@ansosh92 It's a pun on two levels.
@Makinami is right that September is the 9th month, but also, sept- is a prefix meaning "seven," thus the title
With that naming sense, I wonder what he calls his birds. Actually, I'm pretty sure they've already been mentioned, but I can't remember. I don't know how I would have forgotten something that's like "Septimus" but you know, actually I would