迁徙动物Likemanyotheranimals,swallowswillflysouthwhenthedaysturncoldandtheleavesfromtreesbegintofall.Theytravelmanymilestofindawarmerwinter.Thistypeoftraveliscalledmigration(迁徙).Birdsareanimalsthatliketomigratealotwhenitiscold.About600outof9,000kindsofbirdsdoit.Theyleaveinautumnandcomebackduringthewarmspringmonths.Manybirdsdon’tlikethecold.Theyneedfood,butplantsdieandinsects(昆虫)hideinwinter.So,they’llonlycomehomethenextyear,whentherewillbeplentyoffoodforthemtoeat.Butthetripisoftenhardandnotsafe.Manybirdsflyingroupsandmakenoises.Cranes(鹤)flyingroupsliketheletterV,orinarow.Otherstravelinpairsoralone.Somecantravelaverylongway.Theyflybetweenlands.Forexample,theArctictern(北极燕鸥)cantravel20,100kilometers.TheybuildahomeneartheNorthPole(北极),gototheAntarctic(南极洲)inautumn,andthencomebackinspring.Howdothebirdsfindtheirway?Theylookatthingslikethesun,moonandstars.Theynevergetlost.阅读短文，根据短文内容填表（每空不超过三个单词,最后一空为开放性试题，可多于三个单词）Whatismigration?It’swhenanimalstravelfromcoldplacestofinda1winter.Theyleavein2andcomebackin3.Whydobirdsmigrate?Becauseplants4andanimals5.There’snotmuch6forthemduringcoldwinters.Howdobirdsmigrate?Thetripisoften7anddangerous.Manytravelin8and9.Howdobirdsfindtheirway?Theyfindtheirwaybylookingatthe10,11and12.Whatcanwelearnfrombirds’migration?Animalsarebornnaturallytobeableto13.