First I noticed a Song Sparrow sitting beside a recently fledged Cardinal (seems pretty late) for a while, then it was making some kind of feeding or pecking motion towards the Cardinal. Later another Song Sparrow joined and they were landing on the Cardinal's back and pulling its wing, and eventually the Cardinal moved a bit out of sight. Mama Cardinal was in the vicinity but didn't intervene, either she didn't notice or didn't care.
/Thomas