Fill in the Blanks (Reading & Writing)

Each spring and autumn, vast numbers of birds undertake long migrations between breeding and wintering grounds, —coveringcoveredcovercoverage thousands of kilometres in only a few weeks. Some species navigate using the position of the sun and stars, while others appear to —sensesensitivesensiblesensation the Earth's magnetic field. Habitat loss along traditional stopover sites now —threatensthreatthreateningthreatened many migratory populations, since the birds depend on these areas to rest and refuel.