I returned to the nest site today but I wasn't able to see any birds around the nest burrow. They are obviously very mobile and there is no specific reason for them to be around the burrow now. I did hear the male at one point, it was very close to me but unfortunately it coincided with the arrival of two kayakers who disturbed it and off it went, calling as it flew down river. The picture is from the day they left the nest, 48 hours ago now.