It's simple drafting. They are cutting down on wind resistance, when the lead goose gets tired he moves back. They can go further distances this way before resting.

You could probably google this and come up with the answer.

Also google the B1 canards, or Smucks (SP?). They are used only in Low Altitude high speed flight where they dampen the nose of the airplane thereby reducing crew fatigue. As opposed to an airplane like the Eurofighter or Rafale that uses them to increase angle of attack without loss of lift on the forward section of the fuse, thereby getting more agile, however, there is a loss of speed.

Everything in aviation is a compromise