A.positionedB.resolutionC.suspectedD.lightweightE.challengeF.generatedG.journalH.eventuallyI.accurateJ.raisedK.criticallyThePowerofVBirdsofafeath

　　A.positioned B.resolution C.suspected D.lightweight E.challenge

　　F.generated G.journal H.eventually I.accurate J.raised K.critically

　　ThePowerofV

　　BirdsofafeathermayflocktogetherbutwhytheyflytogetherinVformationshasneverbeenknownforcertain.

　　Nowwiththehelpof14northernbaldibises(欧洲秃鹰)equippedwith__41__sensorsona600-milemigrationfromAustriatoItalyresearchersaresuggestingthattheexplanationisonethatwaslong__42__butneverproved:theformationshelpsthebirdsconserveenergy.

　　Reportinginthe__43__Naturethescientistswritethattheibises__44__themselvesinspotsthatwereaerodynamicallyoptimal(空气动力学上最佳的)–allowingthemtotakeadvantageofswirlsofupward-movingair__45__bythewingsofthebirdahead.Sincetheleadbirdgotnoliftadvantagetheibisesregularlyswitchedleaders.

　　“We’vebeenwonderingforyearswhetherflappingbirdscansaveenergybyfollowingeachotherintherightwas”saidGeiffreySpeddingaresearcherattheUniversityofSouthernCaliforniawhowasnotinvolvedinthestudy.“Thiswordanswersthatquestionandtheanswerisyes.”

　　ThescientistsledbyJimUsherwoodoftheRoyalVeterinaryCollegeinEnglandsaidamajor__46__wasobtainingthedata.TheibiseshatchedatZooViennainMarch2011and__47__aspartofaconservationprojectaimedatreintroducingthe__48__endangeredspeciestoitsnaturalrangeinEurope.

　　Someofthestudy’sauthorsservedashumanfosterparentstakingtheyoungbirdsontrainingflightsinSalzburgAustria.Thehumansrodeinaparaplaneatypeoflightweightaircraftandthebirdsfollowed.Eventuallythefosterparentstaughtthebirdstheir600-milemigrationroutefromSalzburgtoOrbetelloItalybyflyingalongsidethem.

　　Thebirdsworecustom-madedataloggersthatallowedtheresearcherstotrackflappingspeedanddirection.WeighinglessthananouncethedevicesincludedamemorycardandaGPSunitamongotherthings.Itis__49__toaboutonefootandrefreshesfivetimespers