When the hemp birds press their mouths, they should listen and learn often. To choose mixed audio, that is, the audio contains both the call of the mackerel and the original call. Let it listen more and learn more, and it will be easy to get the sound you want.
Note that the volume is slightly louder than the bird's cry, but it is appropriate not to affect the bird's cry. The time cannot be too long. It is best not to use it during the rest of the time when the chicks are crowing and shedding their feathers.