Your junco thinks he's attacking a rival for his territory and or mate. Why
he's cued into attacking only the right side is anybody's guess. Most cars
aren't exactly symmetrical and since he's had a problem with his "rival" on
the right side that's the area he thinks his territory is most vulnerable.
We had a similar problem with a Song Sparrow and a pickup mirror for 4
years. Just keep the mirrors covered for a few weeks. Robins are notorious
territory defenders too.
Steve Ellis
Coupeville, Wa
sellis at coup.wednet.edu