trees have been used. The nest is built on the base of large pine cones and somewhat resembles a pine cone itself. A nest may be used over the course of several years. Two eggs are incubated for 15 to 16 days; the young are capable of flight about 20 days after hatching.
During courtship, a male calliope hummingbird hovers at accelerated wingbeat frequency up to 95 flaps per second, creating a loud buzzing sound, with throat feathers protruding and facing a female. The male ascends temporarily to 20 meters and dives at high speed, with the rapid descent causing sonation of wing and tail feathers combined with vocalization, intending to attract attention of the female. Research in a wind tunnel demonstrated that the male courtship display includes sounds produced by three independent feather or vocal components, each with different acoustic characteristics, thus containing different messages appealing to the female. Many species of pollinators, including the calliope hummingbird, have shown decreases in certain populations. Little information is available on the overall issues that are causing these declines but possible threats include habitat loss, increased use of pesticides, replacement of native plants by non-native plants; the restricted wintering range of calliope hummingbirds makes the species more susceptible to natural disasters, diseases, or land use changes that could wipe out significant portions of the population.
The calliope hummingbird has not been well studied. Calliope Hummingbird – Stellula calliope USGS Patuxent Bird Identification InfoCenter Calliope Hummingbird Species Account – Cornell Lab of Ornithology Calliope Hummingbird videos at the Internet Bird Collection Stamps
The rufous-breasted sabrewing is a species of hummingbird in the family Trochilidae. It is found in Brazil and Venezuela, its natural habitat is subtropical or tropical moist montane forest
The rufous sabrewing is a species of hummingbird in the family Trochilidae. It is found in El Salvador and Mexico, its natural habitats are subtropical or tropical moist montane forest and degraded former forest. Image at ADW
The violetears are hummingbirds of the genus Colibri. They are medium to large species found in Mexico, Central and northern South America; the Mexican violetear wanders as far north as the United States and Canada. Violetears have short or medium black bills. Three of the four species have a green plumage; the males have a violet blue patch running back and down from the eye, erected when they are excited, a glittering throat patch. The female plumage is like the male’s, but the ear and throat patches are smaller. Violetears build substantial cup nests into, they have loud persistent songs repetitions of double notes. These birds come to artificial nectar feeders, show no fear of humans, they are aggressively territorial, at feeders or flowering shrubs they spend much time chasing other hummingbirds, rather than feeding. Hilty, Birds of Venezuela, ISBN 0-7136-6418-5 Stiles and Skutch, A guide to the birds of Costa Rica ISBN 0-8014-9600-4 Birds of the World, 1999 Edition ISBN 0-7136-8989-9
Venezuela the Bolivarian Republic of Venezuela, is a country on the northern coast of South America, consisting of a continental landmass and a large number of small islands and islets in the Caribbean Sea. The capital and largest urban agglomeration is the city of Caracas, it has a territorial extension of 916,445 km2. The continental territory is bordered on the north by the Caribbean Sea and the Atlantic Ocean, on the west by Colombia, Brazil on the south and Tobago to the north-east and on the east by Guyana. With this last country, the Venezuelan government maintains a claim for Guayana Esequiba over an area of 159,542 km2. For its maritime areas, it exercises sovereignty over 71,295 km2 of territorial waters, 22,224 km2 in its contiguous zone, 471,507 km2 of the Caribbean Sea and the Atlantic Ocean under the concept of exclusive economic zone, 99,889 km2 of continental shelf; this marine area borders those of 13 states. The country has high biodiversity and is ranked seventh in the world's list of nations with the most number of species.
There are habitats ranging from the Andes Mountains in the west to the Amazon basin rain-forest in the south via extensive llanos plains, the Caribbean coast and the Orinoco River Delta in the east. The territory now known as Venezuela was colonized by Spain in 1522 amid resistance from indigenous peoples. In 1811, it became one of the first Spanish-American territories to declare independence, not securely established until 1821, when Venezuela was a department of the federal republic of Gran Colombia, it gained full independence as a country in 1830. During the 19th century, Venezuela suffered political turmoil and autocracy, remaining dominated by regional caudillos until the mid-20th century. Since 1958, the country has had a series of democratic governments. Economic shocks in the 1980s and 1990s led to several political crises, including the deadly Caracazo riots of 1989, two attempted coups in 1992, the impeachment of President Carlos Andrés Pérez for embezzlement of public funds in 1993.
A collapse in confidence in the existing parties saw the 1998 election of former coup-involved career officer Hugo Chávez and the launch of the Bolivarian Revolution. The revolution began with a 1999 Constituent Assembly, where a new Constitution of Venezuela was written; this new constitution changed the name of the country to Bolivarian Republic of Venezuela. The sovereign state is a federal presidential republic consisting of 23 states, the Capital District, federal dependencies. Venezuela claims all Guyanese territory west of the Essequibo River, a 159,500-square-kilometre tract dubbed Guayana Esequiba or the Zona en Reclamación. Venezuela is among the most urbanized countries in Latin America. Oil was discovered in the early 20th century, today, Venezuela has the world's largest known oil reserves and has been one of the world's leading exporters of oil; the country was an underdeveloped exporter of agricultural commodities such as coffee and cocoa, but oil came to dominate exports and government revenues.
The 1980s oil glut led to a long-running economic crisis. Inflation peaked at 100% in 1996 and poverty rates rose to 66% in 1995 as per capita GDP fell to the same level as 1963, down a third from its 1978 peak; the recovery of oil prices in the early 2000s gave. The Venezuelan government under Hugo Chávez established populist social welfare policies that boosted the Venezuelan economy and increased social spending, temporarily reducing economic inequality and poverty in the early years of the regime. However, such populist policies became inadequate, causing the nation's collapse as their excesses—including a uniquely extreme fossil fuel subsidy—are blamed for destabilizing the nation's economy; the destabilized economy led to a crisis in Bolivarian Venezuela, resulting in hyperinflation, an economic depression, shortages of basic goods and drastic increases in unemployment, disease, child mortality and crime. These factors have precipitated the Venezuelan Migrant Crisis where more than three million people have fled the country.
By 2017, Venezuela was declared to be in default regarding debt payments by credit rating agencies. In 2018, the country's economic policies led to extreme hyperinflation, with estimates expecting an inflation rate of 1,370,000% by the end of the year. Venezuela is a charter member of the UN, OAS, UNASUR, ALBA, Mercosur, LAIA and OEI. According to the most popular and accepted version, in 1499, an expedition led by Alonso de Ojeda visited the Venezuelan coast; the stilt houses in the area of Lake Maracaibo reminded the Italian navigator, Amerigo Vespucci, of the city of Venice, Italy, so he named the region Veneziola, or "Little Venice". The Spanish version of Veneziola is Venezuela. Martín Fernández de Enciso, a member of the Vespucci and Ojeda crew, gave a different account. In his work Summa de geografía, he states that the crew found indigenous people who called themselves the Veneciuela. Thus, the name "Venezuela" may have evolved from the native word; the official name was Estado de Venezuela, República de Venezuela, Estados Unidos de Venezuela, a
Colombia the Republic of Colombia, is a sovereign state situated in the northwest of South America, with territories in Central America. Colombia shares a border to the northwest with Panama, to the east with Venezuela and Brazil and to the south with Ecuador and Peru, it shares its maritime limits with Costa Rica, Honduras, Jamaica and the Dominican Republic. Colombia is a unitary, constitutional republic comprising thirty-two departments, with the capital in Bogota. Colombia has been inhabited by various indigenous peoples since 12,000 BCE, including the Muisca and the Tairona, along with the Inca Empire that expanded to the southwest of the country; the Spanish arrived in 1499 and by the mid-16th century conquered and colonized much of the region, establishing the New Kingdom of Granada, with Santafé de Bogotá as its capital. Independence from Spain was achieved in 1819, but by 1830 the "Gran Colombia" Federation was dissolved, with what is now Colombia and Panama emerging as the Republic of New Granada.
The new nation experimented with federalism as the Granadine Confederation, the United States of Colombia, before the Republic of Colombia was declared in 1886. Panama seceded in 1903. Beginning in the 1960s, the country suffered from an asymmetric low-intensity armed conflict and rampant political violence, both of which escalated in the 1990s. Since 2005, there has been significant improvement in security and rule of law. Colombia is one of the most ethnically and linguistically diverse countries in the world, with its rich cultural heritage reflecting influences by indigenous peoples, European settlement, forced African migration, immigration from Europe and the Middle East. Urban centres are located in the highlands of the Andes mountains and the Caribbean coast. Colombia is among the world's 17 megadiverse countries, the most densely biodiverse per square kilometer. Colombia is a middle power and regional actor in Latin America, it is part of the CIVETS group of six leading emerging markets and a member of the UN, the WTO, the OAS, the Pacific Alliance, other international organizations.
Colombia's diversified economy is the fourth largest in Latin America, with macroeconomic stability and favorable long-term growth prospects. The name "Colombia" is derived from the last name of Christopher Columbus, it was conceived by the Venezuelan revolutionary Francisco de Miranda as a reference to all the New World, but to those portions under Spanish rule. The name was adopted by the Republic of Colombia of 1819, formed from the territories of the old Viceroyalty of New Granada; when Venezuela and Cundinamarca came to exist as independent states, the former Department of Cundinamarca adopted the name "Republic of New Granada". New Granada changed its name in 1858 to the Granadine Confederation. In 1863 the name was again changed, this time to United States of Colombia, before adopting its present name – the Republic of Colombia – in 1886. To refer to this country, the Colombian government uses the terms Colombia and República de Colombia. Owing to its location, the present territory of Colombia was a corridor of early human migration from Mesoamerica and the Caribbean to the Andes and Amazon basin.
The oldest archaeological finds are from the Pubenza and El Totumo sites in the Magdalena Valley 100 kilometres southwest of Bogotá. These sites date from the Paleoindian period. At Puerto Hormiga and other sites, traces from the Archaic Period have been found. Vestiges indicate that there was early occupation in the regions of El Abra and Tequendama in Cundinamarca; the oldest pottery discovered in the Americas, found at San Jacinto, dates to 5000–4000 BCE. Indigenous people inhabited the territory, now Colombia by 12,500 BCE. Nomadic hunter-gatherer tribes at the El Abra, Tibitó and Tequendama sites near present-day Bogotá traded with one another and with other cultures from the Magdalena River Valley. Between 5000 and 1000 BCE, hunter-gatherer tribes transitioned to agrarian societies. Beginning in the 1st millennium BCE, groups of Amerindians including the Muisca, Zenú, Tairona developed the political system of cacicazgos with a pyramidal structure of power headed by caciques; the Muisca inhabited the area of what is now the Departments of Boyacá and Cundinamarca high plateau where they formed the Muisca Confederation.
They farmed maize, potato and cotton, traded gold, blankets, ceramic handicrafts and rock salt with neighboring nations. The Tairona inhabited northern Colombia in the isolated mountain range of Sierra Nevada de Santa Marta; the Quimbaya inhabited regions of the Cauca River Valley between the Western and Central Ranges of the Colombian Andes. Most of the Amerindians practiced agriculture and the social structure of each indigenous community was different; some groups of indigenous people such as the Caribs lived in a state of permanent war, but others had less bellicose attitudes. The Incas expanded their empire onto the southwest part of the country. Alonso de Ojeda reached the Guajira Peninsula in 1499. Spanish explorers, led by Rodrigo de Bastidas, made the first exploration