Added the component minecraft:behaviour.random_fly as shown below does not have any effect on the entity. A parrot also has the same issue; it only follows its minecraft:behaviour.follow_mob behaviour component, thus sits stationary when no mobs are nearby.

        "minecraft:behavior.random_fly": {
          "xz_dist": 15,
          "y_dist": 1,
          "can_land_on_trees": false
        }