/ˈheməsfɪə $ -fɪr/ (n.) one half of the Earth; also, one half of a sphere … migration of this type takes place primarily into the higher latitudes of the Northern _______ .

/ɪnˈdjʊə $ ɪnˈdʊr/ (v.) to live under difficult conditions … winter season in nearby valleys, enduring some of the coldest conditions on Earth.

/ɪmˈperətɪv/ (n.) a priority; an urgent need Migration is an excellent example of how nature has responded to the biological _______ for species to evolve and spread out

/briːd/ (v.) to reproduce Migration is the regular movement of animals between their _______ ing grounds and the areas that they inhabit during the rest of the year.

/ˈɒptəməl $ ˈɑːp-/ (Adj.) best, most favorable This form of migration allows birds to breed in areas that provide _______ conditions for nesting and feeding their young.