LETTERSVisualbutnottrigeminalmediationofmagneticcompassinformationinamigratorybirdManuelaZapka1,DominikHeyers1,ChristineM.Hein1,SvenjaEngels1,Nils-LasseSchneider1,Jo¨rgHans1,SimonWeiler1,DavidDreyer1,DmitryKishkinev1,J.MartinWild2&HenrikMouritsen1Magneticcompassinformationhasakeyroleinbirdorientation1–3,butthephysiologicalmechanismsenablingbirdstosensetheEarth’smagneticfieldremainoneoftheunresolvedmysteriesinbiology2,4.Twobiophysicalmechanismshavebecomeestablishedasthemostpromisingmagnetodetectioncandidates.Theiron-mineral-basedhypothesissuggeststhatmagneticinformationisdetectedbymagnetoreceptorsintheupperbeakandtransmittedthroughtheophthalmicbranchofthetrigeminalnervetothebrain5–10.Thelight-dependenthypothesissuggeststhatmagneticfielddirectionissensedbyradicalpair-formingphotopigmentsintheeyes11–15andthatthisvisualsignalisprocessedinclusterN,aspecialized,night-timeactive,light-processingforebrainregion16–19.HerewereportthatEuropeanrobinswithbilaterallesionsofclusterNareunabletoshoworientedmagnetic-compass-guidedbehaviourbutareabletoperformsuncompassandstarcompassorientationbehaviour.Incontrast,bilateralsectionoftheophthal-micbranchofthetrigeminalnerveinEuropeanrobinsdidnotinfluencethebirds’abilitytousetheirmagneticcompassfororienta-tion.ThesedatashowthatclusterNisrequiredformagneticcompassorientationinthisspeciesandindicatethatitmaybespecificallyinvolvedinprocessingofmagneticcompassinformation.Further-more,thedatastronglysuggestthatavision-mediatedmechanismunderliesthemagneticcompassinthismigratorysongbird,andthattheputativeiron-mineral-basedreceptorsintheupperbeakcon-nectedtothebrainbythetrigeminalnerve6–8areneithernecessarynorsufficientformagneticcompassorientationinEuropeanrobins.Thirty-sixEuropeanrobins(Erithacusrubecula)werecaughtwithin200mofthetestingsiteandtheirspontaneousmigratoryorientationwastestedinmodifiedEmlenfunnels20,2