Zapdos can go wild once you deliver the Ruby and Sapphire to the islands. Back when the game was released in 2012, we had a Zapdos at the end of the Power Plant, then they removed it, it should come out in there but no, you can only get it on the grass and in the water using Surf. Outside the caves and during the month that that bird comes out (in this month you can find Zapdos), the next month it will be Moltres and the next Articuno, thus in an endless cycle for now.