When using a parrot monster spawner using commands, for example:

/setblock ~ ~ ~ minecraft:spawner{Delay:0s,MaxNearbyEntities:5s,MaxSpawnDelay:20s,MinSpawnDelay:10s,RequiredPlayerRange:15s,SpawnCount:5s,SpawnData:

,SpawnPotentials:[{Entity:

,Weight:1}],SpawnRange:4s}

it will spawn parrots mid air. However when the air is cave_air, it will not spawn any parrots.

Note: When using the fill command to place cave_air, make sure to place another block, e.g. stone. Replacing air with cave_air seems to fail.