This is an Eastern Comma, Polygonia comma, one of the anglewing butterflies. It gets its name from a small, silvered mark on the ventral surface of its hind wing. Unfortunately, this particular butterfly refused to fold its wings sufficiently for me to get a shot of the comma.
One seldom sees one of these butterflies nectaring. They prefer other fare...tree sap, rotten fruit, scat, and carrion, for example. They overwinters as adults so it is not unusual to see this species out and about on warm winter days.