Red signal
The area can be expanded by contracting a muscle behind the area. This stretches the elastic skin of the area.
Neck muscle
The contracted muscle can be seen as a raised bump on the neck behind the red spot.
Signal's function
The significance of the red spot is not known, but it is clearly some kind of signal between the male and female. Its colour also becomes deeper during the well-known dance of the cranes, and when they copulate.
Display's function
The exact role of the joint display is not understood, either. Possibly, its function is to strengthen the pair bond.
