a quote attributed to maya angelou on her commemorative stamp released by the us postal service is actually that of another writer .
` a bird does n't sing because it has an answer , it sings because it has a song , ' reads the stamp , a quote that has long been attributed to angelou .
joan walsh anglund wrote the words in her 1967 book a cup of sun .
angelou , the acclaimed author of such classics as i know why the cage bird sings , was issued the forever stamp for her contributions to the arts .
the stamp was unveiled tuesday at an event featuring first lady michelle obama , oprah winfrey and postmaster general megan j. brennan .