I've just discovered a wrens nest in a tree outside our patio. Tiny Mum and Dad are flitting backwards and forwards feeding the babies who are in a hole in the tree trunk. I can hear them making a very high pitched call as soon as the parents get near to the tree. The babies have been out of the nest, but are back in now waiting for more food.
One of the parents, with a beak sticking out of the hole in the tree