As I was passing the Serpentine Gallery there was a furious rattling sound and two Carrion Crows erupted out of a tree, chased by a pair of Song Thrushes who were clearly building a nest. The thrushes then turned on a Green Woodpecker, which retreated around the back of the trunk.

But that was to no avail, and soon the woodpecker was routed as well. There is also a pair of Mistle Thrushes in a tree nearby, which attack Magpies furiously. The male is singing but there is no sign of a nest yet.

Later, when I was coming home along the south side of the Serpentine, the same thing happened again. Here is one of the thrushes shouting abuse at a couple of Magpies and four Carrion Crows, all of whom left the scene, if only in the hope of a bit of peace and quiet.

It is amazing how bold these normally timid birds become when there is a nest to defend. Both Song and Mistle Thrushes have been singing loudly in many parts of the park, and for the past two days a Blackbird has been singing from a tree north of the Flower Walk. Blackbirds start singing later than the other thrushes.

Two pairs of Starlings that nest in the plane trees on the edge of the Serpentine have started work on whatever it is that Starlings do to make their nests habitable -- you never know what this is, because you can't see into the hole.

A few years ago I tried to photograph the inside of a Starling's nest containing young in one of these trees, holding the camera at arms' length above my head and using flash to illuminate the inside of the hole. I got a clear shot of the inside of the hole, but no sign of a living creature. The nest was farther inside the hole, out of site round a corner.

When these nests are in operation, you often see a parent Starling fly out of the hole and straight as an arrow across the lake to the Lido restaurant to scavenge some food for the youngsters. It is less work that poking around in the nearby grass for wireworms.

Near the Serpentine island, a Great Crested Grebe was enjoying a wash.

In a week from now it will be time to start searching seriously for the Tawny Owls and their owlets. Last year they turned up late, in a completely unexpected place 200 yards from their nest tree. It is a challenge, but a lot of practised owl watchers will be searching, and as soon as anything is found it will be noted on this blog.