The Great Crested Grebe family were at the southeast corner of the Serpentine island, invisible behind the wire baskets. But is was clear that they were there, because the father arrived carrying a small fish, swimming alternately above and under water to confuse any predator that might the following him, and dived under the basket to get to his family. These floating baskets sometimes break loose from their moorings and have to be towed back and refixed.

In another part of the lake, a grebe could be seen swimming under water, looking for food among the algae. In this picture the bird looks impossibly long and thin because of the refraction in the water -- though they are very slim and streamlined in reality.

After a while, the grebe swam along the shore to get to a better fishing ground, at an underwater cruising speed of 4 mph, so that I had to walk briskly to keep up. They exceed this speed when chasing fish, though I would not like to estimate how fast they can go.

Large wire baskets full of brushwood are being sunk in various places in the Serpentine. Earlier, bundles of the same kind of brushwood were put in the water all round the edge of the island. I spoke to one of the men doing it, and he said that the idea was that the twigs would be colonised by beneficial microorganisms that would clean the water. It can't do any harm.

While I was feeding some Coal Tits off my hand, a Goldcrest turned up and showed interest, though it didn't summon the courage to come down. It would be very pleasing to be able to attract these tiny birds. Even the Coal Tits only started coming to the hand this year. Now they are very bold, though they have to wait until the larger birds have had their turn.

While people were feeding the cygnets of one of the Mute Swans, a Carrion Crow tried to grab some of their food. The mother swan saw it off.

There was a Blue Tailed Damselfly among the wild plants near the bridge, mixing with the Common Blues that I illustrated earlier.

The Mistle Thrushes near the Serpentine Gallery have at least one young bird -- half grown but still dependent on its parents. It was sitting in a lime tree waiting to be fed. 

I heard one of the parents dive-bombing a Carrion Crow and went over to have a look. The intruder disposed of, the thrush was strolling around unconcernedly a few feet away from some picnickers. These shy birds are not bothered by people if they see that the people are quietly getting on with their own affairs and taking no notice of them. But before I could take a picture, a woman talking on her mobile, blind and deaf to the world, blundered on to the scene and frightened it away. It flew into the lime tree, so I went to have a look, and found the young thrush.

Some of the Greylag Geese on the Serpentine have almost completed the growing of their new primary feathers.

Three cygnets, younger than those in the Lido Mute Swans' first brood of seven, have just grown large enough to drive off Coots without help from their parents. Someone was feeding them on the edge of the Serpentine, and they clearly enjoyed seeing off the intruders and grabbing the food for themselves.

There is a family of Goldcrests in a cedar tree at the southeast corner of the Dell. They were loudly audible but wouldn't come out of the shadows to be photographed, and why should they?

There is another brood of Red Crested Pochards on the Long Water, the second this year. Only small numbers of these birds breed in this country, and the London parks are among the most prolific breeding sites. Sadly, when I photographed them one of the ducklings was in the last few seconds of its life, as it was seized by one of the gang of three Lesser Black-Backed Gulls, borne away and swallowed at a single gulp.

Surprisingly, the two broods of six and four Mallard ducklings were still intact. Their mothers are keeping them well under the bushes, perhaps having learnt from bitter experience what happens when you go out into the middle of the lake.

A Blackbird in the leaf yard had added some fine imitations of Nuthatch and Chaffinch song to his repertoire. Not far away, another Blackbird was doing Song Thrush impressions. The imitations come in the second half of each phrase, after a purely Blackbird opening -- but even the opening is different every time, as these inventive musicians never repeat themselves.

The Reed Warbler at the bottom end of the Serpentine was still singing, in exactly the same place as yesterday. I didn't hear the Reed Warbler in the reeds near the bridge, but there was a pair of Common Blue Damselflies mating. The male is the blue one on the left.

There are more and more Wood Pigeons in the park. Elizabeth saw a flock of 50 a few days ago.

As I was coming home past the Round Pond, I saw some people feeding the birds on the edge of the water: a few of the pond's 60-odd Mute Swans, a Canada Goose, about 200 Starlings and the inevitable pigeons. Then three young thugs turned up and started running at the birds and trying to kick them. Amazingly, at this moment a police van raced up and two policemen leapt out and seized them, actually putting them in handcuffs, and within half a minute another car turned up with two policewomen. I watched this spectacle with a certain vengeful enjoyment.

Today I did the monthly bird count around the Long Water and Serpentine, made difficult by much of the shore being occupied by the Olympic construction site. The number of geese currently on the lake moulting their wing feathers was 333, composed of 282 Greylags and 151 Canadas. Some Canadas have left in the past fortnight.

There was a Grey Heron in the abandoned nest at the east end of the Serpentine island. I think it was just using it as a convenient perch and did not intend to return to it seriously, as it left soon afterwards and stood on a wire mesh plant box instead, staring at the new Great Crested Grebe family who were safely out of reach.

Another heron stood in the Dell, eyeing the large carp in the water. The fish are far too big for it to catch, but herons are always hopeful.

The Coot family under the ledge of the Dell restaurant were out and about. Here one of the parents dives with the usual clumsy splash to bring up some algae for the chicks. They are very buoyant birds and find it hard to stay submerged. As soon as they stop swimming downwards they pop up like corks.

There are two new broods of Mallard ducklings on the Long Water, one of six and the other of four. There was one Lesser Black-Backed Gull in sight, and both mother ducks were keeping their offspring close to the edge, ready to retreat to cover if the gull came nearer.

A Reed Warbler was singing loud and long in the reeds on the southeast corner of the Serpentine. Let's hope that some of them manage to breed before it's time for them to migrate back to Africa.

The Great Crested Grebes nesting on the Serpentine island have taken their chicks out of the nest, and they were being carried on their mother's back. Prudently, she had kept behind the wire baskets that surround the island, and it was impossible to count the chicks, let alone take a photograph. Their father, just relieved from his carrying duties, was out in the lake washing off the mess and getting himself comfortable before he went fishing.

He managed to catch several very small fish, which is encouraging both for grebes and for people worried about the state of the lake.

On the other side of the lake, an Egyptian Goose was also having a bath.

The Coots nesting on a bottle crate under the sill of the Dell restaurant have four chicks. Although there were several Lesser Black-Backed Gulls cruising around hopefully, the overhanging concrete ledge was enough to keep them safe. A gull would have to fly over a Coot's nest to snatch a chick; if it went in on the surface the angry parents would see it off.

Often when I walk past the Serpentine Gallery, I see a large female Sparrowhawk heading southwest; she seems to have a daily routine. Today her travel plan was disrupted when a couple of Crows went up and chased her, shouting hoarse insults. She left in a hurry.

One of the Reed Warblers was singing in the patch of reeds on the Long Water by the bridge. Nearby, the Moorhens that nest in the drain have one chick. There are probably more on the way, as one of the adults went into the drain and did not emerge for some time.

The Great Crested Grebes nesting on the island are still in good order. Here is a photograph, too distant but the best I could do, of the two chicks seen so far looking out under their father's left wing. Their mother was out in the lake fishing busily but not catching much. There are now some young fish up to 2 inches long in the lake. It will be easier for the grebes when their young are a little larger and can be taken to the meal instead of having to carry the catch several hundred yards back to the nest.

A Song Thrush was singing gloriously from a dead branch near the Henry Moore sculpture. There is only about a week to go before they fall silent till next spring. Both Blackbird and Song Thrushes develop their songs over the season, so the last song is the best.

A Greenfinch was calling on the other side of the Vista. There are not many of these in the park, nor Goldfinches, for some reason, although Chaffinches are abundant.

A typical midsummer Saturday, and the park was full of people, so there was little unusual to see in the way of bird life. There is a second blond Greylag Goose on the lake, darker than the one that arrived earlier this year.

And here is one of the young Grey Herons gazing pensively across the lake, almost certainly thinking of its next meal.

There was more interest under water. Nigel Reeve had seen my report of 12 May about the return of the crayfish after they had been wiped out in 2008 by an accident when workmen cleaning the Diana fountain released poisonous chemicals into the lake. And he had asked me to get a picture of one of the new crayfish, if possible.

The original ones in the lake were Turkish Crayfish (Astacus leptodactylus), and he thought that the new ones might be American Signal Crayfish (Pacifastacus leniusculus), which have become a pest species in Britain over the past few decades. Neither is native, of course, and they are none too welcome as they predate the larvae of native fish. It was noticeable that after the poisoning incident there was a brief boom in the number of fish in the lake.

The boss of the boat hire firm Bluebird Boats, Peter Scott, had told me that his workers had found lots of large crayfish in the lake. I happened to meet him on my way round the lake, and asked him if, the next time he found one, he could photograph it to determine its species. But he very kindly offered to find me one there and then, and sent me out with two of his men in a motor boat to bring one up.

Before 2008, there was a man who set crayfish traps in the lake, quite unofficially, and sold his catch to local restaurants. Now it seems that someone has resumed the trade. There were two crayfish traps in the shallow water between the boathouses, and after we had found them -- with some difficulty because the algae hid everything -- we retrieved two crayfish, one of which was very large, more like a junior lobster.

I thought this must be a Signal Crayfish because of its huge size and massive right claw. But when I got home and looked it up on the web, I changed my mind. Unlike a Signal Crayfish, it doesn't have any trace of red on its body, and it looks just like the Turkish crayfish shown here. So maybe a few survived in 2008, and have gradually bred up to large numbers again. Here is a close-up of the same creature.