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All About Migration--North American Birds

What makes birds migrate?  It's a fact that birds have an enormous advantage over all other creatures, simply because they have feathered wings.  When food is scarce, they can quickly travel to more abundant sources and easily locate their prey from the air. When winter descends, birds have little trouble relocating to warmer climates and more plentiful food sources. The combination of these abilities and events over a long period of time eventually culminated in large populations of birds leaving their summer grounds en-masse for more hospitable climates when winter approaches.  This is the phenomenon we know as migration.

Some birds never migrate, but for birds that do, it is not choice but a programmed response to environmental cues. In North America there are about 350 migrating species, 250 of which are considered Neo-tropical, meaning that they winter in Mexico, Central and South America as well as the West Indies. It is generally accepted that a change in day length causes significant changes in a migrating bird's brain. Among other things, this internal change stimulates a bird's appetite in order to build up an enormous storage of fat, induces a sense of restlessness and encourages the tendency to flock together. There is safety in numbers during this long, stressful journey. It's an interesting fact that the farther north a bird's summer range is, where seasonal day length is most pronounced, the more likely it is that the species will migrate. Near the equator, where the days and nights are always of equal length, there is a much lower percentage of migrating birds. The change in daylight in a bird's winter range triggers additional hormonal changes that also prepare the bird for breeding when its return northward migration is completed.

Migratory birds are different from non-migratory birds in other ways, too. All birds have hollow bones, insulating feathers, and unique "wishbone" which powers their wings with strong pectoral muscles, and lungs which are kept constantly inflated by extra air sacs not found in other creatures. However, migratory birds tend to have much larger pectoral muscles with more blood vessels, which make them much more efficient at producing and using energy. Their wings tend to be longer and more pointed. Even their blood is different. While all birds have high concentrations of red blood cells for efficient oxygen dispersal, some migratory birds actually have two kinds of hemoglobin in their red blood cells that carry oxygen through their bodies in different ways. This is what allows them to fly at high altitudes where the oxygen levels are very low. Another interesting difference about some migrating birds is that their activity period shifts from daytime to nighttime right before they begin to leave. Traveling at night and at high altitudes, birds can take advantage of the lack of predators, a calm air mass and have a lesser chance of overheating or dehydrating. Most songbirds and shorebirds migrate at night.

In North America there are four major migration routes, known as the Atlantic, Mississippi, Central and Pacific Flyways. A flyway can generally be described as a broad geographical area of travel consisting of hundreds of widely diverse, individual migration routes. No two species of birds will travel exactly the same route from beginning to end. As these routes continue further south, they tend to blend and converge. In Panama, all the North American Flyways merge into one and then spread out again throughout South America. Of course, some birds have already reached their winter grounds long before the flyways merge, while others will continue farther south to reach theirs. Flyways tend to follow major geographical landmarks, such as the Atlantic and Pacific coasts, along the Rocky Mountains and the Mississippi River. For the most part, migration routes and the Flyways are along areas with no major mountains or water areas to cross and offer the longest line of sight. This brings us to the next factor in migration; navigation.  Migrating birds navigate with a combination of different methods. Along with sighting visual landmarks, following rivers, coastlines and mountains, birds also have a mineral called magnetite in their brains. It is thought that this mineral enables a bird to monitor the earth's magnetic fields to guide them north and south. Generally it is known that birds migrating by day also use the sun as a reference point, while birds migrating by night use the stars. And it's probable that birds follow other flocks. What is not known is how birds compensate for and overcome changing constellations, sunless days, interferences in magnetic fields caused by radio towers and the like. Somehow the birds are able to recalibrate their magnetic compasses based on the visual cues that are available to them at different times. 

At some point in the distant past, survival of the fittest determined that some birds were more likely to thrive if they migrated rather than remaining in the same area year round. However, migrating birds encounter many more obstacles now than even a hundred years ago. Among these include loss of nesting habitat along the flyways as grasslands are converted to croplands, loss of coastal resting areas, loss of rainforests in the South Americas, interference by planes, skyscrapers and towers to name just a few. All of this has shown to cause a significant decline in some migratory bird species. However, there is good news. Working from information gathered by the BBS (Bird Breeding Survey) and other sources, the National Fish and Wildlife Foundation began an extensive program in 1991 called Partners in Flight. Involving many organizations on local, state and federal levels, as well as conservation groups, individuals and philanthropic groups, this program is dedicated to the preservation of migrating birds, providing research and millions of dollars to the cause. As a result, they have been instrumental in the protection of avian habitats and strive to improve education, research, and the management of migratory birds.  

Many backyard birders find themselves located in a flyway zone or on at least one migratory route. Resting places along these routes are vital to traveling birds. Sometimes they will stop for only a day, but many times birds need several days in their resting location to build up enough fuel for the next leg of the trip. If you wish to lend a helping hand to these birds, it's easy to provide the basic necessities; food, water, and shelter . Shelter can be ornamental shrubbery or even branches from dead trees piled in a corner of your property. If you have a brook or creek that has open water in the winter time, you won't need to worry about a water supply, but if not, you might want to consider heated water in the form of a bird bath heater or even a bath that has a built-in heater . Food choices are endless. Seed blends , fruit , suet or even stale baked goods will be well received. If you are lucky enough to live near a flyway or migratory route, spring and fall are very exciting times!

--Roxanne Brune

INTERESTING FACTS AND OTHER LINKS TO SOME MIGRATION ARTICLES

Scientists have suspected for a while that birds navigate their way around the world while migrating south using the Earth's magnetic field as a guide. However, the mechanism by which this happens is not understood. New research is suggesting that birds are able to “see” the Earth's magnetic field as if it were a pattern of colors by the method of quantum entanglement. The idea that birds have the ability to see the invisible magnetic fields all around us as different colors is fascinating to think about.

Originally Posted: http://thetechjournal.com/science/quantum-mechanics-may-help-birds-migrate-south-for-the-winter.xhtml#ixzz15qgHYoTD

 

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MIGRATION OF ANIMALS

The Columbia Encyclopedia, Sixth Edition | 2008 | The Columbia Encyclopedia, Sixth Edition. Copyright 2008 Columbia University Press. Copyright

Migration of animals are movements of animals in large numbers from one place to another. In modern usage the term is usually restricted to regular, periodic movements of populations away from and back to their place of origin. A single round trip may take the entire lifetime of an individual, as with the Pacific salmon ; or an individual may make the same trip repeatedly, as with many of the migratory birds and mammals. The animals may travel in groups along well-defined routes; or individuals may travel separately, congregating for breeding and then spreading out over a wide feeding area, as do some of the seals .

Types of Migration

Seasonal migrations occur in many species of insects, birds, marine mammals, and large herbivorous mammals. These migrations often provide the animals with more favorable conditions of temperature, food, or water. Many birds and a few bats of cold and temperate regions migrate to warmer areas during the winter. Herbivores of cold regions, such as wapiti (elk), caribou , and moose , have summer and winter ranges; many herbivores of warm regions, such as the African antelopes , migrate seasonally to avoid drought. These migrations may involve a change of latitude, of altitude, or both.

In many cases the chief function of seasonal migration is to provide a suitable place for reproduction, which may not be the place most suitable for the feeding and other daily activities of adults. Hundreds of thousands of gnus (wildebeests) of E Africa take part in annual migrations to calving grounds. Many fishes migrate to spawning grounds, and in some cases this involves a change from saltwater to freshwater (e.g., salmon) or vice versa (e.g., freshwater eels ). Sea turtles , seals, and many sea birds come ashore to breed, and most amphibians gather near water at the breeding season. Fur seals and many whales make ocean voyages of thousands of miles to their breeding grounds, the former coming ashore on islands. Such migration is seriously affected by the increasing rate of destruction of natural habitats.

The term emigration refers to irregular movements out of an area, with no return. When such emigration is the result of sudden, explosive population increase, it is called an irruption. Irruptions are common among small rodents, notably lemmings , and various species of birds and insects. The mass movements of the so-called migratory locusts of N Africa ( Locusta ) and North America ( Melanoplus ) are actually irruptions; however, the N African desert locust ( Schistocerca ) makes true migrations between its winter and summer breeding grounds.

Another type of one-way travel is the regular dispersal of the young of most species. The simplest type of regular migration is the diurnal movement of some marine microorganisms from one depth to another in response to light changes. Certain marine invertebrates, such as the palolo worm (see Annelida ), have a monthly migration pattern influenced by the phases of the moon.

Initiation of Migration

Various factors determine the initiation of migration. In some cases external pressures—temperature, drought, food shortage—alone may cause the animals to seek better conditions. For example, most of the mule deer of Yellowstone Park, Wyo., migrate between summer and winter pastures, but those living near hot springs, where grazing is available all year, do not. In many species migration is initiated by a combination of physiological and external stimuli. In birds the migratory instinct is related to the cycle of enlargement of the reproductive organs in spring and their reduction in fall. Experiments have shown that variation in day length is the chief external stimulus for this cycle: light received by the eye affects production of a hormone by the anterior pituitary gland, which stimulates growth of the reproductive organs.

Orientation and Navigation

Much work has been done on orientation and navigation in migrating animals, although the subject is still not well understood. Studies of salmon indicate that they depend on the olfactory sense to locate and return to their stream of origin. Herbivorous mammals often follow well-established trails and probably also use their sense of smell. Bats, whales, and seals use echolocation to navigate in the dark or underwater; in addition, some whales appear to take visual bearings on objects on the shore in their migrations.

Migratory birds are believed to use the stars, sun, and geographic features as guides. The probability that stellar navigation is used has been strengthened by experiments in planetariums indicating that birds navigate at least in part by the stars. Night-migrating birds are sometimes disoriented in prolonged heavy fog. Day-flying birds navigate by the sun and also make some use of geographic features, particularly of shorelines. It has long been proposed that birds perceive the direction of the earth's magnetic field and use it for navigation, but experimental evidence for that hypothesis is inconclusive. Most migratory birds travel within broad north-south air routes known as flyways. There are four major flyways in North America, called the Pacific, central, Mississippi , and Atlantic flyways. The space within the flyway used by a particular group of birds is called a corridor. Bird migration is not always in a north-south direction. Many European birds migrate in an east-west direction, wintering in the more temperate British Isles, and many mountain-dwelling birds descend to lower altitudes in winter. The breeding grounds of a bird species are regarded as its home territory. Some migratory birds winter only a few hundred miles from their breeding grounds, while others migrate between the cold or temperate zones of the two hemispheres. The longest journey is made by the arctic tern , which alternates between the Arctic and the Antarctic.

The monarch butterfly has a north-south migration pattern that resembles that of many birds. One monarch population that inhabits northeastern and midwestern North America averages c.12 mph (19 kph) as it heads for the winter to Mexico 's Sierra Madre mountains. Monarchs start the return trip in the spring, but they breed along the way and then die; the new generation completes the journey.

Tools for Studying Migration

The movements of migrating animals are often studied by tagging individuals. Bird banding has been carried on extensively since the 1920s; more recently there has been tagging of fishes, butterflies, and marine mammals. Use is now made of radar, sonar, and radio for following migrations, particularly those of marine animals. Radio transmitters attached to whales or seals emit signals that can be picked up by weather satellites at regular intervals.

Bibliography

See R. R. Baher, The Evolutionary Ecology of Animal Migration (1978); D. J. Aidley, Animal Migration (1981)

"migration of animals." The Columbia Encyclopedia, Sixth Edition . 2008. Retrieved November 20, 2010 from Encyclopedia.com: http://www.encyclopedia.com/doc/1E1-migranmls.html

 

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Tyler Audubon Society is devoted to the enjoyment and safekeeping of the natural world. Through the participation in birding, education and conservation ventures, we encourage East Texans to join us in our mission.

The primary objective of the Tyler Audubon Society is to create an awareness of the natural world's beauty and problems by promoting an appreciation of birds, other wildlife and habitat,  to promote an awareness of the environmental problems of the past, present and future, and to find solutions for these problems.