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OurVanishingNightMostcityskieshavebecomevirtuallyemptyofstars.Ifhumansweretrulyathomeunderthelightofthemoonandstars,wewouldgoindarknesshappily,themidnightworldasvisibletousasitistothevastnumberofnocturnalspeciesonthisplanet.Instead,wearediurnalcreatures,witheyesadaptedtolivinginthesun'slight.Thisisabasicevolutionaryfact,eventhoughmostofusdon'tthinkofourselvesasdiurnalbeingsanymorethanwethinkofourselvesasprimatesormammalsorEarthlings.Yetit'stheonlywaytoexplainwhatwe'vedonetothenight:We'veengineeredittoreceiveusbyfillingitwithlight.Thiskindofengineeringisnodifferentthandammingariver.Itsbenefitscomewithconsequences—calledlightpollution—whoseeffectsscientistsareonlynowbeginningtostudy.Lightpollutionislargelytheresultofbadlightingdesign,whichallowsartificiallighttoshineoutwardandupwardintothesky,whereit'snotwanted,insteadoffocusingitdownward,whereitis.Ill-designedlightingwashesoutthedarknessofnightandradicallyaltersthelightlevels—andlightrhythms—towhichmanyformsoflife,includingourselves,haveadapted.Whereverhumanlightspillsintothenaturalworld,someaspectoflife—migration,reproduction,feeding—isaffected.Formostofhumanhistory,thephraselightpollutionwouldhavemadenosense.ImaginewalkingtowardLondononamoonlitnightaround1800,whenitwasEarth'smostpopulouscity.Nearlyamillionpeoplelivedthere,makingdo,astheyalwayshad,withcandlesandrushlightsandtorchesandlanterns.Onlyafewhouseswerelitbygas,andtherewouldbenopublicgaslightsinthestreetsorsquaresforanothersevenyears.Fromafewmilesaway,youwouldhavebeenaslikelytosmellLondonastoseeitsdimcollectiveglow.Nowmostofhumanitylivesunderintersectingdomesofreflected,refractedlight,ofscatteringraysfromoverlitcitiesandsuburbs,fromlight-floodedhighwaysandfactories.NearlyallofnighttimeEuropeisanebulaoflight,asismostoftheUnitedStatesandallofJapan.InthesouthAtlantictheglowfromasinglefishingfleet—squidfishermenluringtheirpreywithmetalhalidelamps—canbeseenfromspace,burningbrighter,infact,thanBuenosAiresorRiodeJaneiro.Inmostcitiestheskylooksasthoughithasbeenemptiedofstars,leavingbehindavacanthazethatmirrorsourfearofthedarkandresemblestheurbanglowofdystopiansciencefiction.We'vegrownsousedtothispervasiveorangehazethattheoriginalgloryofanunlitnight—darkenoughfortheplanetVenustothrowshadowsonEarth—iswhollybeyondourexperience,beyondmemoryalmost.Andyetabovethecity'spaleceilingliestherestoftheuniverse,utterlyundiminishedbythelightwewaste—abrightshoalofstarsandplanetsandgalaxies,shininginseeminglyinfinitedarkness.We'velitupthenightasifitwereanunoccupiedcountry,whennothingcouldbefurtherfromthetruth.Amongmammalsalone,thenumberofnocturnalspeciesisastonishing.Lightisapowerfulbiologicalforce,andonmanyspeciesitactsasamagnet,aprocessbeingstudiedbyresearcherssuchasTravisLongcoreandCatherineRich,co-foundersoftheLosAngeles-basedUrbanWildlandsGroup.Theeffectissopowerfulthatscientistsspeakofsongbirdsandseabirdsbeingcapturedbysearchlightsonlandorbythelightfromgasflaresonmarineoilplatforms,circlingandcirclinginthethousandsuntiltheydrop.Migratingatnight,birdsareapttocollidewithbrightlylittallbuildings;immaturebirdsontheirfirstjourneysufferdisproportionately.Insects,ofcourse,clusteraroundstreetlights,andfeedingatthoseinsectclustersisnowingrainedinthelivesofmanybatspecies.InsomeSwissvalleystheEuropeanlesserhorseshoebatbegantovanishafterstreetlightswereinstalled,perhapsbecausethosevalleysweresuddenlyfilledwithlight-feedingpipistrellebats.Othernocturnalmammals—includingdesertrodents,fruitbats,opossums,andbadgers—foragemorecautiouslyunderthepermanentfullmoonoflightpollutionbecausethey'vebecomeeasiertargetsforpredators.Somebirds—blackbirdsandnightingales,amongothers—singatunnaturalhoursinthepresenceofartificiallight.Scientistshavedeterminedthatlongartificialdays—andartificiallyshortnights—induceearlybreedinginawiderangeofbirds.Andbecausealongerdayallowsforlongerfeeding,itcanalsoaffectmigrationschedules.OnepopulationofBewick'sswanswinteringinEnglandputonfatmorerapidlythanusual,primingthemtobegintheirSiberianmigrationearly.Theproblem,ofcourse,isthatmigration,likemostotheraspectsofbirdbehavior,isapreciselytimedbiologicalbehavior.Leavingearlymaymeanarrivingtoosoonfornestingconditionstoberight.Nestingseaturtles,whichshowanaturalpredispositionfordarkbeaches,findfewerandfewerofthemtoneston.Theirhatchlings,whichgravitatetowardthebrighter,morereflectiveseahorizon,findthemselvesconfusedbyartificiallightingbehindthebeach.InFloridaalone,hatchlinglossesnumberinthehundredsofthousandseveryyear.Frogsandtoadslivingnearbrightlylithighwayssuffernocturnallightlevelsthatareasmuchasamilliontimesbrighterthannormal,throwingnearlyeveryaspectoftheirbehavioroutofjoint,includingtheirnighttimebreedingchoruses.Itwasoncethoughtthatlightpollutiononlyaffectedastronomers,whoneedtoseethenightskyinallitsgloriousclarity.And,infact,someoftheearliestciviceffortstocontrollightpollution—inFlagstaff,Arizona,halfacenturyago—weremadetoprotecttheviewfromLowellObservatory,whichsitshighabovethatcity.Flagstaffhastighteneditsregulationssincethen,andin2001itwasdeclaredthefirstInter