How do you get Zapdos in Pokemon Mystery Dungeon?

To recruit Zapdos, first, you need to recruit Articuno and Moltres. Afterwards, Articuno and Moltres will tell you to go to Sky-Craggy Isle to look for Zapdos.

Upon arriving at Sky-Craggy Isle, you will see some clouds looming in the sky, and you will be prompted to investigate them. Upon flying up to the clouds, you will be ambushed by Zapdos. Defeat it, and you will be given the option of inviting Zapdos to your team.