▁or ▁used ▁to ▁eng age , ▁in ▁mass ▁migr ations . ▁Of ▁these ▁migr ations , ▁those ▁of ▁the ▁spring b ok , ▁black ▁w ilde be est , ▁b les b ok , ▁sc im itar - horn ed ▁or y x , ▁and ▁k ul an ▁have ▁ceased . ▁Long - distance ▁migr ations ▁occur ▁in ▁some ▁b ats , ▁not ably ▁the ▁mass ▁migration ▁of ▁the ▁Mexican ▁free - ta iled ▁bat ▁between ▁Oregon ▁and ▁southern ▁Mexico . ▁M igration ▁is ▁important ▁in ▁cet ace ans , ▁including ▁wh ales , ▁dol ph ins ▁and ▁por po ises . ▁ ▁In ▁other ▁animals ▁ ▁Some ▁re pt iles ▁and ▁am ph ib ians ▁migr ate . ▁Some ▁cr ust ace ans ▁migr ate , ▁most ▁spect ac ular ly ▁the ▁Christmas ▁Island ▁red ▁c rab ▁which ▁moves ▁en ▁mas se ▁each ▁year ▁by ▁the ▁million . ▁ ▁Track ing ▁migration ▁ ▁Scient ists ▁gather ▁observations ▁of ▁animal ▁migration ▁by ▁tracking ▁their ▁movements . ▁Anim als ▁were ▁tradition ally ▁track ed ▁with ▁identification ▁tags ▁such ▁as ▁bird ▁rings ▁for ▁later ▁recovery ; ▁no ▁information ▁was ▁obtained ▁about ▁the ▁actual ▁route ▁followed ▁between ▁release ▁and ▁recovery , ▁and ▁only ▁a ▁small ▁fraction ▁of ▁tag ged ▁individuals ▁were ▁generally ▁recovered . ▁More ▁convenient , ▁therefore , ▁are ▁electronic ▁devices ▁such ▁as ▁radio ▁tracking ▁coll ars ▁which ▁can ▁be ▁followed ▁by ▁radio , ▁whether ▁hand h eld , ▁in ▁a ▁vehicle ▁or ▁aircraft , ▁or ▁by ▁satellite . ▁Tags ▁can ▁include ▁a ▁G PS