小鸟用英文介绍

ntroductionBirds are warm bodied creatures with wings and feathers. The body temperature of birds is generally higher than that of humans, so they seem warm to the touch. Birds lay eggs which they incubate until hatching -- or, in some cases, get some other bird to do the incubating. In some species such as our songbirds, the young hatch naked and helpless and must be fed and cared for by a parent bird. Others, like the chickens and their relatives, produce down-covered young that are able run about and feed themselves. They are still dependent for protection upon adult birds.Birds range in size from thumb-sized hummingbirds to ostriches larger than a big man. Most birds, of course, fall somewhere between these two extremes. One common bird, the American Robin is about 10 inches in length, approximately the handspan of a large man. The smallest american birds are some species of hummingbird that could nest and raise a family in the cupped palm of a child. The largest are the cranes and herons, which, when standing erect, are almost eye-to-eye with a human adult. The nearly extinct California Condor has a wing span of almost 10 feet, and the Bald Eagle spans 7 feet.Birds walk, run, hop, swim, perch, cling, fly and even dig. They live in woodlands, open areas, cities, farms, lakes, swamps -- even the open ocean. They lay their eggs and raise their young in holes in the ground, in nests of varying complexity in vegetation or on the ground, in holes in trees, in human-constructed nest boxes, and in or on various parts of buildings. Go to IndexEvolutionary HistoryAccording to the best evidence paleontologists have found, birds evolved from dinosaurs or from a near relative of the dinosaurs during the Mesozoic Era. Early types of birds had teeth -- unlike modern birds which have toothless beaks -- and seemed intermediate between their reptilian ancestors and their modern descendents. Birds evolved feathers and light hollow bones which allow them to fly, though some species later returned to life on solid ground. Flying birds have powerful muscles anchored to special bones in the breast. Go to IndexMigrationMany birds are migratory, nesting and raising their young in temperate or higher latitudes during the warm months and spending the winter in tropical or sub-tropical areas. Some of these species make prodigious journeys of thousands of miles twice a year. The Arctic Tern nests in high lattitudes of the northern hemisphere and spends the rest of the year at the opposite end of the earth, the high lattitudes of the southern hemisphere. The thumb- sized Ruby-throated Hummingbird crosses the Caribbean non-stop twice each year. At the beginning of the journey, it rests and fills up on food to provide it energy for this tremendous feat. Go to IndexBird songsBird voices are often the key to their identification. Some species can hardly be told apart without hearing them call. The songs we hear in our gardens -- generally in the spring and summer -- are territorial and mating advertisements. The song, usually sung by a male, announces that he has staked out a particular piece of turf for his own and warns other males away. At the same time, the song announces to interested females the presence of a potential father for their young.The songs of birds vary from species to species, and skilled birders can identify the species in a particular area by sound alone. While some songs are often complex or variable and sometimes difficult to tell apart, most people can learn fairly quickly to identify a few of the most common near where they live. In fact, birdwatching is really as much bird listening as it is anything else. For this reason, many people who are completely blind or have low enough vision not to be able to see birds in the field can have be very successful in identifying the species around them.Not all birds sing, but they usually make other identifiable sounds. The familiar call of the various species of Chickadee in North America isn't actually a song, but rather a call indicating excitement or alarm. The actual song of Chickadees is much more obscure. Birds make a variety of sounds ranging from territorial announcements to feeding announcements, to squeaks and chirps that serve to identify them to other birds -- and to observant humans. Owls, crows, chickadees, whip-poor-wills and many others are readily recognized as far away as they can be heard. With practice, the various notes of most birds can become as familiar as the caw of the crow. Go to IndexBirding as a hobbyThe hobby of birding, often called birdwatching, is open to all, regardless of level of vision. All that is needed is a way to learn the sounds, and an open window. The person listening carefully from a window, even in the city, can soon learn a great deal about the bird populations in the area and how that and the behavior of the birds changes by season. Those in the east soon learn that tree swallows and phoebes are the first consumers of flying insects to return in the spring.Perhaps the greatest pleasure to be derived from birding is the exchanging of observations with others with like interests. Among knowledgable people, the arrival of the first tree swallow of the season, or the first phoebe is a source of shared excitement.And there is a beauty to birdsong, too. Anyone who has heard the Hermit Thrush or the Common Loon doesn't need to be told that there is music in the natural world.Eight hundred or more species of birds have been found somewhere in North America at one time or another. Some 8,000 are known worldwide. While not all these birds may be readily identified by sound, specialists feel that if they were placed anywhere in the world, they would be able to tell their location without any clues other than the voices of birds around them. Go to IndexScientific observationThe skillful observer of birds can contribute to the scientific knowledge of bird movements and to the science of ecology. Remember that miners used to carry a canary into the mines with them because birds are more sensitive to air quality than are humans. By watching the canary, the miners could tell if conditions dangerous to them were developing. So by paying attention to the behaviors and numbers of birds -- in organized bird counts and informally -- we all serve as observers of the miner's canaries of nature that let us know when dangerous conditions for humans may be developing through environmental damage. Reduced numbers of songbirds in eastern forests in recent years has reinforced the observation that the destruction of tropical forest wintering habitat and nesting habitat in our own forests may be reaching dangerous proportions. Go to IndexAn introduction to natureAnd birds may be only the starting point for the blind nature enthusiast. There are other sounds to learn that give cues to the world around. There are sounds of frogs and insects to learn that add depth and dimension to perceptions. The whisper of wind in the trees varies depending on type of tree and season of the year. Wildflowers and many trees and shrubs can be distinguished by scent; plants can be identified by feel. With practice, a person can tell something about what kind of forest he or she is in by how the leaf litter feels and sounds under foot.