Abstract- The purpose of this term paper is to give the description of Electromagnetic waves application in bird migration. It also include the detail study of EM waves along with its applied application specially in field of Electronics engineering .Since it is the outcome of the research and analysis of the topic so it not only includes the class notes concept rather modified and future aspects are also taken under consideration.
Electricity can be static, like what holds a balloon to the wall or makes your hair stand on end. Magnetism can also be static like a refrigerator magnet. But when they change or move together, they make waves - electromagnetic waves. Electromagnetic waves are formed when an electric field (shown as blue arrows) couples with a magnetic field (shown as red arrows). The magnetic and electric fields of an electromagnetic wave are perpendicular to each other and to the direction of the wave.Â James Clerk Maxwell and Heinrich Hertz are two scientists who studied how electromagnetic waves are formed and how fast they travel.Â
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Fig. 1 EM waves
II. ELECTROMAGNETIC WAVES
A: Electromagnetic radiationÂ
Often abbreviatedÂ E-M radiationÂ orÂ EMR is aÂ phenomenonÂ that takes the form ofÂ self-propagatingÂ wavesÂ in a vacuumÂ or inÂ matter. It consists ofÂ electricÂ andÂ magnetic fieldÂ components whichÂ oscillateÂ in phase perpendicular to each other and perpendicular to the direction of energyÂ propagation. Electromagnetic radiation is classified into several types according to theÂ frequencyÂ of its wave; these types include (in order of increasing frequency and decreasing wavelength):Â radio waves,Â microwaves,Â terahertz radiation,Â infrared radiation,Â visible light, ultraviolet radiation,Â X-raysÂ andÂ gamma rays. A small and somewhat variable window of frequencies isÂ sensedÂ by theÂ eyesÂ of variousÂ organisms; this is what is called theÂ visible spectrum, orÂ light.
EM radiation carriesÂ energyÂ andÂ momentumÂ that may be imparted toÂ matterÂ with which it interacts.
Fig. 2 Electromagnetism
Electromagnetic wavesÂ were first postulated byÂ James Clerk MaxwellÂ and subsequently confirmed byÂ Heinrich Hertz. Maxwell derived aÂ wave form of the electric and magnetic equations, revealing the wave-like nature of electric and magnetic fields, and their symmetry. Because the speed of EM waves predicted by the wave equation coincided with the measuredÂ speed of light, Maxwell concluded thatÂ lightÂ itself is an EM wave.
According toÂ Maxwell's equations, a spatially-varyingÂ electric fieldÂ generates a time-varyingÂ magnetic fieldÂ andÂ vice versa. Therefore, as an oscillating electric field generates an oscillating magnetic field, the magnetic field in turn generates an oscillating electric field, and so on. These oscillating fields together form an electromagnetic wave.
AÂ quantum theoryÂ of the interaction between electromagnetic radiation and matter such as electrons is described by the theory ofÂ quantum electrodynamics.
TheÂ physicsÂ of electromagnetic radiation isÂ electrodynamics.Â ElectromagnetismÂ is the physical phenomenon associated with the theory of electrodynamics. Electric and magnetic fields obey the properties ofÂ superpositionÂ so that a field due to any particular particle or time-varying electric or magnetic field will contribute to the fields present in the same space due to other causes: as they areÂ vectorÂ fields, all magnetic and electric field vectors add together according to vector addition..
Fig. 3 Formation of EM waves
Since light is an oscillation it is not affected by travelling through static electric or magnetic fields in a linear medium. However in nonlinear media, such as someÂ crystals, interactions can occur between light and static electric and magnetic fieldsÂ - these interactions include theÂ Faraday EffectÂ and theÂ Kerr effect.
In refraction, a wave crossing from one medium to another of differentÂ densityÂ alters its speed and direction upon entering the new medium. The ratio of the refractive indices of the media determines the degree of refraction, and is summarized byÂ Snell's law. Light disperses into a visibleÂ spectrumÂ as light is shone through a prism because of the wavelength dependent refractive index of the prism material (Dispersion).
Fig.4 Cross field in EM Waves
EM radiation exhibits both wave properties andÂ particleÂ properties at the same time (seeÂ wave-particle duality). Both wave and particle characteristics have been confirmed in a large number of experiments. Wave characteristics are more apparent when EM radiation is measured over relatively large timescales and over large distances while particle characteristics are more evident when measuring small timescales and distances
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WAVE MODEL: An important aspect of the nature of light isÂ frequency. The frequency of a wave is its rate of oscillation and is measured inÂ hertz, theÂ SIÂ unit of frequency, where one hertz is equal to one oscillation perÂ second. Light usually has a spectrum of frequencies which sum together to form the resultant wave. Different frequencies undergo different angles of refraction..A wave consists of successive troughs and crests, and the distance between two adjacent crests or troughs is called theÂ wavelength. Waves of the electromagnetic spectrum vary in size, from very long radio waves the size of buildings to very short gamma rays smaller than atom nuclei. Frequency is inversely proportional to wavelength, according to the equation:
WhereÂ vÂ is the speed of the wave (cÂ in a vacuum, or less in other media),Â fÂ is the frequency and Î» is the wavelength. As waves cross boundaries between different media, their speeds change but their frequencies remain constant.
PARTICLE: Electromagnetic radiation has particle-like properties as discrete packets of energy, orÂ quanta, calledÂ photons. The frequency of the wave is proportional to the particle's energy. Because photons are emitted and absorbed by charged particles, they act as transporters ofÂ energy. The energy perÂ photonÂ can be calculated from theÂ Planck-Einstein equation:
WhereÂ EÂ is the energy,Â hÂ isÂ Planck's constant, andÂ fÂ is frequency. As a photon is absorbed by anÂ atom, it excites anÂ electron, elevating it to a higherÂ energy level. If the energy is great enough, so that the electron jumps to a high enough energy level, it may escape the positive pull of the nucleus and be liberated from the atom in a process calledÂ photo ionisation. Conversely, an electron that descends to a lower energy level in an atom emits a photon of light equal to the energy difference. Since the energy levels of electrons in atoms are discrete, each element emits and absorbs its own characteristic frequencies.
D: Electromagnetic Spectrum
Generally, EM radiation (the designation 'radiation' excludes static electric and magnetic andÂ near fields) is classified by wavelength intoÂ radio,Â microwave,Â infrared, theÂ visible regionÂ we perceive as light,Â ultraviolet,Â X-raysÂ andÂ gamma rays. Arbitrary electromagnetic waves can always be expressed byÂ Fourier analysisÂ in terms of sinusoidal monochromatic waves which can be classified into these regions of the spectrum.
The behaviour of EM radiation depends on its wavelength. Higher frequencies have shorter wavelengths, and lower frequencies have longer wavelengths. When EM radiation interacts with single atoms and molecules, its behaviour depends on the amount of energy per quantum it carries.
Fig. 5 Electromagnetic spectrum
E: Application of EM Waves
RADIOWAES: Yes, It is used for ground wave, sky wave propogation, television communication an all depending upon the frequency range.
MICROWAVES: Used in RADAR system for air craft navigation. Microwaves ovens are used for cooking .In study of atomic and molecular structure.
INFRARED RAYS: Used in physical therepy.to produce electrical energy for satellite using solar energy. In photo graph. In detecting secretes writings.
VISIBLE LIGHT: This help in viewing surrounding by the light reflected or emitted by a object.
ULTRAVOILET RAYS: Is the source of vitamin D. To destroy bacteria. Study of molecular structure.
X-RAYS: Used in medical purpose. In detection of flaws and cracks in engineering. In radiotherapy. In research. In detection of explosives an all.
GAMMA RAYS: In treatment of cancer and tumours. To produce nuclear reactions. Study of molecular structure.
F: EM Waves in applied Electronics
In Satellites communication.
In Microwave communication.
In Mobile communication.
In broadcasting technology.
In Bluetooth communication
In Optical fibre communication.
In IR communication.
In Infrared imaging.
Bird migrationÂ refers to the regular (and often seasonal) journeys to and from a given area undertaken by all or part of aÂ birdÂ population. Not all birdÂ speciesÂ (or even populations within the same species) are migratory. In contrast to more irregular movements such as emigration,, andÂ invasion, which are made in response to changes in food availability, habitat, or weather, bird migration is marked by its cyclical pattern.
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Fig. 6 Bird migration
.The primary advantage of migration is energetic. In the Northern Hemisphere, the long days of summer provide greater opportunities for breeding birds to feed their young. As the days shorten in autumn, the birds return to warmer regions where the available food supply varies little with the season. Migratory birds have evolved to undertake long-distance flights efficiently, and they undergo physiological changes (such as an accumulation ofÂ fatÂ stores) prior to migration that minimize the energetic cost of flight.
Migrations typically occur along established routes called "flyways." The migrating species often return to the area of their birth to breed. The birds are guided by innate behaviours (including hormonalÂ signals) that enable them to know when to depart and that orient them toward a specific location over long distances. However, they also remain flexible to environmental conditions, such as food supply and temperature, which may fluctuate .Bird migration has largerÂ ecologicalÂ implications that underscore the interconnectedness of life: Migratory cycles are closely attuned to seasonal food productivity cycles, which leads to a mutual gain for both the migrating species and the ecosystems in which they participate. Migratory birds are able to settle in areas where life is not tenable year-round, while the food resources of some regions would not be adequately utilized without the seasonal presence of migrating populations
A: Why does bird migrate?
One textbook explanation suggests either eating fruit or living in non-forested environments were the precursors needed to evolve migratory behaviour.
Not so, report a pair of ecologists from The University of Arizona in Tucson. The pressure to migrate comes from seasonal food scarcity.
"It's not just whether you eat insects, fruit, nectar or candy bars or where you eat them -- it matters how reliable that food source is from day-to-day," said W. Alice Boyle. "For example, some really long-distance migrants like arctic terns are not fruit-eaters." Boyle, an adjunct lecturer in UA's department of ecology and evolutionary biology and co-author Courtney J. Conway, a UA assistant professor of natural resources and a research scientist with the U.S. Geological Survey, report their findings in the March 2007 issue of American Naturalist.
To figure out the underlying pressures that drive some birds to leave home for the season, the team wanted to examine a related set of species and compare their size, food type, habitat, migratory behaviour and whether they fed in flocks. The technique allowed the scientists to sort out whether a bird was migratory because that's what species on their side of the family tree always did or whether the bird's travel habits had some ecological correlates. Food scarcity was the number one issue that predicted a species' migratory behaviour, the team found. Boyle said, "Food availability is the underlying process, not diet and habitat."
Fig.7 Migration at sunset
One strategy for dealing seasonal changes in food availability is migration. The team also found that species that forage in flocks are less likely to migrate."If you are faced with food scarcity, you have two options," Boyle said. "You can either forage with other birds or you can migrate." When birds band together to search for food, the group is more likely to find a new patch of food than is one lone individual, she said. "Flocking can be an alternative way to deal with food shortages."
Conway is also a research scientist with the U.S. Geological Survey. The two showed the pressure to migrate comes from seasonal food scarcity. It's the first time the technique called phylogenetic independent contrasts has been used to identify the causes of bird migration. "It's not just whether you eat insects, fruit, or candy bars, or where you eat them -- it matters how reliable that food source is from day-to-day," Boyle said. "For example, some really long-distance migrants like Arctic Terns are not fruit-eaters."
B: General pattern of migration
Many birds migrate long distances. The most common pattern involves flying north to breed in the temperate or Arctic summer and returning to wintering grounds in warmer regions to the south. The primary advantage of migration is energetic. The longer days of the northern summer provide greater opportunities for breeding birds to feed their young. The extended daylight hours allowÂ diurnalÂ birds to produce largerÂ clutchesÂ than related non-migratory species that remain in the tropics year-round. As the days shorten in autumn, the birds return to warmer regions where the available food supply varies little with the season. These advantages offset the high stress, energetic costs, and other risks of the migration. Predation can be heightened during migration; Migration often is concentrated along well-established routes known as flyways, which are shaped by geographical, ecological, and even meteorological factors. Flyways typically follow mountain ranges or coastlines, and may take advantage of updrafts and other wind patterns, or avoid geographical barriers, such as (in the case of land birds) large stretches of open water.
Theoretical analyses, summarized by Amersham (2001), show that detours that increase flight distance by up to 20 percent will often be adaptive onÂ aerodynamicÂ grounds-a bird that loads itself with food in order to cross a long barrier flies less efficiently. However, some species show circuitous migratory routes that reflect historical range expansions and are far from optimal in ecological terms. An example is the migration of continental populations of Swanson's Thrush, which fly far east across Predation can be heightened during migration; Migration often is concentrated along well-established routes known as flyways, which are shaped by geographical, ecological, and even meteorological factors. Flyways typically follow mountain ranges or coastlines, and may take advantage of updrafts and other wind patterns, or avoid geographical barriers, such as (in the case of land birds) large stretches of open water.
Fig.9 Route of migration
North America before turning south viaÂ FloridaÂ to reach northernÂ South America; this route is believed to be the consequence of a range expansion that occurred about 10,000 years ago. Detours may also be caused by differential wind conditions, predation risk, or other factors.
Fig.10 Long distance migration pattern
C: How do birds migrate?
The essential skills of bird migration are orientation - knowing north from south, and east from west - and navigation, having some sort of "map" to establish the location you're aiming for. Birds usually orient themselves by observing the sun and the stars - although some can also sense Earth's magnetic field. Orientation is not enough by itself: to find your way to the right location, you also need navigation - in this case using a mental map of where you're going. The mental map may have inherited and learned components, Temple says.
"The inherited map plays a role in the many birds that do a first migration completely on their own, without associating with other individuals. Other species learn the appropriate migration route by following experienced birds, or even the ultra-light airplanes that have guided hand-reared whooping cranes."Birds also employ redundant orientation systems," Temple says. "They will normally use the most accurate directional clue, but will fall back on a less accurate clue if necessary. If celestial navigation is the primary way to orient, and it's overcast, they may shift to geomagnetism, landmarks, or other, less accurate techniques that will still get the job done."
Within a species not all populations may be migratory and this is termed as partial migration. Partial migration is very common in the southern continents; in Australia, 44% of non-passerine birds and 32% of passerine species were partially migratory. In some species the population at higher latitudes tend to be migratory and will often winter at lower latitude past the latitudes where other populations may be sedentary, with suitable wintering habitats already occupied, and this is termed asÂ leap-frog migration.Â
D: Application of EM waves in bird migration
Migratory birds may use twoÂ electromagneticÂ tools to find their destinations: one that is entirely innate and another that relies on experience. A young bird on its first migration flies in the correct direction according to the Earth'sÂ magnetic field, but does not know how far the journey will be. It does this through a radical pair mechanism whereby chemical reactions in specialÂ photo pigmentsÂ sensitive to long wavelengths are affected by the field. Note that although this only works during daylight hours, it does not use the position of the sun in any way.
At this stage the bird is similar to aÂ boy scoutÂ with a compass but no map, until it grows accustomed to the journey and can put its other facilities to use. With experience they learn various landmarks and this "mapping" is done byÂ magnetite'sÂ in the trigeminal system, which tell the bird how strong the field is. Because birds migrate between northern and southern regions, the magnetic field strengths at differentÂ latitudesÂ let it interpret the radical pair mechanism more accurately and let it know when it has reached its destination. More recent research has found a neural connection between the eye and "Cluster N", the part of the forebrain that is active during migration orientation, suggesting that birds may actually be able toÂ seeÂ the magnetic field of the earth.
Migration is based on a variety of senses. Many birds have been shown to use a sun compass. Using the sun for direction involves the need for making compensation based on the time. Navigation has also been shown to be based on a combination of other abilities including the ability to detect magnetic fields, use visual landmarks as well as olfactory cues
Fig.10 Orientation and Navigation by EM Waves (Earth field effects)
Birds usually orient themselves by observing the sun and the stars - although some can also sense Earth's magnetic field. Orientation is not enough by itself: to find your way to the right location, you also need navigation - in this case using a mental map of where you're going. The mental map may haveÂ inherited and learned components, Temple says."The inherited map plays a role in the many birds that do a first migration completely on their own, without associating with other individuals, using a well-developed innate map,".
Other species learn the appropriate migration route by following experienced birds, or even the ultra-light airplanes that have guided hand-reared whooping cranes."Birds also employ redundant orientation systems," Temple says. "They will normally use the most accurate directional clue, but will fall back on a less accurate clue if necessary. If celestial navigation is the primary way to orient, and it's overcast, they may shift to geomagnetism, landmarks, or other, less accurate techniques that will still get the job done."
The E: Other key factors of bird migration
MONOTORING AND CONTROLLING :control of migration, its timing and response are genetically controlled and appear to be a primitive trait that is present even in non-migratory species of birds. The ability to navigate and orient them during migration is a much more complex phenomenon which may include both endogenous programs as well as learning. The primary physiological cue for migration are the changes in the day length. These changes are also related to hormonal changes in the birds.
In the period before migration, many birds display higher activity OR (German: migratory restlessness) as well as physiological changes such as increased fat deposition. The occurrence of even in cage-raised birds with no environmental cues (e.g. shortening of day and falling temperature) has pointed to the role of circannualÂ endogenÂ programming in controlling bird migrations. Caged birds display a preferential flight direction that corresponds with the migratory direction they would take in nature, even changing their preferential direction at roughly the same time their wild co specifics change course.
EVOLUTIONARY AND ECOLOGIAL FACTORS: Whether a particular species migrates depends on a number of factors. The climate of the breeding area is important, and few species can cope with the harsh winters of inlandÂ CanadaÂ or northernÂ Eurasia. Thus the partially migratory BlackbirdÂ Tarsus merleÂ is migratory inÂ Scandinavia, but not in the milder climate of southern Europe. The nature of the staple food is also significant. Most specialist insect eaters outside the tropics are long-distance migrants, and have little choice but to head south in winter. Sometimes the factors are finely balanced. TheÂ WhinchatÂ Sax cola RobertaÂ of Europe and theÂ Siberian StonechatÂ Sax cola MauraÂ of Asia are long-distance migrants wintering in the tropics, whereas their close relative, theÂ European StonechatÂ Sax cola rub colaÂ is aÂ resident birdÂ in most of its range, and moves only short distances from the colder north and east. A Theoretical analyses, summarized by Amersham (2001), show that detours that increase flight distance by up to 20% will often be adaptive onÂ aerodynamic grounds - a bird that loads itself with food in order to cross a long barrier flies less efficiently.
However some species show circuitous migratory routes that reflect historical range expansions and are far from optimal in ecological terms. An example is the migration of continental populations ofÂ Swanson's Thrush, which fly far east acrossÂ North AmericaÂ before turning south viaÂ FloridaÂ to reach northernÂ South America; this route is believed to be the consequence of a range expansion that occurred about 10,000 years ago. Detours may also be caused by differential wind conditions, predation risk, or other factors.
STUDY TECNIQUES: Bird migration has been studied by a variety of techniques of whichÂ ringingÂ is the oldest. Colour marking, use ofÂ radar,Â satellite trackingÂ and stable Hydrogen (or Strontium)Â isotopesÂ are some of the other techniques used to study migration. An approach to identify migration intensity makes use of upward pointing microphones to record the nocturnal contact calls of flocks flying overhead. These are then analyzed in a laboratory to measure time, frequency and species.
Fig.11 Emlen Funnel
Studies of orientation behaviour have been traditionally carried out using variants of a setup known as theÂ Emlen funnelÂ which consists of a circular cage with the top covered by glass or wire-screen so that either the sky is visible or the setup is placed in a planetarium or with other controls on environmental cues. The orientation behaviour of the bird inside the cage is studied quantitatively using the distribution of marks that the bird leaves on the walls of the cage. Emlen funnel An older technique to quantify migration involves observing the face of the moon towards full moon and counting the silhouettes of flocks of birds as they fly at night. Other approaches used in pigeon homing studies make use of the direction in which the bird vanishes on the horizon.
THREATS AND CONSERVATION: Human activities have threatened many migratory bird species. The distances involved in bird migration mean that they often cross political boundaries of countries and conservation measures require international cooperation. Several international treaties have been signed to protect migratory species including the Migratory Bird Treaty Act of 1918 of the US and the African-Eurasian Migratory Water bird Agreement. The concentration of birds during migration can put species at risk. Some spectacular migrants have already gone extinct, the most notable being the Passenger PigeonÂ migratory). During migration the flocks were a mile (1.6 km) wide and 300 miles (500 km) long, taking several days to pass and containing up to a billion birds.
Other significant areas include stop-over sites between the wintering and breeding territories. A capture-recapture study of passerine migrants with high fidelity for breeding and wintering sites did not show similar strict association with stop-over sites. Hunting along the migratory route can also take a heavy toll. The populations of Siberian CranesÂ that wintered inÂ IndiaÂ declined due to hunting along the route, particularly inÂ AfghanistanÂ andÂ Central Asia. Birds were last seen in their favourite wintering grounds inÂ Keoladeo National ParkÂ in 2002. Structures such as power lines, wind farms and offshore oil-rigs have also been known to affect migratory birds. Habitat destruction by land use changes is however the biggest threat and shallow wetlands which are stopover and wintering sites.
Bird migrationÂ refers to the regular seasonal journeys undertaken by many species ofÂ birds. It includes movements of varied distances made in response to changes in foodÂ availability, habitat or weather. Migration of bird takes place by variety of senses and combination of other abilities including the ability to detect magnetic field of earth.
Thus EM waves play a vital role in bird migration, although partially but an effective one .Seeing the general trend and pattern of migration there have been several related stories about how actually birds migrate? But being a science student we can conclude that migration is completely on the basis of special organs, senses of the birds and the electromagnetic wave patterns.