Couples.
I always find it fascinating to see the differences in the appearance of birds. Here is a little selection.
(top two rows: Rose-breasted Grosbeak, Red-bellied Woodpecker, Northern Cardinal, Red-winged Blackbird - ladies in row 1, gents in row 2
third row: Mourning Doves and House Finches, they wanted to be in the same photo with their partners :D)