The male Little Owl in the sweet chestnut tree took exception at being stared at, and flew round the tree. We went to the other side, but there was no sign of him, and there didn't seem to be a hole nearby that he could have gone into. After some time it became clear that he had flown right away from the tree in a straight line that prevented us from seeing him. I had seen him do this same trick a few days before when he was being pestered by a Magpie. Neither I nor the Magpie had any idea where he had gone.
A kind person showed me the Green Woodpecker's nest I had been searching for yesterday, though nothing was going on there. It's where the path from the Albert Memorial to the Physical Energy statue crosses the path that runs from just south of the Serpentine Gallery to loop around the north of the Round Pond. The tree is a tall plane on the northeast corner of the intersection, and the hole is on the south side under the stump of a branch, about 30 ft up and easily visible from the path. It is perfectly round and looks as if it had been cut with a power tool. Coordinates are 51.5054,-0.177922 .
A very bold male Chaffinch who is now coming to my hand to be fed has pursued me over an area stretching from the Round Pond to the Italian Garden, a large range. Anywhere in this area, there is a sudden loud chirp and there he is, sitting on a twig expecting to be given a pine nut.