Parrots will not spawn in a 1.11 generated world with the current version of Spigot 1.12. Minecraft vanilla will spawn them but not with Spigot. The only way I can get them to spawn is to MCEdit a section out of a jungle and generate those deleted chunks in Spigot 1.12. Mojang had made it retroactive but it seems Spigot is holding that feature back.