After a while I saw a bird of prey, which looked very much like an eagle, flying low to the ground. It was quite far off so I did not manage a positive ID. Now it all made sense. The juvenile was being told to remain out of sight by the parents.
After a while the female bird flew back from her outpost to a clump of rocks closer to the burrow and perched there. Sure enough a few minutes later out popped the juvenile and joined Mum on the rocks for a bit of bonding.