Who’s · Salmon and steelhead trout perform amazing annual feats of navigation ... the...
Transcript of Who’s · Salmon and steelhead trout perform amazing annual feats of navigation ... the...
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How can timber wolves travel across hundreds of miles of forests, swamps, lakes, and rivers without getting lost?
How can steelhead trout navigate the big waters of Lake Superior and find the North Shore stream where they hatched as baby trout?
How can hummingbirds make incredibly long and dangerous journeys for migration every spring and fall?
W ithoutmaps,compasses,orothernavigationaltools,Minnesotawildanimalstravelhundredsoreven
thousandsofmiles.Toguidetheirway,theymightreadweatherandsunlight.Theymightfollowrivers,mountainranges,orotherlandmarks.Inaddition,theymightrelyonspecialadaptations(bodychangesthatevolvedovertimetohelpthemlivebetterintheirenvironment)andinstincts(automaticresponsesthatarenatural,notlearned).
By Tom Anderson
Who’s That
Navigator?
September–October2007 35Gray wolf by stan tekiela; steelhead trout by scott ripley, windiGo imaGes; ruby-throated humminGbird by michael furtman
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Champion NavigatorsBirdsarechampionnavigators.Manyspeciestravelacrossentirecontinents.Forexample,bobolinks,Baltimoreorioles,andruby-throatedhummingbirdsareNeotropicalmigrantsthatwinterinthetropicsandmigratetoNorthAmericatonestinspring.Thesebirdsmakethisjourneybecausetheirfavoriteandnecessaryfoodsbecomescarceorunavailableasseasonschange.Forexample,ruby-throatedhummingbirdsdependonnectarfromflowers.WhenflowersstopbloominginMinnesota,theyflysouth.SomeflyalongtheMexicancoast.OthersflyacrosstheGulfofMexico—upto20hoursnonstop—toCostaRica,Nicaragua,andothercountriesinCentralAmerica.
Dangerous FlightsManyofthemillionsofbirdsthatmigrateeachyeardieduringtheirmigration.Theirjourneyssometimestakethemthroughstrongwinds,heavyrains,thunder,lightning,andevensnowstorms.Theymightencountervariouspredators,fromhawkstohousecats.Tallbuildingsandwiresfromradioandtelevisiontowerscanbedeadlyforbirdsthatnavigateatnight.
A male ruby-throated hummingbird sips nectar.
Forhundredsofyears,ornithologistsandnaturalistshavebeeninvestigatingthemysteriesofbirdmigration.Theyhavelearnedthatbirdsuselandmarkssuchascoastlines,rivers,mountainranges,andothergeographicalfeaturestosteeracourse.Formanybirds,thesunanditspositionintheskyaidnavigation.Birdsthatmigrateatnightsteerbythestarsandplanets.ScientistshavelongtheorizedthatbirdsuseEarth’smagneticfieldtohelpthemmigrate,buttheydon’tknowexactlyhow.Someevidencesuggests
Ace Pilots
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thatmicroscopicparticlesofironintheupperbeakofsomebirdspeciesactlikeamagneticcompassneedle.Otherstudiesshowthebird’sinternalcompassismorecomplicated,workingthroughchemicalreactionsatthemolecularlevel.
Migration Routes
Bobolink
Ruby-throated Hummingbird
Argentina
Costa Rica
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SalmonandsteelheadtroutperformamazingannualfeatsofnavigationbetweenLakeSuperioranditstributarystreams.
Steelhead,amigratoryformofrainbowtrout,hatchupstreamfromthelakeintheshallow,gravelyareasofmanyriversinMinnesota,Wisconsin,Michigan,andCanada.Aftertwoyearsinmoststreams,theyoungfish(calledsmolts) thenmigrateintoLakeSuperioranddisperse.
Afterlivingandgrowinginthelakeforaboutthreeyears,thesteelheadreturntotheirhomestreamstospawn.StandingatthemouthofaNorthShorestreaminspring,youmightbeluckyenoughtospotseveraloftheselargefishintheshallows.Alittlefartherupstream,youmightseeasteelheadleapupasmallwaterfall.
Water PilotsTonavigatetothestreamswheretheyhatched,migratoryfishuse
avarietyofhomingmechanisms.Somefishusethepositionofthesuntofindtheshorewiththemouthoftheirhomestream.Fishinthesalmonfamilycontainmicroscopicparticlesofironintheirbrain.Theironactslikethemagneticneedleinacompass,enablingthesalmontoorientitselfbyadjustingtoEarth’smagneticfield.
Asenseofsmellhelpssomefishsniffouthome.Whatsmellsfromyourchildhoodwillyoualwaysremember?Steelheadandsalmonrememberthesmellofthestreamwheretheylivedasyoungfish.
Eachstreamhasasignatureofsmellsinitswaterchemistry.It’sacollectionofblendedchemicalsfromthesurroundingland,likeacidsfromdecayingleavesinthestream.Justasyoumightfollowyournosefromonepartofyourhousetowardatemptingaromacomingfromthekitchen,anadultfishsmellsitswayfromthelaketothestream.
Migratory Fish
Steelhead trout, a type
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Duluth French River
Knife River
Gooseberry River
Baptism River
Temperance River
Brule River
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ThelargestmemberofthewilddogfamilyinMinnesotaisthegraywolf,ortimberwolf.Wolvesliveinpacksanddonotmigrate,buttheirhometerritoriessometimescoverhundredsofsquaremiles.Justasyoulearnyourwayaroundyourneighborhood,wolveslearnhowtogetaroundtheirvasthomegroundtofindfoodandshelter.
WolvesinMinnesotafollowmooseorwhite-taileddeertohuntthem.Thenthewolvessomehowfindtheirwaybackhome.Theyreturnhomebyinstinct,orbya
senseofhomethatispartofthebrainandnervoussystem.
Good NosesWolvesdependontheirsenseofsmelltofindtheboundariesoftheirlargehomeranges.Likeyourpetdog,thewolfurinatestomarkitsscentonstumps,rocks,orshrubs.Otherwolvespassbyand“read”thesescentposts—theyfindoutwhoclaimstheterritory.Wolveshowltocommunicatewithinapack.Ifawolfgetsseparatedfromitspack,howlingcanhelpitreunitewiththepackanditshometerritory.
Wolf Ways
A gray wolf crosses the Kettle River near Sandstone.
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Wolf range
A few wolf territories as mapped by DNR wolf biologists.
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Imagineyouare,likeawolf,travelingandtryingtofindyourwaybacktoyourhometerritory.Youknowthatyoumusttravelnorth,butyouhavenocompass.Hereareafewnaturaltricksforfindingnorth,south,east,andwestinthewild.
Find Your Direction
1FindtheNorthStaronaclearnight.FirstfindtheBigDipper,thedipper-shapedgroupofstarsintheconstellationUrsaMajor.Thenfindthetwostarsontheoutsideofthedipper’scup.ImaginealineconnectingthosetwostarsandfollowituptothebrightstarknownastheNorthStar,orPolaris,whichalwaysappearsinthenorth.
2Lookformossgrowinghighonthetrees.Mosspreferstogrowwheremoisturelingers,soittendstogrowhighestonthenorthsideofthetrunkwhereitisshadedfromthesun.
3 Compareplantsonasouth-facinghillsidetoplantsonanorth-facinghill.Southernslopeswithconstantexposuretothehot,dryingsunhavefardifferentvegetation.
4Notethepositionofthesunonaclearday.Itrisesintheeast
andsetsinthewest.InwinterinMinnesota,thesunstaysinthesouthernskythroughouttheday.
5 Studyathatch-buildingantmoundinsummer. Totakeadvantageofthesun’swarmth,red-and-blackthatchantsusuallyworkmoreonthesouthsideoftheirmound.Theykeepthissidefreeofvegetation.Becauseitreceivesmoreanttraffic,thesouthsidealsoslopesmorethanthenorthsidedoes. nV
Special offer to teacherS
Sign up for free classroom subscriptions to Minnesota Conservation Volunteer. Thanks to a generous gift from Dale L. Charbonneau, Minnesota teachers and students may subscribe free for the 2007–2008 school year. Go to www.mndnr.gov/young_naturalists.
Also online, find free teachers guides to this and other Young Naturalists stories.
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North Star
Little Dipper
Big Dipper