Why do birds fly in a 'V' formation?

 The birds fly in 'V' formation in order to achieve two purpose. One is the conservation of energy,because during their flight each bird flaps its wing,which creates an uplift for the following bird .The bird keep on taking turns from front to back when they get tried. Thus, they can over long distance without stopping for rest. Secondly
  flaying in V formation helps the flock of birds to communicate and coordinate within the groups, thus helping to keep the track of each bird.