bird migration bird migration regular seasonal movement north south breeding grounds species bird migrate migration carries high costs predation mortality including hunting humans driven primarily availability food occurs mainly northern hemisphere birds specific routes natural barriers mediterranean_sea caribbean_sea historically migration recorded years ago authors including homer aristotle book job species turtle recently began recording dates arrivals spring migrants finland scientific studies techniques including bird ringing satellite tracking threats migratory birds grown habitat destruction especially sites structures power lines wind farms arctic holds long distance migration record birds travelling arctic breeding grounds year species circle earth flying southern oceans migrate northern breeding grounds southern ocean shorter common including mountains timing migration controlled primarily changes day length migrating birds navigate cues sun stars earth magnetic field probably mental maps historical views records bird migration years ago ancient greek writers homer aristotle bible notes book job inquiry insight hawk spreads wings southward author wrote heavens knows seasons turtle dove swift crane time arrival aristotle noted cranes traveled marshes elder repeats aristotle observations swallow migration versus aristotle suggested birds belief persisted late listed titles papers dealing highly posthumously published natural history quoted man story found chalk cliff collapse man denied eyewitness writes found state winter country heard account worth attending early happen find frost snow immediately withdraw time favour hiding migration doubts return week warmer latitudes end eighteenth century migration explanation winter disappearance birds northern accepted history british birds volume mentions report intelligent master vessel islands saw great numbers flying northward states situation britain follows frequently night begin sides rivers pools erroneously supposed retire water describes experiment succeeded keeping alive britain years remained warm dry winters concludes experiments confirmed vienna result clearly proves fact admitted hands material instance differ birds nature life air leave country longer supply proper natural food general patterns migration regular seasonal movement north south undertaken species birds bird movements include response changes food availability habitat weather journeys termed true migration irregular invasions direction dispersal movement young away area migration marked annual non migratory birds said resident approximately world bird species long distance migrants bird populations migrate long distances common pattern involves flying north spring breed temperate arctic summer returning autumn grounds warmer regions south course southern hemisphere directions reversed land area far south support long distance migration primary motivation migration appears food example choose migrate fed winter longer days northern summer provide extended time breeding birds feed young helps birds produce larger related non migratory species remain tropics days autumn birds return warmer regions available food supply varies little season advantages offset high stress physical costs risks migration predation heightened migration falcon breeds mediterranean islands late breeding season coordinated autumn passage southbound migrants feeds young similar strategy adopted greater bat nocturnal migrants higher concentrations migrating birds sites prone parasites require heightened immune response species populations migratory known partial migration partial migration common southern continents australia non birds species partially migratory species population higher latitudes tends migratory winter lower latitude migrating birds bypass latitudes populations suitable habitats occupied example leap frog migration fully migratory species leap frog migration birds nest higher latitudes spend winter lower latitudes alternative chain migration populations slide evenly north south reversing order population common different ages sexes different patterns timing distance female migrate earlier autumn males begin birds starting broad narrows preferred routes termed routes typically follow mountain ranges coastlines rivers advantage wind patterns avoid geographical barriers large stretches open water specific routes genetically programmed learned varying degrees routes taken forward return migration different common pattern north_america clockwise migration birds flying north tend west flying south tend shift eastwards birds migrate flocks larger birds flying flocks reduces energy cost formation conserve energy need fly red knots found radar studies fly mph faster flocks flying birds fly varying altitudes migration expedition found skeletons northern black tailed bar headed recorded gps flying metres crossing time engaging highest rates climb altitude bird reports flying higher direct evidence fly low water gain altitude crossing land reverse pattern seen bird migration range bird strike aviation records united_states collisions occur bird migration limited birds fly species migrate swimming routes cover perform migration walking australia observed undertake long distance movements foot long distance migration typical image migration northern birds prey making long flights tropics species winter regions winters summer breeding grounds example pink iceland britain neighbouring countries whilst dark eyed arctic climates united_states american grounds extending american south northwestward western oregon migratory routes grounds traditional learned young migration parents ducks completely partially tropics european follows migratory trend breeding asia europe africa migration route long distance bird doesn follow straight line breeding grounds follow hooked arched line geographical barriers land birds barriers consist seas large water bodies high mountain ranges lack feeding sites lack thermal columns broad winged birds considerations barriers apply long distance land bird migration apply water birds reverse large area land bodies water offer feeding sites barrier bird feeds coastal waters avoiding barriers observed example migrating travel coast baltic_sea directly northern scandinavia similar situation occurs called north_america species western undertake long movements arctic breeding grounds warmer locations hemisphere travel longer distances tropics species migration success depends availability certain key food resources points migration route gives migrants opportunity refuel leg voyage examples important locations delaware bay bar tailed longest known non stop flight flying alaska new_zealand non breeding areas prior migration percent stored fat fuel journey migration similar pattern black breeding temperate northern hemisphere varying distances south northern winter arctic longest distance migration bird sees daylight moving arctic breeding grounds non breeding areas arctic banded chick islands british east coast reached melbourne australia months sea journey birds breed southern hemisphere migrate north southern winter species mainly order great southern oceans circle globe ride outside breeding season spread widely large areas open ocean food available longest distance migrants nesting migrate breeding colony norway journey reverse long lived birds cover enormous distances lives record breaking calculated flown million million miles year lifespan migration large broad winged birds rely thermal columns rising hot air enable include birds prey eagles birds migrate daytime migratory species groups great difficulty crossing large bodies water form land birds maintain active flight long distances mediterranean seas present major obstacle soaring birds cross points massive numbers large pass areas migration times common species european honey counted hundreds thousands autumn barriers mountain ranges cause particularly large migrants notable factor central american migratory heaviest migratory funnels earth avoiding flying black_sea surface high mountains hundreds thousands soaring birds funnel area city georgia birds prey honey migrate lose weight migration explain forage migration smaller birds prey active flight hawks nocturnal migration smaller birds smaller birds including migrate large distances usually night land morning feed days resuming migration birds referred passage migrants regions occur short origin destination nocturnal migrants minimize predation avoid feed day cost nocturnal migration loss sleep migrants able alter quality sleep compensate loss short distance migration long distance migrants appear genetically programmed respond changing day length species short distances need timing mechanism instead moving response local weather conditions mountain breeders white escape cold higher ground species coast south species like migratory britain continental europe moving lives short distance migrants evolutionary origins long distance migrants family common species southern hemisphere origins progressively shortened return migration stay northern hemisphere species long distance migratory relatives effectively moving response winter weather loss usual winter food enhanced breeding opportunities tropics little variation length day year warm food supply migration occurs tropical birds evidence enables migrants obtain preferred foods fruits migration common mountains worldwide dispersal circumstances good breeding season followed food source failure following year lead large numbers species far normal range bohemian unpredictable variation annual numbers major arrivals britain nineteenth century years red widespread invasions england noted bird migration primarily entirely phenomenon land birds high northern latitudes food scarce winter leave areas south including continental larger contrast species likely migrate large area ocean islands suitable nest physiology control control migration timing response genetically controlled appear primitive trait present non migratory species birds ability navigate orient migration complex phenomenon include programs learning timing primary cue migration changes day length changes related changes birds period migration birds display higher activity german migratory described changes increased fat deposition occurrence cage raised birds environmental cues shortening day falling temperature pointed role programs controlling bird birds display flight direction corresponds migratory direction nature changing direction roughly time wild change course species considerable sexual males tend return earlier breeding sites females termed orientation navigation navigation based variety senses birds shown use sun compass sun direction involves need making compensation based time navigation shown based combination abilities including ability detect magnetic fields use visual landmarks cues long distance migrants believed disperse young birds form potential breeding sites favourite sites site attachment high site fidelity visiting sites year year ability birds navigate fully explained programming help responses environmental cues ability successfully perform long distance probably fully explained accounting ability birds recognize habitats form mental maps satellite tracking day migrating honey shown older individuals better making wind drift migratory birds use electromagnetic tools find destinations entirely innate relies experience young bird migration flies correct direction according earth magnetic field know far journey radical pair mechanism chemical reactions special photo sensitive long affected field works daylight hours use position sun way stage bird position boy scout compass map grows accustomed journey capabilities use experience learns landmarks mapping system tell bird strong field birds migrate northern southern regions magnetic field strengths different latitudes let interpret radical pair mechanism accurately let know reached destination connection eye cluster active orientation suggesting birds actually able magnetic field earth migrating birds lose way appear outside normal ranges flying past destinations spring birds returning breeding areas end north intended certain areas location famous birds examples canada england reverse migration genetic programming young birds fails work properly lead turning thousands kilometres range drift migration birds blown course wind result falls large numbers migrants coastal sites related phenomenon called involves birds region joining similar birds different breeding region common winter grounds migrating new population especially common shift migration conditioning possible teach migration route flock birds example introduction schemes trial canada aircraft teach safe migration routes reintroduced cranes adaptations birds need alter order meet demands migration storage energy accumulation fat control sleep nocturnal migrants require special adaptations addition feathers bird suffer wear tear require timing usually year twice varies species prior moving winter grounds prior returning breeding grounds apart adaptations migration requires changes flying flocks reduce energy migration risk predation evolutionary ecological factors migration birds highly believed developed independently agreed adaptations necessary migration genetic control authors argued genetic change necessary migratory behavior develop species genetic framework migratory behavior exists nearly explains rapid appearance migratory behavior recent glacial maximum theoretical analyses increase flight distance aerodynamic grounds bird loads food cross long barrier flies efficiently species migratory routes reflect historical range expansions far optimal ecological terms example migration continental populations fly far east north_america turning south florida reach northern south_america route believed consequence range expansion occurred years ago caused differential wind conditions predation risk factors climate change large scale climatic changes experienced past expected effect timing migration studies shown variety effects including timing changes migration breeding population variations ecological effects migration birds aids movement species including turn carry micro organisms including concern human health global spread bird migration studied possible mechanism disease transmission found present special risk import pet domestic birds greater threat maintained birds lethal effects spread migrating birds birds role dispersal plants predators advantage concentration birds migration greater bats feed nocturnal migrating birds prey migrating study techniques early studies timing migration began finland collecting dates arrivals spring migrants bird migration routes studied variety techniques including oldest marking marked nick england scientific ringing pioneered techniques include radar satellite tracking stable hydrogen oxygen carbon nitrogen establish migratory sites breeding grounds stable methods establish migratory rely spatial differences bird diet incorporated tissues like feathers growing tissues claws muscle blood approach identify migration intensity makes use upward pointing record nocturnal contact calls flocks flying overhead analyzed laboratory measure time frequency species older technique migration involves observing face moon moon counting flocks birds fly night orientation behaviour studies traditionally carried variants setup known funnel consists circular cage covered glass wire screen sky visible setup placed controls environmental cues orientation behaviour bird inside cage studied distribution marks bird leaves walls cage approaches studies use direction bird horizon threats conservation human activities threatened migratory bird species distances involved bird migration mean cross political boundaries countries conservation measures require international cooperation international treaties signed protect migratory species including migratory bird treaty act migratory agreement concentration birds migration species risk spectacular migrants gone extinct passenger migration enormous flocks mile wide sky miles long taking days pass significant areas include stop sites breeding territories capture recapture study migrants high fidelity breeding sites similar strict association stop sites hunting migration routes threatens bird species populations cranes india declined hunting route particularly afghanistan birds seen favourite grounds national park structures power lines wind farms offshore oil known affect migratory birds migration hazards include pollution storms habitat destruction migration routes denying migrants food points example key habitat migration destroyed 1950s
Bird migration