I've had this nest on for much of the day and am completely fascinated by Joplin's behaviour! I've been away for awhile and see that Heather is still on the nest and the folks on the chat point out that she hatched a day after Joplin, so she might not fledge until tomorrow. They're very similar, obviously, but according to the "chatters", Heather has a shorter tail and a thicker neck. Sometimes when the two of them are together, I can see a bit of difference between them, but it's very difficult!