One of the Grey Wagtails, not seen for some time, had returned to the little pool at the top of the Dell, above the bridge where they nested.
Its grey back and yellow front blend harmoniously into the background of lichen-covered rock. Having a light-coloured underside makes it harder to see the shape of the bird from a distance; this is known as 'counter-colouring'. Its relative the Pied Wagtail uses 'disruptive colouring', a strong black and white pattern to break up its outline, like the dazzle-painted ships of the First World War -- here is an example.
The pigeon-eating Lesser Black-Backed Gull was trying to sneak up on a bunch of them on the roof of the Dell restaurant. The surviving pigeons are now well aware of its intention, and panicked.
They are faster off the mark than a big gull, and it didn't get near one. But it seems to be doing all right, judging by the number of clean-picked pigeon carcases seen on the shore of the Serpentine.
The young blonde Egyptian Goose, not seen on the Serpentine for a while, has turned up beside the Round Pond.
Probably she was driven off the lake by the triathlon, which has just ground interminably into its last day.
Here is a Great Crested Grebe taking off from the Long Water. In still air it needs a 50-yard run, propelled by its powerful feet, to reach unstick speed. This can be reduced by heading into the wind to develop more lift in its smallish wings.
And this grebe is in the typical low posture that grebes adopt when bringing fish to their young when there are gulls around waiting the snatch a meal. They dive frequently on the journey to put marauders off the trail.
Joseph reports what may have been the last sighting this year of our Hobby family, on Thursday. They were seen on St Matthew's church in St Petersburgh Place, a couple of hundred yards from the northwest corner of the park. There were two parents and three young -- we hadn't suspected that there were more than two when they were in the park. They were calling excitedly. This street has a synagogue with two tall towers and a neo-Gothic church with a spire and lots of ornamental projections, and at the far end the Greek Orthodox cathedral with a big dome, so it offers plenty of perches to birds of prey.