Same here. I've always heard that term -- so no need to be embarrassed. I think some migrate further south than the others and so their trip north takes them longer to get back here and they arrive later. I don't know why that is either. The males tend to migrate first (or so I've been told) and so start back north sooner and tend to arrive earlier. I have noticed that I see male ruby-throats here before I see the females. Perhaps that's just a coincidence.