—Birchstar to the SkyClan cats after a tree landed on them Code of the Clans, page 21
Birchstar is an ancient SkyClanleader. When Duststar, leader of WindClan asks if every Clan had made it to Fourtrees, Birchstar springs up onto the rock beside the WindClan leader, confirming that every Clan is there. As the first rule of the warrior code is being discussed, Birchstar nods along with Hollystar of ShadowClan. When Hollystar asks the other leaders how they would have less contact across borders, but let the other Clans know of dangers around the territories. Birchstar responds to this, suggesting a meeting at Fourtrees every full moon to gather in peace and share news. Duststar agrees to this, and Birchstar answers that that is all she asks.
Shortly after Brindlestar, the new leader of ShadowClan, begins the Gathering with an accusation against Whitestar and ThunderClan, Birchstar points out that each Clan lives in a place where they are best suited for hunting. Quickly after a huge branch from a giant oak snaps and falls onto the gathered cats, Birchstar dashes to the edge of the Great Rock and peers down, asking if the SkyClan cats are all right. She calls out to them once more, asking if the SkyClan cats can hear her speak. Her deputy, Rainsplash, calls out that all of them are fine.
After it is found that no cat from any of the Clans is injured, Birchstar and the other Clan leaders decide to make a new law in the warrior code that says that borders between territories should not be crossed. It is backed up as they believe StarClan sent the branch as a sign, which means that the Clans should be split apart. As the branch fell, it split the cats apart from each other and into their own separate Clans, similar to boundaries.