This is a Carolina chickadee, the closest bird that I have here to the family of birds called tits in the UK. And looking at pictures of the Marsh tit, it looks almost identical to the Carolina chickadee. In fact, tits, chickadees and titmice belong to the same family, Paridae. Type in "Chickadee" into Wikipedia and it automatically takes you to the listing for tit. Not quite a blue tit (which I long for), but the closest that I'll get here in North Carolina.