Twice in the last week I have seen a female cardinal feed another one.  I believe she was feeding on sunflower seed.  This was unusual behavior.  The two were adult females.  And neither appeared to be hurt or injured in any way.  Once they were on the ground.  And another time on the bird feeder that had mostly sunflower seed on it.  One fed the other directly beak to beak.  This behavior had me stumped.