In the U.S. Army, Air Force, and Marines, a Lieutenant Colonel has a silver oak leaf as his rank insignia.  A full Colonel has, as his insignia, an eagle with a shield.  The term “full-bird Colonel” refers to the eagle, which distinguishes the Colonel from the lesser Lieutenant Colonel, whose insignia does not include an eagle nor any other avian creature.

  Below are the insignia for a “full-bird Colonel” and a Lieutenant Colonel, respectively.