migration

migration
    n 1: the movement of persons from one country or locality to
         another
    2: a group of people migrating together (especially in some
       given time period)
    3: (chemistry) the nonrandom movement of an atom or radical from
       one place to another within a molecule
    4: the periodic passage of groups of animals (especially birds
       or fishes) from one region to another for feeding or breeding
    

Migration \Mi*gra"tion\, n. [L. migratio: cf. F. migration.]
   The act of migrating.
   [1913 Webster]
    

57 Moby Thesaurus words for "migration":
      communication, conduction, contagion, convection, delivery,
      deportation, diapedesis, diffusion, dissemination, emigration,
      expatriation, export, exportation, expulsion, extradition, flight,
      immigration, import, importation, in-migration, interchange,
      intermigration, metastasis, metathesis, metempsychosis,
      mutual transfer, osmosis, out-migration, passage, passing over,
      perfusion, remigration, run, spread, spreading, swarm, swarming,
      transduction, transfer, transfer of property, transference,
      transfusion, transit, transition, translation, translocation,
      transmigration, transmigration of souls, transmission, transmittal,
      transmittance, transplacement, transplantation, transposal,
      transposition, travel, trek