The Golden Age of Greece, also referred to as the Classical Period, took place in Greece in the 5th and 4th Centuries BC. This era started when the age of tyranny in Athens finished. Peisistratus, a  known tyrant, died in 528 BC. It took until 510 BC for Greek society to stabilize and begin to flourish once again. This was followed by the rule of Alexander the Great, which was a time of remarkable growth for the Greek people. The end of the Golden Age occurred when Alexander passed away in 323 BC. The Golden Age of Greece was one of the most important times in Greek history. It was a time of remarkable cultural growth, and this is what people most often think of when they picture this time period. Greek theater was invented during this time, and plays written by dramatists such as Aeschylus, Aristophanes, Euripides are still performed today. Other things, such as the Olympic Games were also popular during this time period. This is also when democracy was invented and the Athenian Parthenon was built. This is when the noted philosophers, Socrates and Aristotle, were alive. Socrates' method of questioning is still modeled today in today’s schools and universities. Aristotle was one of Socrates’ students who made important contributions to philosophy and intellectual thought. He was also one of Alexander the Great’s tutors when Alexander was a child.

The Enlightenment was an intellectual and philosophical movement that dominated the world of ideas in Europe during the 17th to 19th centuries. The Enlightenment emerged out of a European intellectual and scholarly movement known as Renaissance humanism and was also preceded by the Scientific Revolution and the work of Francis Bacon. French historians traditionally date the Enlightenment from 1715 to 1789, from the death of Louis XIV of France until the outbreak of the French Revolution that ended the Ancient Regime. Philosophers and scientists of the period widely circulated their ideas through meetings at scientific academies, Masonic lodges, literary salons, coffeehouses, and in printed books, journals, and pamphlets. The ideas of the Enlightenment undermined the authority of the monarchy and the Catholic Church and paved the way for the political revolutions of the 18th and 19th centuries. A variety of 19th-century movements, including liberalism and neoclassicism, trace their intellectual heritage to the Enlightenment. The Enlightenment included a range of ideas centered on the sovereignty of reason and the evidence of the senses as the primary sources of knowledge and advanced ideals such as liberty, progress, toleration, fraternity, constitutional government, and separation of church and state.

Whereas planetary orbits tend to be nearly circular, those of comets are elliptical`like stretched-out rubber bands.  The reappearance of a comet is proportional to the length of its orbit.  Halley's comet completes its trek approximately once every 75 years, whereas the lesser magnitude Enke comet makes its rounds in a mere 3.3 years.  Other comets, such as Hyakutake (1996), have such elongated orbits that they may pass through the solar system only once every thousand years or more.|There are three constituent parts of a comet: the nucleus, the coma, and the tail.  The nucleus of a comet is composed of primarily silicate dust particles embedded in ice; hence, the comet has been informally dubbed a "dirty snowball."  Surrounding the nucleus is a vaporous coma of dust and gases that extends for tens of thousands of miles.|When a comet approaches the sun, its tail develops rapidly.  Blasted by solar winds and light pressure, gases and dust are forced away from the coma, forming a forked tail.  A comet's tail always points away from the sun, somewhat analogous to long hair being blown back by a wind.  The tail increases in length as the comet approaches perihelion, its closest distance to the sun.  In the 1910 appearance of Halley's comet, the tail was calculated to be some 150 million miles in length.  As a comet retreats from the sun, its resplendent tail and glowing coma begin to wane, disappearing completely as the comet nears aphelion, the farthest point away from the sun in its long, elliptical journey.

From ancient times, amber has had a strong allure, with its warm color, resinous feel, translucence, and curious flecks trapped beneath its surface.  As early as the Neolithic period, people were carving amber into figures and symbols which were worn as special charms or used for adornment.  Today, however, amber has attracted a new audience, scientists who are interested in studying the unusual flecks.  These tiny spots in amber are of interest to scientists because many are actually preserved organisms inside the amber.|Though often used in jewelry, amber is not a precious stone, a semi-precious stone, or even a mineral.  Instead, it is the fossilized resin, or gum, from trees.  It differs from other fossils, however, in that other fossils are generally mineral replacements of original structures, while amber is entirely organic; i.e., it is derived from living organisms.  In the millions of years that it takes for amber to form, its composition has stayed substantially the same as that of the resin that formed it.|Large deposits of amber in the Dominican Republic and Mexico are 25 to 30 million years old, and the eastern Baltic region boasts huge deposits of amber that are 15 million years older.  The extreme age of amber, coupled with its organic make-up, have caused amber to become the focus of recent scientific interest.  Modern technology has been used to determine that the tiny organisms caught in amber have been preserved to a remarkable degree due to the organic nature of the amber; soft tissue, cellular detail, and DNA of ancient organisms have all been preserved, providing information that cannot be obtained from other fossils of that age.

Snow is the precipitation of ice in the form of flakes, clusters, or crystals.  Snow crystals are formed in the atmosphere at freezing temperatures when water vapor is condensed to ice without passing through a liquid state.  These snow crystals often fall to the ground as individual units, but in warmer regions they clump together as they fall, creating snowflakes.  Almost 50 percent of rain was once snow that melted as it entered warmer temperatures on its way to earth. |The study of snow crystals has been going on for more than four centuries.  Many people have been intrigued by snow, and in the process of observing its forms and studying its formation, they have created a collection of its images. The first sketch was made in 1550 by Olaus Magnus, archbishop of Uppsala, and in 1635, the first scientific records were made by French philosopher, Rene Descartes.  Two centuries later, English meteorologist James Glaisher produced a drawing that is considered the most accurate image made before the development of photomicrography.  The pioneer in this advanced technology was Wilson Alwyn Bentley, a farmer in Jericho, Vermont.  He began his work in 1885, spending all of his free time outside in the cold taking pictures of snowflakes.  By the time of his death 40 years later, he had made 6,000 photos, half of which were later published. |From these studies and the resulting data, science has learned much about the snowflake.  Snowflakes are transparent, like glass, and vary in size from .02 inches to .50 inches in diameter.  Although an infinite number of snowflakes fall every year, no two have been found that are alike.  However, all natural snowflakes are six-sided and consist of flat-plated ice crystals.  These hexagonal clumps of ice create a winter wonderland in nearly every part of the world each year.

Every day, millions of shoppers search for the perfect gifts. They buy them for holidays, weddings, birthdays, anniversaries and myriad of other celebrations. Many people relish the opportunity to buy presents because they believe it offers a powerful means to build stronger bonds with their peers. However, many worry that their purchase will disappoint the recipients. Anthropologists believe gift-giving is a positive social. On the other hand, economists describe it as a waste of resources. According to them, people buy presents that recipients would not choose to buy or spend less money to purchase. This is not surprising to social psychologists either. Research has found that people struggle to take account of others’ perspectives. They equate how much they spend with how much with how much recipients will appreciate the gift. However this assumption may be unfounded. According to scientists, gift-givers signal their positive attitude and willingness to invest in their future through gift giving. Ergo, gift-givers believe that with expensive gifts they are sending stronger feelings.

The seemingly simple question of “what defines a sport?” has been the fodder for argument and conversation for years, among professional and armchair athletes alike. There seems to be no doubt that vigorous and highly competitive activities such as baseball, football, and soccer are truly “sports,” but when the subject of other activities such as darts, chess, and shuffleboard is broached we find ourselves at the heart of a controversy. 

If say, billiards, is not a sport, then what exactly is it? Those who would dispute it to be a sport would respond that it is a simple leisure activity. They would go on to claim a true sport first and foremost requires some form of physical exertion. More to the point, if a player does not break a sweat, what he or she plays is not a sport. Beyond that, more important criteria would be the need for decent hand-eye coordination, and the ever-present possibility of sustaining injury. Billiards only fits one of those specifications (hand-eye coordination), so according to the doubters, it is not a real sport. 

To help resolve this dispute, the first text to consult would have to be the dictionary. According to one dictionary, a sport is defined as “a diversion” or a “recreation.” Assuming one strictly adheres to the simple guidelines laid out in that definition, it would seem that almost any activity that provides enjoyment could be classified as a sport. And if, according to the dictionary, watching a sport on television is a sport itself, I guess that would make a couch potato an athlete. Play ball!

According to Kant, knowledge should not be seen as representing objects that exist independently of      our judgments. Such objects should not be construed as existing both out there in the world and in our minds behind sensory experience (as rationalists argue), nor as arising directly out of sensory experiences, which then get pieced together by ideas (as empiricists argue). For Kant, neither view concerns dimensions of consciousness, which are crucial for relating the conditions of human knowledge to ethical and moral issues. Human beings are not only able to attribute meaning and value to experience, but can discover that they themselves are the source of those meanings and values. Kant attributes this not only to reason but to imagination. Imagination, for Kant, makes it possible for human beings to discover that they are themselves sources of meanings and values, a discovery necessary for individual consciousness of freedom and for re-solving discrepancies between is and ought in society and history.

Planting a garden is a lot like having a family. Both require a great deal of work, especially as they grow and as the seasons change. As summer days lengthen, your plants become dependent on you for sustenance, much like your children depend on you for food and drink. Like a thirsty child asking for a drink of water, your plants do the same. Their bent, wilted “body” language, translated, issues a demand much the way your child requests milk or juice. When their collective thirsts are quenched, you seethe way they both thrive in your care. The fussy child becomes satisfied, and the plant reaches toward the sun in a showy display. You might also fi nd that you have to clean the space around your plants much like you would pick up toys and clothes that have been thrown helter-skelter in your toddler’s room. Similarly, plants shed spent petals, roses need to be pruned, and weeds need to be pulled. To keep children healthy, parents protect their children against disease with medicine, and gardeners do the same with insect repellent. To nourish them, parents give children vitamins, and gardeners use fertilizer, as both promote healthy growth. As children grow and become adults, they need less and less care. However, here’s where the similarity ends. While plants die and become dormant during winter, children still maintain a vital role in the family unit.

The modern Olympic Games or Olympics are leading international sporting events featuring summer and winter sports competitions in which thousands of athletes from around the world participate in a variety of competitions. The Olympic Games are considered the world's most important sports competition with more than 200 nations participating. They are normally held every four years. The Olympic motto is "Citius, Altius, Fortius", which is Latin for "Faster, Higher, Stronger". The "Olympic rings" are five interlocking rings, colored blue, yellow, black, green, and red on a white field. The symbol was originally created in 1913 by Coubertin. He appears to have intended the rings to represent the five continents: Europe, Asia, Africa, America, and Oceania. The creation of the Olympic games was inspired by the ancient Olympic Games, which were held in Olympia, Greece, from the 8th century BC to the 4th century AD. In the Summer Olympic Games and Winter Olympic Games, Olympic sports are contested. There are also the Paralympic Games for athletes with a disability, the Youth Olympic Games for athletes aged 14 to 18, the five Continental games (Pan American, African, Asian, European, and Pacific), and the World Games for sports that are not contested in the Olympic Games.

The arabesque is a form of artistic decoration consisting of surface decorations or plain lines, often combined with other elements. Within the very wide range of Eurasian decorative art that includes motives matching this basic definition, the term "arabesque" is used consistently as a technical term by art historians to describe only elements of the decoration found in two phases: Islamic art from about the 9th century and onward, and European decorative art from the Renaissance and onward. Interlace and scroll decoration are terms used for most other types of similar patterns. Arabesques are a fundamental element of Islamic art. Arabesque designs on surfaces create a sense of pleasing overall rhythm and patterns. As the Islamic religion spread, arabesques could be found on walls of mosques and palaces, on ceramic tiles and vessels, and on glassware. Some Western arabesques derive from Islamic art, but others are closely based on ancient Roman decorations. In the West, arabesques are essentially found in the decorative arts. Because of the generally non-figurative nature of Islamic art, arabesque decoration is often a very important element and plays a large part in the decoration of architecture.

Opal is a noncrystalline mineral that has been used as a gemstone in numerous cultures for thousands of years.  Quantities of high-grade opal have been mined in diverse areas worldwide, including eastern Europe, Australia, and Mexico, as well as in the states of California, Nevada, and Idaho in the United States.|Some varieties of opal contain flashes of a wide spectrum of colors, while others do not.  Those types of opal with tiny specks of iridescent color are called precious opal.  Varieties without this iridescent coloration throughout are called common opal.  It is the precious opal, with its rainbow-like assortment of colors dotting the stone that has been considered gemstone quality over the ages.  Precious opal has numerous colors that serve as a background for the iridescent specks, the most valuable of which are black, white, and blue opal, as well as the reddish-brown stone known as fire opal.|In some cultures, precious opal is recognized not only as a gemstone of great attraction but also as an omen of bad luck.  Much of the superstition surrounding opal is now believed to have arisen from the tendency of opal to dry out and crack.  Opal is a hydrated mineral with a water content that ranges from 1 percent to 21 percent.  The hardness of a particular opal depends upon its water content, which can vary and can be particularly low in dry climates.  Throughout its long history, the negative superstition surrounding opal has been related to the tendency of opal to crack seemingly spontaneously, without any noticeable justification.  A crack in an opal has been viewed as an indication that bad luck is on its way.  In reality, though, a seemingly spontaneous crack in a stone is most likely due to a loss of essential water.

A number of staple crops are today quite commonplace in much of the world and feed much of today's population.  These staple crops of today originated in different eras and in different parts of the world before spreading throughout the rest of the globe.

Wheat was probably the earliest cereal to have been grown and most likely was a hybrid of wild grasses rather than a single wild grass.  It is known to have been cultivated by Mediterranean civilizations 10,000 years ago and was being used as a primary ingredient in baked goods in Mesopotamia as early as 8000 B.C.

Beans are a diverse family of plants that have been cultivated for 8,000 years.  Certain types of beans, such as mung and soy, were first cultivated in Asia, while other types of beans, such as string and lima, are thought to have originated in the Americas.

Other crops that originated in the Americas are potatoes and maize, a relative of corn; maize was used extensively beginning around 5000 B.C. in civilizations in what is today Mexico, while the cultivation of the potato developed in civilizations in the Andes at least as early as 100 B.C.  Maize and potatoes were staples of the diets of their respective cultures long before they were introduced to Europe in the sixteenth century by European explorers who had discovered them in the Americas.

The cultivation of rice is not as old as the cultivation of wheat, beans, and maize.  Rice was first known to have been cultivated in India around 3000 B.C.  From there, it later spread to China, Japan, and various countries in Southeast Asia, which are today major producers of the crop.

The apple, a juicy fruit that grows from pink or white flowers, is cultivated widely in orchards across North America.  At least two varieties of apples are cultivated together in one orchard due to the fact that the flowers of one type of apple tree must be pollinated by a different variety of apple.  The point in the springtime when the apple blossoms appear is the most critical time for apples: there have to be enough bees to pollinate each flower and warm enough weather to facilitate their work.  Apple growers watch the temperatures anxiously at this time of year because frozen flowers or fruit spells disaster for the crop.  Workers may have to get up at any hour of the night to blow away the cold air with fans, heat the orchard air with fire pots, or wet the trees down to keep the frost away.

The first step in getting apples from orchard to market is to pick them.  The picking must be done carefully to ensure that the spur, which produces the fruit, is not damaged.  Apples used to be collected in bushel baskets and taken to market, but today bins of apples are trucked to packing houses, where they go through many sortings before they get to the grocery store display.  As a first step, the smallest apples, called "chops," are eliminated to make juice.  Apples with many flaws, or imperfections, are called "processors"; they are used for pie slices or are made into sauce because of their less-than-perfect appearance.  The "fancy" grade apples are stored in a controlled atmosphere; adjusting the oxygen content from 20 percent to 2 percent and keeping the temperature between 31 and 32 degrees Fahrenheit keeps the apples alive but prevents overripening.  The humidity is kept around 95 percent so that the apples remain crisp and fresh.  Before shipping, the apples are washed, rinsed, dried, and coated with a thin film of hot wax for beautification.

Once the apples have cleared the marketplace, they are put to various uses.  Apples are 87 percent water, making them great for juicing.  The fresh juice that is made from apples is called cider, and this cider can be fermented into applejack.  Apples are not only used to make beverages; they can also be used to make products such as apple butter, vinegar, applesauce, and one of America's favorite desserts, apple pie.

An octopus is a sea creature quite capable of inspiring fear in an unsuspecting swimmer or diver unlucky enough to paddle across one unexpectedly.  There is a basis for a healthy fear of an octopus.  An octopus is quite strong, in large part due to the suckers on its arms.  A common octopus has 240 suckers per arm for a whopping total of 1,920 suckers on all of its arms.  Were an octopus to hold onto an object (or a person, for that matter) with all eight of its arms, a quarter of a ton of force would be needed to loosen its grip.  Another reason wariness for an octopus is not unwarranted is that some types of octopuses are poisonous.  A bite from a venomous type of octopus will undoubtedly cause a stinging pain and may, if left unattended, lead to death within a few hours.

While maintaining a healthy distance from an octopus may be a reasonable position, it is also quite arguable that an octopus poses little threat to humans.  An octopus is shy and timid by nature, much more comfortable hiding out in undersea nooks and crannies or burrowing into the sandy bottom than in seeking out conflict.  An octopus only strikes out when it feels threatened, when an unexpected invader enters its undersea lair or a potential attacker gets too close.  In this situation, an octopus may attack by biting or wrapping its arms around the threatening force.

An octopus, in reality, is much more concerned with avoidance than attack and has a couple of specialized methods of getting away from potential attackers.  One method is to eject forceful jets of water.  These high-powered streams of water allow an octopus to make a high-speed exit from a dangerous location.  Another technique that the octopus uses when eluding a danger is to eject a volume of dark-colored ink.  The ink temporarily clouds the water and confuses the sense of smell of the attacker while the octopus quickly flees.

There are many legends about how William Shakespeare got his start in the theater.  One states that he began by holding gentlemen's horses at the playhouse door.  Others say that he was a servant, a prompter's assistant, or a call boy.  In the period between 1592 and 1594, theatrical companies were somewhat disorganized; Shakespeare apparently decided to take advantage of this situation and, casting off the garb of a servant, presented himself as a poet.  His two narrative poems, (Venus and Adonis and The Rape of Lucrece, were published during this period, in 1593 and 1594 respectively. 

In 1594, Shakespeare made the change from player and poet to actor and playwright.  There were two principal theatrical companies at this point in the Elizabethan Age, the Lord Chamberlain's Men and the Lord Admiral's Men.  By 1595, Shakespeare was a leading member of one of the two, the Lord Chamberlain's Men, and a sharer in that company.  It was a position of both promise and profit inasmuch as the company was soon to become the King's Men with the accession to the throne of King James I.

Known today as one of the greatest playwrights of the English language, Shakespeare was a vital part of the King's Men and played a major role in its success and popularity.  In the beginning, his primary role with the company was as a superb actor and great draw.  However, after 1603 his name as the principal actor no longer appeared in the credits; from that time on his chief contribution to the company, and to the world, was his plays.  His work was the most substantial of the King's Men repertoire during that period and continues to this day to bring the public out to the playhouse.

During a relatively short period at the end of the nineteenth century, George Eastman was instrumental in transforming the labor-intensive and expensive art of photography into a popular and affordable hobby.  The phenomenal success that Eastman had in these early years of his business was in most part due to the successful innovation that opened up photography to the population as a whole.|While Eastman was working as a bookkeeper in a bank in Rochester, New York, he spent his leisure time working on a process for making dry plates.  By 1880, Eastman had perfected the process.  Without leaving his job at the bank, he established the Eastman Dry Plate Company.  The business grew so quickly that by 1881 Eastman had given up his job at the bank in order to develop the business.|Changes to simplify the process of taking photographs followed one after another.  In 1884, Eastman took a step that made photography a less cumbersome process: he replaced the unwieldy glass plates with paper-backed roll film.  Four years later, the hand-held Kodak was introduced.  This camera came loaded with enough film to take a hundred photographs and produced round-shaped pictures approximately six centimeters in diameter.  Something that made this camera very popular was that a photographer did not need to know how to develop film in order to use it; after using up the film, the photographer sent the loaded camera back to the factory, where the photographs were processed and the camera was reloaded and returned to its owner.  In 1892, another innovation, film that could be loaded in the daylight, allowed amateur photographers to load their own film successfully.

The mechanism for evolution was conceived by Charles Darwin in the mid-nineteenth century. He spent time exploring the natural world on different expeditions. From 1831 to 1836, Darwin traveled around the world. His journey included stops at several island chains. On these islands, Darwin observed species of organisms that were clearly similar, but they had distinct differences. Darwin thought that the island species might be all modified from one original mainland species. Darwin conceived a mechanism to explain how and why such changes could take place. He called this mechanism natural selection. Natural selection was an outcome of three principles that happened in nature. First, the characteristics of organisms are inherited. Second, more offspring are produced than are able to survive. Therefore, there is a competition for limited  resources in each generation. Third, offspring vary among each other in regard to their characteristics and those variations are inherited. Out of these three principles, Darwin reasoned that offspring with inherited characteristics that allow them to best compete for limited resources will survive and have more offspring than those individuals with variations that are less able to compete. Because characteristics are inherited, these traits will be better represented in the next generation. This will lead to change in populations over generations.

The walnut tree produces wood that is used for countless purposes, and is considered the finest wood in the world. The wood is easy to work with, yet it is very hard and durable—and when it is polished, it produces a rich, dark luster. It also shrinks and swells less than any other wood, which makes it especially desirable for fine furniture, flooring, and even gun stocks. In fact, just about every part of the walnut is unusually hard and strong. The nut of the tree is encased inside a very hard shell, which itself is enclosed in a leathery outer covering called a husk. It requires real effort to break through those layers to get at the tasty meat inside. Yet every part of the walnut is useful to people. The outer husk produces a dark reddish stain that is hard to remove from the hands of the person who opens the nut, and this pigment is widely used in dyes and wood stains. The inner shell is used as an abrasive to clean jet engines. And the meat of the nut is extensively used in cooking, ice cream, flavorings—and just eaten raw. Walnut trees exude a chemical into the soil near their roots which can be poisonous to some trees and shrubs. Fruit trees, for example, will not survive if planted too close to a walnut. Many other plants, such as maple trees or ivy, are not affected by the walnut’s presence, and are well-suited to grow in its vicinity.

The modem comic strip started out as ammunition in a newspaper war between giants of the American press in the late nineteenth century. The first full-color comic strip appeared in January 1894 in the New York World, owned by Joseph Pulitzer. The first regular weekly full-color comic supplement, similar to today's Sunday funnies, appeared two years later, in William Randolph Hearst's rival New York paper, the Morning Journal. Both were immensely popular, and publishers realized that supplementing the news with comic relief boosted the sale of papers. The Morning Journal started another feature in 1896, the "Yellow Kid," the first continuous comic character in the United States, whose creator, Richard Outcault, had been lured away from the World by the ambitious Hearst. The "Yellow Kid" was in many ways a pioneer. Its comic dialogue was the strictly urban farce that came to characterize later strips, and it introduced the speech balloon inside the strip, usually placed above the characters' heads. The first strip to incorporate all the elements of later comics was Rudolph Dirks's "Katzenjammer Kids," based on Wilhelm Busch's Max and Moritz, a European satire of the nineteenth century. The "Kids" strip, first published in 1897, served as the prototype for future American strips. It contained not only speech balloons, but a continuous cast of characters, and was divided into small regular panels that did away with the larger panoramic scenes of most earlier comics. Newspaper syndication played a major role in spreading the popularity of comic strips throughout the country. Though weekly colored comics came first, daily black and-white strips were not far behind. They first appeared in the Chicago American in1904. It was followed by many imitators, and by 1915 black-and-white comic strips had become a staple of daily newspapers around the country.

Every drop of water in the ocean, even in the deepest parts, responds to the forces that create the tides. No other force that affects the sea is so strong. Compared with the tides, the waves created by the wind are surface movements felt no more than a hundred fathoms below the surface. The currents also seldom involve more than the upper several hundred fathoms despite their impressive sweep. The tides are a response of the waters of the ocean to the pull of the Moon and the more distant Sun. In theory, there is a gravitational attraction between the water and even the outermost star of the universe. In reality, however, the pull of remote stars is so slight as to be obliterated by the control of the Moon and, to a lesser extent, the Sun. Just as the Moon rises later each day by fifty minutes, on the average, so, in most places, the time of high tide is correspondingly later each day. And as the Moon waxes and wanes in its monthly cycle, so the height of the tide varies. The tidal movements are strongest when the Moon is a sliver in the sky, and when it is full. These are the highest flood tides and the lowest ebb tides of the lunar month and are called the springtides. At these times the Sun, Moon, and Earth are nearly in line and the pull of the two heavenly bodies is added together to bring the water high on the beaches, to send its surf upward against the sea cliffs, and to draw a high tide into the harbors. Twice each month, at the quarters of the Moon, when the Sun, Moon and Earth lie at the apexes of a triangular configuration and the pull of the Sun and Moon are opposed, the moderate tidal movements called neap tides occur. Then the difference between high and low water is less than at any other time during the month.

Birds that feed in flocks commonly retire together into roosts. The reasons for roosting communally are not always obvious, but there are some likely benefits. In winter especially, it is important for birds to keep warm at night and conserve precious food reserves. One way to do this is to find a sheltered roost. Solitary roosters shelter in dense vegetation or enter a cavity – horned larks dig holes in the ground and ptarmigan burrow into snow banks – but the effect of sheltering is magnified by several birds huddling together in the roosts, as wrens, swifts, brown creepers, bluebirds, and anis do. Body contact reduces the surface area exposed to the cold air, so the birds keep each other warm. Two kinglets huddling together were found to reduce their heat losses by a quarter, and three together saved a third of their heat. The second possible benefit of communal roosts is that they act as "information centers." During the day, parties of birds will have spread out to forage over a very large area. When they return in the evening some will have fed well, but others may have found little to eat. Some investigators have observed that when the birds set out again next morning, those birds that did not feed well on the previous day appear to follow those that did. The behavior of common and lesser kestrels may illustrate different feeding behaviors of similar birds with different roosting habits. The common kestrel hunts vertebrate animals in a small, familiar hunting ground, whereas the very similar lesser kestrel feeds on insects over a large area. The common kestrel roosts and hunts alone, but the lesser kestrel roosts and hunts in flocks, possibly so one bird can learn from others where to find insect swarms. Finally, there is safety in numbers at communal roosts since there will always be a few birds awake at any given moment to give the alarm. But this increased protection is partially counteracted by the fact that mass roosts attract predators and are especially vulnerable if they are on the ground. Even those in trees can be attacked by birds of prey. The birds on the edge are at greatest risk since predators find it easier to catch small birds perching at the margins of the roost.